El domingo, 10 de julio de 2022 a las 10:22:30 UTC-4, det...@outlook.com escribió:
> On Saturday, July 9, 2022 at 8:19:51 PM UTC-5, Paparios wrote:

> > You forgot to include the equation below that quote:
> > "It follows, further, that the velocity of light c cannot be altered by composition
> > with a velocity less than that of light. For this case we obtain:
> >
> > V=(c+w)/(1+w/c)=c"
> >
> > Before that Einstein wrote: "If w also has the direction of the axis of X, we get
> > V = (v + w)/(1 + vw/c^2).
> > It follows from this equation that from a composition of two velocities which
> > are less than c, there always results a velocity less than c".
> >
> > In other words, the composition of two speeds below c always result in a speed V<c.
> > If one of the speeds is light (ie v=c), then the resulting speed is not c+w (which is what you believe) but c.

> It doesn't matter how many equations you can twist to fit your BELIEFS,
> EXPERIMENTS still show that an observer approaching a light source will
> receive the light at c+v, where v is the speed of the observer and c is the
> speed of light.
>

If that c+v was to be true (which it is not) then an emitter moving at speed v would emit light not at speed c but at speed c+v, which obviously contradicts the second postulate. The second postulate (that you recognized) says:

"light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body"

Light moves through space at speed c. When you, wrongly, assert that light is received by a moving receiver as c+v, you are using the speed v which is a speed defined relative to the emitter and corresponds to the closing speed.

> Here a list of such experiments: http://www.ed-lake.com/Variable-Speed-of-Light-Experiments.html
>

Most of your explanations of those experiments are your own misunderstandings of SR.

On Sunday, July 10, 2022 at 7:36:22 AM UTC-7, det...@outlook.com wrote:
> > > That first part of Einstein's paper ... introduces two …POSTULATES…
> >
> > To be more accurate, in the introduction he announces his intention to elevate the (well known) principle of relativity to the status of a postulate, and in addition to postulate another (new) principle, that he later called the principle of the invariance of the speed of light. He fulfills these intentions at the beginning of Section 2, after establishing in Section 1 the crucial systems of coordinates in terms of which the two principles (that he will take as postulates) are precisely and unambiguously defined.
> >
> > > that APPEAR to be "irreconcilable,"
> >
> > Yes, they appear irreconcilable because, as he explains in detail, the combination of the two principles that he has taken as postulates imply that every pulse of light moves in vacuum at the definite speed c in terms of every system of coordinates of the special type he defined in Section 1. This would be impossible if those standard coordinate systems were related to each other as Galileo and Newton thought, such that speeds are simply additive. Einstein showed that those coordinate systems are related in a different way, that involves time dilation, length contraction, and the skew of simultaneity.
> >
> > > the rest of the paper explains how they ARE reconciled if time is variable
> > > and is slowed down by motion.
> >
> > Well, that’s one part of the reconcilation, but by itself time dilation cannot accomplish the reconciliation. Einstein carefully describes all three ingredients that are necessary to reconcile those two postulated principles, namely, time dilation, length contraction, and the skew of simultaneity.
> >
> > With this understanding, every competent person agrees with Einstein that light moves (in vacuum) at the definite speed c in terms of every standard system of inertial coordinates. This follows from Einstein’s two postulated principles, as he clearly states and explains. This is not a controversial point.
>
> It is obviously a "controversial point" if MANY experiments show that
> light will hit an oncoming object at c+v where v is the speed of the object
> and c is the speed of light.

No, every experiment (so far) is perfectly consistent with the principles of special relativity (that Einstein postulated), including the fact that the principles imply that light moves in vacuum at the speed c in terms of every standard system of inertial coordinates.

Remember, you mistakenly thought that radar speed guns measure the speed of light, but your misunderstanding was corrected by pointing out that they actually measure the difference between the frequencies of the direct and reflected signals. This isn't measuring the speed of light.

We also pointed out that the closing speed is c+v for an approaching target in the reference system of the gun, but that the speed is c in terms of the standard inertial coordinates (that Einstein described in Section 1) in which the target is at rest, and it is also c in terms of the standard inertial coordinates in which the gun is at rest, and in terms of every other standard system of inertial coordinates as well. This is the seemingly irreconcilable proposition that Einstein famously explained, and that you are denying, but every competent person understands why you are wrong, as clearly explained in Einstein’s paper. It is not controversial at all.

On 2022-07-10 14:36:20 +0000, Ed Lake said:

> It is obviously a "controversial point" if MANY experiments show that
> light will hit an oncoming object at c+v where v is the speed of the
> objectand c is the speed of light. Here's a list of some of those
> experiments:
> http://www.ed-lake.com/Variable-Speed-of-Light-Experiments.html

None of those descriptions of experiments demonstrate that the
result would be different in a ballistic theory from an ether theory
or any other theory. Therefore the page does not demonstrate
anything about the speed of light. Whether the experiments when
properly analyzed show one way or other is not told in the page.

Mikko

On 2022-07-10 14:36:20 +0000, Ed Lake said:

> A "postulate" is defined as "to suggest or assume the existence, fact,
> or truth of(something) as a basis for reasoning, discussion, or belief."

In this sense Einsteins principles as presented in section 2 of
"Zur Elektrodynamik bewegter Körper" are postulates. Whether they
are called "postulates" or "priciples" or "hypotheses" or something
else is a matter of taste more than a matter of opinion.

Mikko

On Sunday, July 10, 2022 at 8:35:04 AM UTC-5, Ufonaut wrote:
> On Sunday, July 10, 2022 at 2:05:20 AM UTC+10, wrote:
> > On Saturday, July 9, 2022 at 10:36:41 AM UTC-5, Paparios wrote:
> > > El sábado, 9 de julio de 2022 a las 10:41:19 UTC-4, escribió:
> > > > On Friday, July 8, 2022 at 4:56:44 PM UTC-5, RichD wrote:
> > > > > On July 8, RichD wrote:
> > > > > >>>> The Second Postulate is: "light is always propagated in empty
> > > > > >>>> space with a definite velocity c which is independent of the state of motion
> > > > > >>>> of the EMITTING body."
> > > > > >
> > > > > >>> It's quite obvious it means the receiver/observer (in this case the
> > > > > >>> front of the car) will receive the photon at c, regardless of the motion
> > > > > >>> or lack thereof of the photon's source (radar gun).
> > >
> > > > WRONG! It says the EMITTER always EMITS light at c. Einstein's Second
> > > > Postulate says absolutely NOTHING about what a RECEIVER/OBSERVER will see.
> > > Again you do not understand English. That introduction says:
> > > "light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body".
> > Agreed.
> > >
> > > The "state of motion of the emitting body" clearly means either the body is stationary or the body is moving. Therefore, a) if the emitter is stationary, light will propagate at speed c. b) If the emitter is moving, light will also propagate at speed c.
> > Agreed.
> > >
> > > Say the emitter is at point E and the receiver is at point R.
> > >
> > > Case 1) Both E and R are stationary E.....c-->.......................R E emits at speed c, R receives at speed c.
> > Agreed.
> > > Case 2) E is moving at speed v, R is stationary, E emits light at speed c, R receives the light at speed c.
> > Agreed.
> > > Case 3) E is stationary, R is moving towards E at speed w. E emits light at speed c, R receives the light at speed V=(c+w)/(1+w/c)=c
> > > (see equations in section 5 of the paper).
> > >
> > > Therefore in all cases, the receiver R receives the light at speed c.
> > Nonsense. Section 5 of Einstein's paper says, "It follows, further,
> > that the velocity of light c cannot be altered by composition
> > with a velocity less than that of light." In other words, when an
> > observer receives light at c+v, v is his speed and c is still the speed
> > of light.
> Except this contradicts your earlier statement :
> On Sunday, July 10, 2022 at 12:41:19 AM UTC+10, wrote:
> > A RECEIVER or observer will observe light as moving at c+v if
> > the receiver is moving toward the emitter at speed v, and at c-v if the receiver
> > is moving away from the emitter at speed v.

How do those statements disagree? They say the SAME THING.

> So for an emitter moving at speed w, and a receiver keeping an unchanging distance away - ie, w " is his speed" and also therefore the v of your quote here "moving toward the emitter at speed v" is = 0), then "A RECEIVER or observer will observe light as moving at c+v" = c+0 = c, so NOT at c+w.

If the emitter and receiver are moving together at the same speed,
their relative speed is zero. Light will be emitted at c and will be
received at c.

If the emitter and receiver are NOT moving together at the same speed,
the emitter will still emit light at c, but the receiver will receive that light
at c+v or c-v depending on his speed relative to the emitter.

>
> You clearly regard the speed of the receiver (relative to those "stationary points in space"?) to be of paramount importance - such that for example it determines how much that receiver is "time dilated", (and of course you regard velocity time dilation as absolute just as gravitational time dilation is) .
>
> However, you never give any indication of what constitutes those "stationary points", and therefore for any pair of observers which one is the one that gets time-dilated. For example, at times you appear to regard the surface of the earth as "stationary" - certainly that the photons from a radar gun on the surface of the earth travel at c relative to the surface of the earth, despite the fact that the surface of the earth is certainly moving relative to any "stationary points in space". So what's so special about the surface of earth compared to, say, a space station that is stationary relative to the sun - specifically, what is your basis for declaring that it is MORONIC to consider that space station as the one that is stationary and that it is the earth that is moving (in its orbit) ?

Light is emitted from stationary points in space, but the frequency of
that light will be affected by the speed at which the atom that emitted
the light is traveling. So, there's no way to measure speeds relative to
a "stationary point in space." All you can do is measure the speed of
one emitting atom versus another.

The International Space Station (ISS) is moving at 17,400 mph relative to the
surface of the earth. Relative to the surface of the sun, the ISS is ALSO moving
at 67,000 mph. Relative to the center of the Milky Way galaxy, the ISS is ALSO
moving at 560,000 mph.

You ask about "a space station that is stationary relative to the sun." There
is no such thing. If it was not moving, the ISS would be pulled into the sun by
the sun's gravity. If the ISS was not moving around the earth, it would fall
to earth, pulled down by the earth's gravity.

You ask: "what is your basis for declaring that it is MORONIC to consider that
space station as the one that is stationary and that it is the earth that is
moving (in its orbit)?"

The question makes no sense. The earth cannot orbit the ISS. The earth's
gravity would pull the ISS down to the surface of the earth.

I think you are trying to ask how you can tell which object in space is moving
the fastest when there is nothing else to measure their two speeds against.

You can do it if both have the equipment to transmit light at a specific
frequency and the equipment to measure the frequency of received light.

If object-A and object-B are moving toward each other, and if object-A emits
light toward object-B, if object-A is the faster moving object, object-B will
receive that light at a higher frequency. If object-A is the slower moving
object, object-B will receive the light at a lower frequency. Object-A can
say, "I measure your approach speed as 90 mph," and Object-B can say,
"I measure your approach speed as 12 mph." Object B is moving faster,
but BOTH will have to slow down to avoid a collision.

If they become stationary relative to one another, they will send and receive
the light at the same frequency.

Ed

On Sunday, July 10, 2022 at 7:43:55 AM UTC-7, det...@outlook.com wrote:
> Einstein ASSUMES the two postulates are true and then begins a point by point
> explanation of how TIME DILATION allows them to reconcile.

The first time you made that erroneous statement it could have been excused as just a mistake, but after you’ve been told many times that it is false (because Einstein explicitly explained that the reconciliation requires not just time dilation but also length contraction and the skew of simultaneity), you have no excuse for continuing to repeat the falsehood. You need all three ingredients, not just one.

> Why do YOU and others here refuse to discuss that point? It SAYS that
> time goes more slowly for a faster moving object.

Well, it says proper time runs more slowly, by the factor 1/sqrt(1-v^2/c^2), for a moving object in terms of the standard inertial coordinates in which it is moving at speed v, and this does indeed imply that time advances more slowly for a clock moving in a circle in terms of the inertial coordinates in which a clock at the center is at rest, everything else being equal.
Actually, everything else is not equal for clocks at the poles and equator of the earth, because of the oblate shape of the earth and the variations in the gravitational potential, but those don’t falsify the basic point Einstein was making about the secular difference in elapsed times for clocks following different paths.

On Sunday, July 10, 2022 at 10:36:19 AM UTC-5, Paparios wrote:
> El domingo, 10 de julio de 2022 a las 10:22:30 UTC-4, escribió:
> > On Saturday, July 9, 2022 at 8:19:51 PM UTC-5, Paparios wrote:
>
> > > You forgot to include the equation below that quote:
> > > "It follows, further, that the velocity of light c cannot be altered by composition
> > > with a velocity less than that of light. For this case we obtain:
> > >
> > > V=(c+w)/(1+w/c)=c"
> > >
> > > Before that Einstein wrote: "If w also has the direction of the axis of X, we get
> > > V = (v + w)/(1 + vw/c^2).
> > > It follows from this equation that from a composition of two velocities which
> > > are less than c, there always results a velocity less than c".
> > >
> > > In other words, the composition of two speeds below c always result in a speed V<c.
> > > If one of the speeds is light (ie v=c), then the resulting speed is not c+w (which is what you believe) but c.
>
> > It doesn't matter how many equations you can twist to fit your BELIEFS,
> > EXPERIMENTS still show that an observer approaching a light source will
> > receive the light at c+v, where v is the speed of the observer and c is the
> > speed of light.
> >
> If that c+v was to be true (which it is not) then an emitter moving at speed v would emit light not at speed c but at speed c+v, which obviously contradicts the second postulate. The second postulate (that you recognized) says:
>
> "light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body"
> Light moves through space at speed c. When you, wrongly, assert that light is received by a moving receiver as c+v, you are using the speed v which is a speed defined relative to the emitter and corresponds to the closing speed.

Light is ALWAYS EMITTED at c.
So, light ALWAYS TRAVELS at c.
However, light can be RECEIVED at c+v or c-v if the RECEIVER is moving at v toward or away from the emitter.
If you want to call it "the closing speed," that doesn't change anything.
When radar guns measure the speed of an oncoming vehicle, they measure the "closing speed."

How can you not understand that?????

> > Here a list of such experiments: http://www.ed-lake.com/Variable-Speed-of-Light-Experiments.html
> >
> Most of your explanations of those experiments are your own misunderstandings of SR.

That is your OPINION. I have no interest in arguing OPINIONS.

Ed

On Sunday, July 10, 2022 at 11:04:48 AM UTC-5, Stan Fultoni wrote:
> On Sunday, July 10, 2022 at 7:43:55 AM UTC-7, wrote:
> > Einstein ASSUMES the two postulates are true and then begins a point by point
> > explanation of how TIME DILATION allows them to reconcile.
> The first time you made that erroneous statement it could have been excused as just a mistake, but after you’ve been told many times that it is false (because Einstein explicitly explained that the reconciliation requires not just time dilation but also length contraction and the skew of simultaneity), you have no excuse for continuing to repeat the falsehood. You need all three ingredients, not just one.

Has any experiment ever verified "length contraction"?
The "skew of simultaneity" is certainly part of Relativity, but "the skew of
simultaneity" is mostly about what might be called "optical illusions."
Time Dilation is the only NEW DISCOVERY explained in Einstein's paper.

>
> > Why do YOU and others here refuse to discuss that point? It SAYS that
> > time goes more slowly for a faster moving object.
> Well, it says proper time runs more slowly, by the factor 1/sqrt(1-v^2/c^2), for a moving object in terms of the standard inertial coordinates in which it is moving at speed v, and this does indeed imply that time advances more slowly for a clock moving in a circle in terms of the inertial coordinates in which a clock at the center is at rest, everything else being equal..
> Actually, everything else is not equal for clocks at the poles and equator of the earth, because of the oblate shape of the earth and the variations in the gravitational potential, but those don’t falsify the basic point Einstein was making about the secular difference in elapsed times for clocks following different paths.

So why even mention it? You just make the FACT of time dilation less
clear by bringing up irrelevancies.

Ed

On 7/10/2022 10:43 AM, Ed Lake wrote:
> On Sunday, July 10, 2022 at 12:33:27 AM UTC-5, Volney wrote:
>> On 7/9/2022 3:15 PM, Ed Lake wrote:
>>> On Saturday, July 9, 2022 at 12:41:57 PM UTC-5, Volney wrote:
>>>> On 7/9/2022 1:06 PM, Ed Lake wrote:
>>>>> On Saturday, July 9, 2022 at 11:51:37 AM UTC-5, Volney wrote:
>>>>>> On 7/9/2022 10:41 AM, Ed Lake wrote:
>>>>>>> On Friday, July 8, 2022 at 4:56:44 PM UTC-5, RichD wrote:
>>>>>>>> On July 8, RichD wrote:
>>>>>>>>>>>> The Second Postulate is: "light is always propagated in empty
>>>>>>>>>>>> space with a definite velocity c which is independent of the state of motion
>>>>>>>>>>>> of the EMITTING body."
>>>>>>>>>
>>>>>>>>>>> It's quite obvious it means the receiver/observer (in this case the
>>>>>>>>>>> front of the car) will receive the photon at c, regardless of the motion
>>>>>>>>>>> or lack thereof of the photon's source (radar gun).
>>>>>>>
>>>>>>> WRONG! It says the EMITTER always EMITS light at c. Einstein's Second
>>>>>>> Postulate says absolutely NOTHING about what a RECEIVER/OBSERVER will see.
>>>>>> It most certainly does! The second postulate: "2. Any ray of light moves
>>>>>> in the “stationary” system of co-ordinates with the determined velocity
>>>>>> c, whether the ray be emitted by a stationary or by a moving body."
>>>>>
>>>>> That is NOT Einstein's Second Postulate! It is a "principle" Einstein uses later
>>>>> in his paper where he is talking about a "'stationary' system of coordinates."
>>>> Einstein NEVER used the word "postulate" in his paper! He wrote in
>>>> German, and he didn't use the German word "Postulat", either.
>>>> "Postulate" is the creation of a translator! He used German words which
>>>> could be translated as premise, principle, assumption, claim or
>>>> postulate.
>>>
>>> The translator used the BEST word.
>> So you DO believe the translator's input outranks Einstein's!
>>>> So you CANNOT claim the use of the word "postulate" in the
>>>> abstract [.......]
>>>
>>> That first part of Einstein's paper is obviously NOT AN ABSTRACT.
>>> It's an INTRODUCTION.
>> It's an abstract, just like every similar paper has. Its purpose is to
>> assist a researcher to decide whether to look at the paper further or
>> not, depending on what is being researched.
>>
>>> It introduces two IDEAS/POSTULATES/ASSUMPTIONS
>>
>> Rather it states that two postulates/assumptions WILL be introduced in
>> the meat of the paper, which he does.
>>> that APPEAR to be "irreconcilable,"
>> They appear to be irreconcilable because, for Frame 1 and Frame 2 moving
>> relatively to each other at a speed v, and the Frame 1 observer measures
>> light as c, the first postulate suggests Frame 2 *should* measure light
>> at c+v (or c-v) in order for the first postulate to hold and Newton's
>> equations hold good. Einstein already knew this sure looks very wrong,
>> he's saying he knows that and he will explain it.
>>> and the rest of the paper explains how
>>> they ARE reconciled if time is variable and is slowed down by motion.
>> No he explains it by time dilation, length contraction and the skew of
>> simultaneity. (Read the paper!)
>>> Einstein
>>> summed up his theory this way at the end of Part 4:
>> That's not a summary but a further explanation. In addition, that is the
>> one part of the paper you could argue is wrong (E didn't know of GR yet,
>> nor that the earth isn't spherical, nor that it is really a "traveling
>> twin" problem. Pure time dilation as described only works in a straight
>> line inertial motion)
>>>
>>> "Thence we conclude that a balance-clock at the equator must go more
>>> slowly, by a very small amount, than a precisely similar clock situated at
>>> one of the poles under otherwise identical conditions."
>>>
>>> An "abstract" is a SUMMARY of a paper.
>> Which is exactly what the first part is.
>
> If the first part of the paper is a "summary" (which it is NOT), how can it
> totally IGNORE the key POINT of the paper:
>
> "Thence we conclude that a balance-clock at the equator must go more slowly,
> by a very small amount, than a precisely similar clock situated at one of the
> poles under otherwise identical conditions."

As I already mentioned, that statement is technically wrong as it
ignores gravitational time dilation (unknown at the time, later
discovered by Einstein) and the fact the earth is oblate, not spherical.
>
> And why do YOU and others here refuse to discuss that point? It SAYS that
> time goes more slowly for a faster moving object.

Additionally, the pure time dilation is for an INERTIAL frame, no
acceleration. A person at the equator is moving in a circle,
technically constantly accelerating. This problem becomes one not of a
demonstration of time dilation but a traveling twin situation where the
person on the equator moves in a complete circle to the starting point
(in the frame where the center of the earth is stationary).

The classic traveling twin is out-and-back, and a circle is much more
complicated than that to analyze. However it can be approximated as 24 1
hour trips in a 24-gon pattern, or 86,400 1 second trips. You can work
out the spacetime diagram if you wish, but the end the equator "twin"
passes through more spacetime on the complex journey than the North Pole
twin, so he experiences less proper time when ignoring GR and oblateness
(as Einstein unknowingly does).

It does NOT mean anything as silly as a different length of a second,
that implies an absolutely stationary frame, disallowed by the first
postulate.

On Sunday, 10 July 2022 at 18:56:14 UTC+2, Volney wrote:

> Additionally, the pure time dilation is for an INERTIAL frame, no
> acceleration. A person at the equator is moving in a circle,
> technically constantly accelerating. This problem becomes one not of a
> demonstration of time dilation but a traveling twin situation where the
> person on the equator moves in a complete circle to the starting point
> (in the frame where the center of the earth is stationary).

In the meantime in the real world, of course, forbidden
by your bunch of idiots GPS and TAI keep measuring
t'==t, just like all serious clocks always did.

On Sunday, July 10, 2022 at 9:50:47 AM UTC-7, det...@outlook.com wrote:
> > > Einstein ASSUMES the two postulates are true and then begins a point by point
> > > explanation of how TIME DILATION allows them to reconcile.
> > The first time you made that erroneous statement it could have been excused as just a mistake, but after you’ve been told many times that it is false (because Einstein explicitly explained that the reconciliation requires not just time dilation but also length contraction and the skew of simultaneity), you have no excuse for continuing to repeat the falsehood. You need all three ingredients, not just one.
>
> Has any experiment ever verified "length contraction"?

Yes, in fact every aspect of special relativity has been thoroughly tested and confirmed experimentally. For example, the arms of a Michelson interferometer undergo measurable length contraction. In addition, special relativity would be logically self-contradictory without all three ingredients.

> The "skew of simultaneity" is certainly part of Relativity, but "the skew of
> simultaneity" is mostly about what might be called "optical illusions."

No it's not. This is actually the aspect of special relativity for which Einstein was most famous, i.e., the realization that two events that are simultaneous in terms of one standard system of inertial coordinates are not simultaneous in terms of another. This is not any kind of illusion, it is a verifiable (and verified) objective fact.

> Time Dilation is the only NEW DISCOVERY explained in Einstein's paper.

That's very far from the truth. Actually Lorentz already had time dilation in 1892. Again, the startling insight that Einstein was most credited with was the relativity of simultaneity… although even this was *implicit* in Lorentz’s earlier work. Lorentz admitted that he had not fully appreciated it until Einstein pointed out the reciprocal skew of simultaneity explicitly, reconciling it with the principle of relativity.

> > > Why do YOU and others here refuse to discuss that point? It SAYS that
> > > time goes more slowly for a faster moving object.
> > Well, it says proper time runs more slowly, by the factor 1/sqrt(1-v^2/c^2), for a moving object in terms of the standard inertial coordinates in which it is moving at speed v, and this does indeed imply that time advances more slowly for a clock moving in a circle in terms of the inertial coordinates in which a clock at the center is at rest, everything else being equal.
> > Actually, everything else is not equal for clocks at the poles and equator of the earth, because of the oblate shape of the earth and the variations in the gravitational potential, but those don’t falsify the basic point Einstein was making about the secular difference in elapsed times for clocks following different paths.
>
> So why even mention it? You just make the FACT of time dilation less
> clear by bringing up irrelevancies.

It doesn’t make time dilation any less clear to point out the fact that the relations between the proper times of sea-level clocks at the poles and equator actually involve other factors (gravitational potential) that make it a more complicated example. Again, no competent person disputes the facts of relativistic time dilation… but it is also true that no competent person disputes the facts of length contraction and the skew of simultaneity either… and yet you dispute the latter two.

On Sunday, July 10, 2022 at 9:28:07 AM UTC-7, det...@outlook.com wrote:
> Light is ALWAYS EMITTED at c.
> So, light ALWAYS TRAVELS at c.

Those statements are strictly meaningless because you haven’t specified the system of coordinates. It is quite easy to define coordinate systems in which the speed of light is not c. The speed of light is c just in terms of the standard systems of inertial coordinates, defined as explained in Section 1 of Einstein’s paper. (By the way, many of your other comments suggest that youthink the words ‘propagated’ and ‘emitted’ are synonyms… they are not.)

> However, light can be RECEIVED at c+v or c-v if the RECEIVER is moving at v toward or away from the emitter. If you want to call it "the closing speed," that doesn't change anything.

(The misconception of every newsgroup poster is always contained in the words he types in caps.) Prior to the discovery of special relativity, it was believed that there is no difference between relative speed and closing speed, but special relativity revealed that there is a difference, and when you talk about light being *received* at a certain speed by an object, unless you specify otherwise you are interpreted to be referring to the relative speed, not the closing speed. The relative speed is the speed in terms of the standard inertial coordinates in which the object is at rest.

> When radar guns measure the speed of an oncoming vehicle, they measure the "closing speed."

No, they measure the relative speed, not the closing speed. Now, for the range of speeds of automobiles, etc., the difference is imperceptibly small, so you obviously can’t use radar speed guns to demonstrate this difference with ordinary every-day objects. The only thing a radar gun demonstrates for low speeds is the first order Doppler effect. However, if you had an object directly approaching you at v = 0.8c in terms of your standard inertial coordinate system, and you point a radar gun at the object, according to your claim the radar gun would read the closing speed of c+v = 1.8c, but that is incorrect. The gun would actually read 0.8c. This is the relative speed, not the closing speed.

On Sunday, July 10, 2022 at 9:28:07 AM UTC-7, det...@outlook.com wrote:
> Light is ALWAYS EMITTED at c.
> So, light ALWAYS TRAVELS at c.

Those statements are strictly meaningless because you haven’t specified the system of coordinates. It's quite easy to define coordinate systems in which the speed of light is not c. The speed of light is c just in terms of the standard systems of inertial coordinates, defined as explained in Section 1 of Einstein’s paper. (By the way, many of your other comments suggest that youthink the words ‘propagated’ and ‘emitted’ are synonyms… they are not.)

> However, light can be RECEIVED at c+v or c-v if the RECEIVER is moving at v toward or away from the emitter. If you want to call it "the closing speed," that doesn't change anything.

Prior to the discovery of special relativity, it was believed that there is no difference between relative speed and closing speed, but special relativity revealed that there is a difference, and when you talk about light being *received* at a certain speed by an object, unless you specify otherwise you are interpreted to be referring to the relative speed, not the closing speed. The relative speed is the speed in terms of the standard inertial coordinates in which the object is at rest.

> When radar guns measure the speed of an oncoming vehicle, they measure the "closing speed."

No, they measure the relative speed, not the closing speed. For the range of speeds of automobiles, etc., the difference is imperceptibly small, so you obviously can’t use radar speed guns to demonstrate this difference with ordinary every-day objects. The only thing a radar gun demonstrates for low speeds is the first order Doppler effect. For example, if you are driving on the road at 50 mph (relative to the road) and someone is driving directly toward you at 50 mph (relative to the road), the closing speed would be 100 mph, but that isn’t exactly what the radar gun would read. The radar gun will read the relative speed between you and the approaching car, which according to special relativity is (50 + 50)/[1 + (50)(50)/c^2], which is 99.9999999999994 mph. This shows the futility of trying to use radar speed guns in ordinary situations to demonstrate relativistic effects.

To actually show the relativistic effects, you would need a situation such as two spaceships directly approaching each other, one moving to the left at 0.6c and the other moving to the right at 0.6c (both in terms of the Sun’s inertial coordinate system). The closing speed is 1.2c, but the relative speed between the rockets is 0.88235c, and this is what a radar gun pointed from one at the other would read.

On Sunday, 10 July 2022 at 19:32:20 UTC+2, Stan Fultoni wrote:
> On Sunday, July 10, 2022 at 9:50:47 AM UTC-7, det...@outlook.com wrote:
> > > > Einstein ASSUMES the two postulates are true and then begins a point by point
> > > > explanation of how TIME DILATION allows them to reconcile.
> > > The first time you made that erroneous statement it could have been excused as just a mistake, but after you’ve been told many times that it is false (because Einstein explicitly explained that the reconciliation requires not just time dilation but also length contraction and the skew of simultaneity), you have no excuse for continuing to repeat the falsehood.. You need all three ingredients, not just one.
> >
> > Has any experiment ever verified "length contraction"?
> Yes, in fact every aspect of special relativity has been thoroughly tested and confirmed experimentally. For example, the arms of a Michelson interferometer undergo measurable length contraction. In addition, special relativity would be logically self-contradictory without all three ingredients.
> > The "skew of simultaneity" is certainly part of Relativity, but "the skew of
> > simultaneity" is mostly about what might be called "optical illusions."
> No it's not. This is actually the aspect of special relativity for which Einstein was most famous, i.e., the realization that two events that are simultaneous in terms of one standard system of inertial coordinates are not simultaneous in terms of another. This is not any kind of illusion, it is a verifiable (and verified) objective fact.

Realization that? Rather, creation of wannabe standard where
things go crazy.

On Monday, July 11, 2022 at 1:58:08 AM UTC+10, det...@outlook.com wrote:
> On Sunday, July 10, 2022 at 8:35:04 AM UTC-5, Ufonaut wrote:
> > On Sunday, July 10, 2022 at 2:05:20 AM UTC+10, wrote:
> > > On Saturday, July 9, 2022 at 10:36:41 AM UTC-5, Paparios wrote:
> > > > El sábado, 9 de julio de 2022 a las 10:41:19 UTC-4, escribió:
> > > > > On Friday, July 8, 2022 at 4:56:44 PM UTC-5, RichD wrote:
> > > > > > On July 8, RichD wrote:
> > > > > > >>>> The Second Postulate is: "light is always propagated in empty
> > > > > > >>>> space with a definite velocity c which is independent of the state of motion
> > > > > > >>>> of the EMITTING body."
> > > > > > >
> > > > > > >>> It's quite obvious it means the receiver/observer (in this case the
> > > > > > >>> front of the car) will receive the photon at c, regardless of the motion
> > > > > > >>> or lack thereof of the photon's source (radar gun).
> > > >
> > > > > WRONG! It says the EMITTER always EMITS light at c. Einstein's Second
> > > > > Postulate says absolutely NOTHING about what a RECEIVER/OBSERVER will see.
> > > > Again you do not understand English. That introduction says:
> > > > "light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body".
> > > Agreed.
> > > >
> > > > The "state of motion of the emitting body" clearly means either the body is stationary or the body is moving. Therefore, a) if the emitter is stationary, light will propagate at speed c. b) If the emitter is moving, light will also propagate at speed c.
> > > Agreed.
> > > >
> > > > Say the emitter is at point E and the receiver is at point R.
> > > >
> > > > Case 1) Both E and R are stationary E.....c-->........................R E emits at speed c, R receives at speed c.
> > > Agreed.
> > > > Case 2) E is moving at speed v, R is stationary, E emits light at speed c, R receives the light at speed c.
> > > Agreed.
> > > > Case 3) E is stationary, R is moving towards E at speed w. E emits light at speed c, R receives the light at speed V=(c+w)/(1+w/c)=c
> > > > (see equations in section 5 of the paper).
> > > >
> > > > Therefore in all cases, the receiver R receives the light at speed c.
> > > Nonsense. Section 5 of Einstein's paper says, "It follows, further,
> > > that the velocity of light c cannot be altered by composition
> > > with a velocity less than that of light." In other words, when an
> > > observer receives light at c+v, v is his speed and c is still the speed
> > > of light.
> > Except this contradicts your earlier statement :
> > On Sunday, July 10, 2022 at 12:41:19 AM UTC+10, wrote:
> > > A RECEIVER or observer will observe light as moving at c+v if
> > > the receiver is moving toward the emitter at speed v, and at c-v if the receiver
> > > is moving away from the emitter at speed v.
> How do those statements disagree? They say the SAME THING.
> > So for an emitter moving at speed w, and a receiver keeping an unchanging distance away - ie, w " is his speed" and also therefore the v of your quote here "moving toward the emitter at speed v" is = 0), then "A RECEIVER or observer will observe light as moving at c+v" = c+0 = c, so NOT at c+w.
> If the emitter and receiver are moving together at the same speed,
> their relative speed is zero. Light will be emitted at c and will be
> received at c.
>
> If the emitter and receiver are NOT moving together at the same speed,
> the emitter will still emit light at c, but the receiver will receive that light
> at c+v or c-v depending on his speed relative to the emitter.

OK, Let’s look at Case 2 above : “Case 2) E is moving at speed v, R is stationary,” - so “the emitter and receiver are NOT moving together at the same speed”, there is a relative velocity v between them.

Which means you are saying BOTH that “R receives the light at speed c. > > > Agreed. “ (so NOT at c+v or c-v)
AND ALSO “the receiver will receive that light at c+v or c-v depending on his speed relative to the emitter.”

> >
> > You clearly regard the speed of the receiver (relative to those "stationary points in space"?) to be of paramount importance - such that for example it determines how much that receiver is "time dilated", (and of course you regard velocity time dilation as absolute just as gravitational time dilation is) .
> >
> > However, you never give any indication of what constitutes those "stationary points", and therefore for any pair of observers which one is the one that gets time-dilated. For example, at times you appear to regard the surface of the earth as "stationary" - certainly that the photons from a radar gun on the surface of the earth travel at c relative to the surface of the earth, despite the fact that the surface of the earth is certainly moving relative to any "stationary points in space". So what's so special about the surface of earth compared to, say, a space station that is stationary relative to the sun - specifically, what is your basis for declaring that it is MORONIC to consider that space station as the one that is stationary and that it is the earth that is moving (in its orbit) ?
> Light is emitted from stationary points in space, but the frequency of
> that light will be affected by the speed at which the atom that emitted
> the light is traveling. So, there's no way to measure speeds relative to
> a "stationary point in space."

Since “there's no way to measure speeds relative to a "stationary point in space.””, that means "stationary point in space.” has no effect (since any manifest effect CAN be measured) - which in turn means that by definition it may just as well not exist.

So do you have ANY basis for the claim that such absolute points exist ?

> All you can do is measure the speed of
> one emitting atom versus another.

> The International Space Station (ISS) is moving at 17,400 mph relative to the
> surface of the earth. Relative to the surface of the sun, the ISS is ALSO moving
> at 67,000 mph. Relative to the center of the Milky Way galaxy, the ISS is ALSO
> moving at 560,000 mph.

My point exactly. As you have been told many times, there is only relative motion. All motion is RELATIVE, not absolute - and therefore cannot give rise to absolute effects (such as an absolute one-way time dilation).

>
> You ask about "a space station that is stationary relative to the sun." There
> is no such thing. If it was not moving, the ISS would be pulled into the sun by
> the sun's gravity.

“a space station stationary relative to the sun” is clearly not referring to the ISS, but is a hypothetical.

OK, such a space station would eventually fall into the sun - but we can still perfectly validly consider the effects of Special Relativity over a SHORT period of time (so the amount of pulling is negligible). During such a time, which would you say is moving - that (hypothetical) space station, or the earth in its orbit ?
> You ask: "what is your basis for declaring that it is MORONIC to consider that
> space station as the one that is stationary and that it is the earth that is
> moving (in its orbit)?"
> The question makes no sense. The earth cannot orbit the ISS.

Again, forget the ISS.

You say it is moronic for an astronaut (eg on a rocket or “space station”) to regard himself as stationary and the earth as moving.
In other words you ALWAYS regard the earth as being the “stationary” one, and that therefore time dilation ONLY affects the astronaut, not the earth.

The point that I am trying to get you to acknowledge is that the earth has its own motion as well - such as its orbit around the sun.

>
> I think you are trying to ask how you can tell which object in space is moving
> the fastest when there is nothing else to measure their two speeds against.

Pretty much - or even : what do you even mean about “fastest” given “All you can do is measure the speed of one emitting atom versus another. “
So two atoms have relative speed between them of v; that is ALL the information you have, so SOLELY from that statement, it is meaningless to assert which is moving fastest !

>
> You can do it if both have the equipment to transmit light at a specific
> frequency and the equipment to measure the frequency of received light.
>
> If object-A and object-B are moving toward each other, and if object-A emits
> light toward object-B, if object-A is the faster moving object, object-B will
> receive that light at a higher frequency. If object-A is the slower moving
> object, object-B will receive the light at a lower frequency. Object-A can
> say, "I measure your approach speed as 90 mph," and Object-B can say,
> "I measure your approach speed as 12 mph." Object B is moving faster,
> but BOTH will have to slow down to avoid a collision.

El domingo, 10 de julio de 2022 a las 12:28:07 UTC-4, det...@outlook.com escribió:
> On Sunday, July 10, 2022 at 10:36:19 AM UTC-5, Paparios wrote:

> > > It doesn't matter how many equations you can twist to fit your BELIEFS,
> > > EXPERIMENTS still show that an observer approaching a light source will
> > > receive the light at c+v, where v is the speed of the observer and c is the
> > > speed of light.
> > >
> > If that c+v was to be true (which it is not) then an emitter moving at speed v would emit light not at speed c but at speed c+v, which obviously contradicts the second postulate. The second postulate (that you recognized) says:
> >
> > "light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body"
> > Light moves through space at speed c. When you, wrongly, assert that light is received by a moving receiver as c+v, you are using the speed v which is a speed defined relative to the emitter and corresponds to the closing speed.
> Light is ALWAYS EMITTED at c.
> So, light ALWAYS TRAVELS at c.
> However, light can be RECEIVED at c+v or c-v if the RECEIVER is moving at v toward or away from the emitter.
> If you want to call it "the closing speed," that doesn't change anything.

Well, you should review your knowledge about it. Einstein himself explained this in chapter 9 of his 1920 book (see https://www.bartleby.com/173/9.html).
There we have a train and an embankment, with observers M' and M. The train is moving, relative to the embankment, at speed v. Just when both M and M' coincide at the train station, two lightning strikes simultaneously occur at points A and B (which are equidistant from observer M). Of course the light from those lightning strikes travels in all directions at speed c. Observer M receives the lights at the same time. Observer M', moving to the right at speed v, receives first the light coming from point B (since M' is now closer than M to point B) and later the light from point A (since M' is now farther than M from point A) As a consequence M' can say the lightning strikes were not simultaneous.

Note that the closing speed of the light coming from A arriving at M' is c-v (which does not mean the light is received at that speed). Also the closing speed of the light coming from point B arriving at M' is c+v (which again does not mean the light is received at that speed). Observer M', as the second postulate requires receives the light, which is moving at speed c, but at different locations relative to the emission of the lights.

On Monday, July 11, 2022 at 7:17:38 AM UTC-5, Ufonaut wrote:
> On Monday, July 11, 2022 at 1:58:08 AM UTC+10, wrote:
> > On Sunday, July 10, 2022 at 8:35:04 AM UTC-5, Ufonaut wrote:
> > > On Sunday, July 10, 2022 at 2:05:20 AM UTC+10, wrote:
> > > > On Saturday, July 9, 2022 at 10:36:41 AM UTC-5, Paparios wrote:
> > > > > El sábado, 9 de julio de 2022 a las 10:41:19 UTC-4, escribió:
> > > > > > On Friday, July 8, 2022 at 4:56:44 PM UTC-5, RichD wrote:
> > > > > > > On July 8, RichD wrote:
> > > > > > > >>>> The Second Postulate is: "light is always propagated in empty
> > > > > > > >>>> space with a definite velocity c which is independent of the state of motion
> > > > > > > >>>> of the EMITTING body."
> > > > > > > >
> > > > > > > >>> It's quite obvious it means the receiver/observer (in this case the
> > > > > > > >>> front of the car) will receive the photon at c, regardless of the motion
> > > > > > > >>> or lack thereof of the photon's source (radar gun).
> > > > >
> > > > > > WRONG! It says the EMITTER always EMITS light at c. Einstein's Second
> > > > > > Postulate says absolutely NOTHING about what a RECEIVER/OBSERVER will see.
> > > > > Again you do not understand English. That introduction says:
> > > > > "light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body".
> > > > Agreed.
> > > > >
> > > > > The "state of motion of the emitting body" clearly means either the body is stationary or the body is moving. Therefore, a) if the emitter is stationary, light will propagate at speed c. b) If the emitter is moving, light will also propagate at speed c.
> > > > Agreed.
> > > > >
> > > > > Say the emitter is at point E and the receiver is at point R.
> > > > >
> > > > > Case 1) Both E and R are stationary E.....c-->........................R E emits at speed c, R receives at speed c.
> > > > Agreed.
> > > > > Case 2) E is moving at speed v, R is stationary, E emits light at speed c, R receives the light at speed c.
> > > > Agreed.
> > > > > Case 3) E is stationary, R is moving towards E at speed w. E emits light at speed c, R receives the light at speed V=(c+w)/(1+w/c)=c
> > > > > (see equations in section 5 of the paper).
> > > > >
> > > > > Therefore in all cases, the receiver R receives the light at speed c.
> > > > Nonsense. Section 5 of Einstein's paper says, "It follows, further,
> > > > that the velocity of light c cannot be altered by composition
> > > > with a velocity less than that of light." In other words, when an
> > > > observer receives light at c+v, v is his speed and c is still the speed
> > > > of light.
> > > Except this contradicts your earlier statement :
> > > On Sunday, July 10, 2022 at 12:41:19 AM UTC+10, wrote:
> > > > A RECEIVER or observer will observe light as moving at c+v if
> > > > the receiver is moving toward the emitter at speed v, and at c-v if the receiver
> > > > is moving away from the emitter at speed v.
> > How do those statements disagree? They say the SAME THING.
> > > So for an emitter moving at speed w, and a receiver keeping an unchanging distance away - ie, w " is his speed" and also therefore the v of your quote here "moving toward the emitter at speed v" is = 0), then "A RECEIVER or observer will observe light as moving at c+v" = c+0 = c, so NOT at c+w.
> > If the emitter and receiver are moving together at the same speed,
> > their relative speed is zero. Light will be emitted at c and will be
> > received at c.
> >
> > If the emitter and receiver are NOT moving together at the same speed,
> > the emitter will still emit light at c, but the receiver will receive that light
> > at c+v or c-v depending on his speed relative to the emitter.
> OK, Let’s look at Case 2 above : “Case 2) E is moving at speed v, R is stationary,” - so “the emitter and receiver are NOT moving together at the same speed”, there is a relative velocity v between them.

Correct.

>
> Which means you are saying BOTH that “R receives the light at speed c. > > > Agreed. “ (so NOT at c+v or c-v)
> AND ALSO “the receiver will receive that light at c+v or c-v depending on his speed relative to the emitter.”

No. The receiver is stationary. Only the emitter is moving.
Einstein's Second Postulate says, "light is always propagated in empty
space with a definite velocity c which is independent of the state of
motion of the EMITTING body."

So, the emitter emits light at c even though the emitter is moving.
The receiver is stationary and receives the light at c.

The emitter is moving relative to the receiver. The receiver is STATIONARY,
which means the receiver is NOT moving. The FACT that the receiver
receives the light at c confirms that the receiver is not moving.
It also says that you cannot simply decide that the receiver is moving and
the emitter is stationary, because the FACT that the receiver receives the
light at c PROVES that the receiver is stationary.

> > >
> > > You clearly regard the speed of the receiver (relative to those "stationary points in space"?) to be of paramount importance - such that for example it determines how much that receiver is "time dilated", (and of course you regard velocity time dilation as absolute just as gravitational time dilation is) .
> > >
> > > However, you never give any indication of what constitutes those "stationary points", and therefore for any pair of observers which one is the one that gets time-dilated. For example, at times you appear to regard the surface of the earth as "stationary" - certainly that the photons from a radar gun on the surface of the earth travel at c relative to the surface of the earth, despite the fact that the surface of the earth is certainly moving relative to any "stationary points in space". So what's so special about the surface of earth compared to, say, a space station that is stationary relative to the sun - specifically, what is your basis for declaring that it is MORONIC to consider that space station as the one that is stationary and that it is the earth that is moving (in its orbit) ?
> > Light is emitted from stationary points in space, but the frequency of
> > that light will be affected by the speed at which the atom that emitted
> > the light is traveling. So, there's no way to measure speeds relative to
> > a "stationary point in space."
> Since “there's no way to measure speeds relative to a "stationary point in space.””, that means "stationary point in space.” has no effect (since any manifest effect CAN be measured) - which in turn means that by definition it may just as well not exist.

No, it just means we have no way of measuring the one way speed of light.
We only know HOW to measure the TWO WAY speed of light. The problem is
synchronizing clocks at both locations.

> So do you have ANY basis for the claim that such absolute points exist ?

Yes. When we receive light, it comes in a straight line from the stationary
point where it was emitted. When we look at Proxima Centauri, we see it
where it WAS two years ago. It is now millions of miles away from that point.
If you trace a photon back to where it originated, it originated at a stationary
point in space where the emitter happened to be when it emitted the photon.

> > All you can do is measure the speed of
> > one emitting atom versus another.
>
> > The International Space Station (ISS) is moving at 17,400 mph relative to the
> > surface of the earth. Relative to the surface of the sun, the ISS is ALSO moving
> > at 67,000 mph. Relative to the center of the Milky Way galaxy, the ISS is ALSO
> > moving at 560,000 mph.
> My point exactly. As you have been told many times, there is only relative motion. All motion is RELATIVE, not absolute - and therefore cannot give rise to absolute effects (such as an absolute one-way time dilation).

All motion is relative to the speed of light. Because the speed of light is the fastest
speed possible in our universe, all other speeds are a PERCENTAGE of the speed
of light.

17,400 mph is 0.0025946269802424% of the speed of light.
67,000 mph is 0.0099908050388646% of the speed of light.
560,000 mph is 0.083505236145734% of the speed of light.

Motion is SEEN as relative when I move away from you or when you move away
from me, but only ONE of us is moving at a greater percentage of the speed of light.

Click here to read the complete article

On Monday, July 11, 2022 at 9:46:18 AM UTC-5, Paparios wrote:
> El domingo, 10 de julio de 2022 a las 12:28:07 UTC-4, escribió:
> > On Sunday, July 10, 2022 at 10:36:19 AM UTC-5, Paparios wrote:
>
> > > > It doesn't matter how many equations you can twist to fit your BELIEFS,
> > > > EXPERIMENTS still show that an observer approaching a light source will
> > > > receive the light at c+v, where v is the speed of the observer and c is the
> > > > speed of light.
> > > >
> > > If that c+v was to be true (which it is not) then an emitter moving at speed v would emit light not at speed c but at speed c+v, which obviously contradicts the second postulate. The second postulate (that you recognized) says:
> > >
> > > "light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body"
> > > Light moves through space at speed c. When you, wrongly, assert that light is received by a moving receiver as c+v, you are using the speed v which is a speed defined relative to the emitter and corresponds to the closing speed.
> > Light is ALWAYS EMITTED at c.
> > So, light ALWAYS TRAVELS at c.
> > However, light can be RECEIVED at c+v or c-v if the RECEIVER is moving at v toward or away from the emitter.
> > If you want to call it "the closing speed," that doesn't change anything.
> Well, you should review your knowledge about it. Einstein himself explained this in chapter 9 of his 1920 book (see https://www.bartleby.com/173/9.html).
> There we have a train and an embankment, with observers M' and M. The train is moving, relative to the embankment, at speed v. Just when both M and M' coincide at the train station, two lightning strikes simultaneously occur at points A and B (which are equidistant from observer M). Of course the light from those lightning strikes travels in all directions at speed c. Observer M receives the lights at the same time. Observer M', moving to the right at speed v, receives first the light coming from point B (since M' is now closer than M to point B) and later the light from point A (since M' is now farther than M from point A) As a consequence M' can say the lightning strikes were not simultaneous.
>
> Note that the closing speed of the light coming from A arriving at M' is c-v (which does not mean the light is received at that speed). Also the closing speed of the light coming from point B arriving at M' is c+v (which again does not mean the light is received at that speed). Observer M', as the second postulate requires receives the light, which is moving at speed c, but at different locations relative to the emission of the lights.

Right. That experiment is ONLY about light traveling at c from different DISTANCES.
The light IS received at c+v and c-v, but that FACT has NOTHING to do with the
thought experiment, so why mention it?

Ed

El lunes, 11 de julio de 2022 a las 12:33:38 UTC-4, det...@outlook.com escribió:
> On Monday, July 11, 2022 at 9:46:18 AM UTC-5, Paparios wrote:

> > Well, you should review your knowledge about it. Einstein himself explained this in chapter 9 of his 1920 book (see https://www.bartleby.com/173/9..html).
> > There we have a train and an embankment, with observers M' and M. The train is moving, relative to the embankment, at speed v. Just when both M and M' coincide at the train station, two lightning strikes simultaneously occur at points A and B (which are equidistant from observer M). Of course the light from those lightning strikes travels in all directions at speed c. Observer M receives the lights at the same time. Observer M', moving to the right at speed v, receives first the light coming from point B (since M' is now closer than M to point B) and later the light from point A (since M' is now farther than M from point A) As a consequence M' can say the lightning strikes were not simultaneous.
> >
> > Note that the closing speed of the light coming from A arriving at M' is c-v (which does not mean the light is received at that speed). Also the closing speed of the light coming from point B arriving at M' is c+v (which again does not mean the light is received at that speed). Observer M', as the second postulate requires receives the light, which is moving at speed c, but at different locations relative to the emission of the lights.

> Right. That experiment is ONLY about light traveling at c from different DISTANCES.
> The light IS received at c+v and c-v, but that FACT has NOTHING to do with the
> thought experiment, so why mention it?
>

But the light IS NOT RECEIVED at c+v and c-v.

The lightning strikes, for observer M', travel at speed c (independently of the embankment or the train as the second postulate requires).

Observer M', at the reception of the light is at a different location (due to its speed v) relative to the observer M. So M' FINDS the light coming at speed c from point B before the light coming at speed c from point A. In both cases the light arrives to M' at speed c.

On 7/11/2022 12:33 PM, Ed Lake wrote:

> The light IS received at c+v and c-v, but that FACT has NOTHING to do with the
> thought experiment, so why mention it?
>

Why do you claim your belief is a fact?

On Sunday, July 10, 2022 at 9:50:47 AM UTC-7, det...@outlook.com wrote:
> Has any experiment ever verified "length contraction"?

Yes, in fact every aspect of special relativity has been thoroughly tested and confirmed experimentally. For example, the arms of a Michelson interferometer undergo measurable length contraction. Furthermore, special relativity would be logically self-contradictory without all three ingredients.

> The "skew of simultaneity" is certainly part of Relativity, but "the skew of
> simultaneity" is mostly about what might be called "optical illusions."

No, this is actually the aspect of special relativity for which Einstein was most famous, i.e., the realization that two events that are simultaneous in terms of one standard system of inertial coordinates are not simultaneous in terms of another. This is not any kind of illusion, it is a verifiable (and verified) objective fact.

> Time Dilation is the only NEW DISCOVERY explained in Einstein's paper.

To the contrary, Lorentz already had time dilation by 1892. Again, the startling insight that Einstein was most credited with was the relativity of simultaneity… although even this was *implicit* in Lorentz’s earlier work. Lorentz admitted that he had not fully appreciated it until Einstein pointed out the reciprocal skew of simultaneity explicitly, reconciling it with the principle of relativity.

> However, light can be RECEIVED at c+v or c-v if the RECEIVER is moving at v toward or away from the emitter. If you want to call it "the closing speed," that doesn't change anything.

Prior to the discovery of special relativity, it was thought that there is no difference between relative speed and closing speed, but special relativity revealed that there is a difference, and when you talk about light being *received* at a certain speed by an object, unless you specify otherwise, you are interpreted to be referring to the relative speed, not the closing speed.

> When radar guns measure the speed of an oncoming vehicle, they measure the "closing speed."

No, they measure the relative speed, not the closing speed. For example, if two spaceships are directly approaching each other, one moving to the left at 0.6c and the other moving to the right at 0.6c (both in terms of the Sun’s inertial coordinate system), the closing speed is 1.2c, but the relative speed between the rockets is 0.88235c, and this is what a radar gun pointed from one at the other would read.

For the range of speeds of automobiles, etc., the difference between closing speed and relative speed is imperceptibly small, but experiments have been conducted using high speed particles that emit light, moving toward and away from the receiver, and the exact predictions of special relativity have been confirmed, i.e., the speed implied by the measured Doppler frequency shift is the relative speed, not the closing speed. Do you understand this now?

> The light IS received at c+v and c-v...

Per the above, your opinion has been thoroughly debunked by the facts. Agreed?

Le 11/07/2022 à 20:49, Stan Fultoni a écrit :

>> The light IS received at c+v and c-v...
>
> Per the above, your opinion has been thoroughly debunked by the facts. Agreed?

There is an ignorance among most human beings of the fact that
relativistic velocities (ie very high velocities) do not add up in a
simple way.

Let's take the example of a right-angled triangle, we have one side which
is 4 meters, and the other which is 3 meters. If we ask a person who has
never done mathematics, what is the length of the diagonal, he will
perhaps answer hastily 7m.

But, that's not how it works. The diagonal, all mathematicians know it,
and they call it a hypotenuse, is 5m, not 7m.

The same is true for additions of relativistic velocities.

We cannot add like that not only without knowing the angles, but also
without knowing that space and time have their own physical properties if
we go very fast or if we go very far.

There is a general law of addition of velocities that encompasses all of
them, as well as all possible and imaginable angles.

The formula is here.

Note that for low speeds, this amounts to Newtonian kinetics.

We will also notice that for relativistic velocities, we can never exceed
c.

Thank you for your attention.

<http://news2.nemoweb.net/jntp?UD74f-fodxvA4cqVUSrlWPj0Av0@jntp/Data.Media:1>

R.H.

--
"Mais ne nous trompons pas.
Il n'y a pas que de la violence avec des armes : il y a des situations de
violence."
Abbé Pierre.
<http://news2.nemoweb.net/?DataID=UD74f-fodxvA4cqVUSrlWPj0Av0@jntp>

On Monday, July 11, 2022 at 12:17:43 PM UTC-5, Paparios wrote:
> El lunes, 11 de julio de 2022 a las 12:33:38 UTC-4, escribió:
> > On Monday, July 11, 2022 at 9:46:18 AM UTC-5, Paparios wrote:
>
> > > Well, you should review your knowledge about it. Einstein himself explained this in chapter 9 of his 1920 book (see https://www.bartleby.com/173/9.html).
> > > There we have a train and an embankment, with observers M' and M. The train is moving, relative to the embankment, at speed v. Just when both M and M' coincide at the train station, two lightning strikes simultaneously occur at points A and B (which are equidistant from observer M). Of course the light from those lightning strikes travels in all directions at speed c.. Observer M receives the lights at the same time. Observer M', moving to the right at speed v, receives first the light coming from point B (since M' is now closer than M to point B) and later the light from point A (since M' is now farther than M from point A) As a consequence M' can say the lightning strikes were not simultaneous.
> > >
> > > Note that the closing speed of the light coming from A arriving at M' is c-v (which does not mean the light is received at that speed). Also the closing speed of the light coming from point B arriving at M' is c+v (which again does not mean the light is received at that speed). Observer M', as the second postulate requires receives the light, which is moving at speed c, but at different locations relative to the emission of the lights.
>
> > Right. That experiment is ONLY about light traveling at c from different DISTANCES.
> > The light IS received at c+v and c-v, but that FACT has NOTHING to do with the
> > thought experiment, so why mention it?
> >
> But the light IS NOT RECEIVED at c+v and c-v.

Of course it is. M' is a MOVING RECEIVER.
> The lightning strikes, for observer M', travel at speed c (independently of the embankment or the train as the second postulate requires).

Yes, the light travels at c.

> Observer M', at the reception of the light is at a different location (due to its speed v) relative to the observer M. So M' FINDS the light coming at speed c from point B before the light coming at speed c from point A. In both cases the light arrives to M' at speed c.

NO! M' receives the light at c+v from the strike in front of him, and at c-v
from the strike behind him. That doesn't change the fact that the light
from the two strikes does not arrive simultaneously as it did for M.
The speed at which M' is traveling creates v but it doesn't change c.

M' moved 100 feet closer to point A when he received the light from A,
and he moved 200 feet farther from point B when he receive the light
from B. M was stationary, so he received light from both strikes at the
same time. The fact that M' received the light form point A at c+v
doesn't mean that the light TRAVELED at c+v, it means that the light
was traveling at c and M' was traveling at v when he met the light.

Ed

On 7/11/2022 12:20 PM, Ed Lake wrote:
> On Monday, July 11, 2022 at 7:17:38 AM UTC-5, Ufonaut wrote:
>> On Monday, July 11, 2022 at 1:58:08 AM UTC+10, wrote:
>>> On Sunday, July 10, 2022 at 8:35:04 AM UTC-5, Ufonaut wrote:
>>>> On Sunday, July 10, 2022 at 2:05:20 AM UTC+10, wrote:
>>>>> On Saturday, July 9, 2022 at 10:36:41 AM UTC-5, Paparios wrote:
>>>>>> El sábado, 9 de julio de 2022 a las 10:41:19 UTC-4, escribió:
>>>>>>> On Friday, July 8, 2022 at 4:56:44 PM UTC-5, RichD wrote:
>>>>>>>> On July 8, RichD wrote:
>>>>>>>>>>>> The Second Postulate is: "light is always propagated in empty
>>>>>>>>>>>> space with a definite velocity c which is independent of the state of motion
>>>>>>>>>>>> of the EMITTING body."
>>>>>>>>>
>>>>>>>>>>> It's quite obvious it means the receiver/observer (in this case the
>>>>>>>>>>> front of the car) will receive the photon at c, regardless of the motion
>>>>>>>>>>> or lack thereof of the photon's source (radar gun).
>>>>>>
>>>>>>> WRONG! It says the EMITTER always EMITS light at c. Einstein's Second
>>>>>>> Postulate says absolutely NOTHING about what a RECEIVER/OBSERVER will see.
>>>>>> Again you do not understand English. That introduction says:
>>>>>> "light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body".
>>>>> Agreed.
>>>>>>
>>>>>> The "state of motion of the emitting body" clearly means either the body is stationary or the body is moving. Therefore, a) if the emitter is stationary, light will propagate at speed c. b) If the emitter is moving, light will also propagate at speed c.
>>>>> Agreed.
>>>>>>
>>>>>> Say the emitter is at point E and the receiver is at point R.
>>>>>>
>>>>>> Case 1) Both E and R are stationary E.....c-->.......................R E emits at speed c, R receives at speed c.
>>>>> Agreed.
>>>>>> Case 2) E is moving at speed v, R is stationary, E emits light at speed c, R receives the light at speed c.
>>>>> Agreed.
>>>>>> Case 3) E is stationary, R is moving towards E at speed w. E emits light at speed c, R receives the light at speed V=(c+w)/(1+w/c)=c
>>>>>> (see equations in section 5 of the paper).
>>>>>>
>>>>>> Therefore in all cases, the receiver R receives the light at speed c.
>>>>> Nonsense. Section 5 of Einstein's paper says, "It follows, further,
>>>>> that the velocity of light c cannot be altered by composition
>>>>> with a velocity less than that of light." In other words, when an
>>>>> observer receives light at c+v, v is his speed and c is still the speed
>>>>> of light.
>>>> Except this contradicts your earlier statement :
>>>> On Sunday, July 10, 2022 at 12:41:19 AM UTC+10, wrote:
>>>>> A RECEIVER or observer will observe light as moving at c+v if
>>>>> the receiver is moving toward the emitter at speed v, and at c-v if the receiver
>>>>> is moving away from the emitter at speed v.
>>> How do those statements disagree? They say the SAME THING.
>>>> So for an emitter moving at speed w, and a receiver keeping an unchanging distance away - ie, w " is his speed" and also therefore the v of your quote here "moving toward the emitter at speed v" is = 0), then "A RECEIVER or observer will observe light as moving at c+v" = c+0 = c, so NOT at c+w.
>>> If the emitter and receiver are moving together at the same speed,
>>> their relative speed is zero. Light will be emitted at c and will be
>>> received at c.
>>>
>>> If the emitter and receiver are NOT moving together at the same speed,
>>> the emitter will still emit light at c, but the receiver will receive that light
>>> at c+v or c-v depending on his speed relative to the emitter.
>> OK, Let’s look at Case 2 above : “Case 2) E is moving at speed v, R is stationary,” - so “the emitter and receiver are NOT moving together at the same speed”, there is a relative velocity v between them.
>
> Correct.
>
>>
>> Which means you are saying BOTH that “R receives the light at speed c. > > > Agreed. “ (so NOT at c+v or c-v)
>> AND ALSO “the receiver will receive that light at c+v or c-v depending on his speed relative to the emitter.”
>
> No. The receiver is stationary.

With respect to what?

> Only the emitter is moving.

With respect to what?

All motion is relative to another frame (or object if you prefer).

This isn't even Einstein, this is Galileo, 400 years ago.

I can use the emitter to be stationary, and in this case the receiver is
moving relative to it. Or I can use the receiver as stationary and the
emitter is moving relative to it. See Galileo's ship story.

> So, the emitter emits light at c even though the emitter is moving.

Relative to what?

> The receiver is stationary

Relative to what?

> and receives the light at c.
>
> The emitter is moving relative to the receiver. The receiver is STATIONARY,
> which means the receiver is NOT moving.

You don't define any "relative to" at all here. Again, nothing to do
with Einstein, this is Galileo and Newton.

> The FACT that the receiver
> receives the light at c confirms that the receiver is not moving.

How so? Remember the second postulates states the receiver ALWAYS
receives the light at c, as long as it is inertial.

> It also says that you cannot simply decide that the receiver is moving and
> the emitter is stationary, because the FACT that the receiver receives the
> light at c PROVES that the receiver is stationary.

Possibly proves it as inertial, but you don't state stationary relative
to anything.

>> So do you have ANY basis for the claim that such absolute points exist ?
>
> Yes. When we receive light, it comes in a straight line from the stationary
> point where it was emitted. When we look at Proxima Centauri, we see it
> where it WAS two years ago. It is now millions of miles away from that point.

In which frame do you define that point? In the frame of Proxima
Centauri, it is right there, still at Proxima Centauri. (assume inertial
motion)

You still seem to try to define some "absolutely stationary" frame, and
remember, a frame with special properties like that violates the first
postulate.

Don't forget Einstein EXPLICITLY stated motion cannot be assigned to a
point in empty space.

> If you trace a photon back to where it originated, it originated at a stationary
> point in space

In our frame, maybe. You don't specify either a frame or an object
considered stationary (defining said frame).

> where the emitter happened to be when it emitted the photon.

As seen in our/the observer's frame.
>
>>> All you can do is measure the speed of
>>> one emitting atom versus another.
>>
>>> The International Space Station (ISS) is moving at 17,400 mph relative to the
>>> surface of the earth. Relative to the surface of the sun, the ISS is ALSO moving
>>> at 67,000 mph. Relative to the center of the Milky Way galaxy, the ISS is ALSO
>>> moving at 560,000 mph.

>> My point exactly. As you have been told many times, there is only relative motion. All motion is RELATIVE, not absolute - and therefore cannot give rise to absolute effects (such as an absolute one-way time dilation).
>
> All motion is relative to the speed of light.

Nope. All motion is relative to some frame.
You shouldn't present your OPINIONS as factual. They're opinions.

> Because the speed of light is the fastest
> speed possible in our universe, all other speeds are a PERCENTAGE of the speed
> of light.

Relative to something.
>
> 17,400 mph
> is 0.0025946269802424% of the speed of light.

Relative to what? An astronaut on the ISS?

> 67,000 mph
> is 0.0099908050388646% of the speed of light.

Relative to what?

> 560,000 mph
> is 0.083505236145734% of the speed of light.

Relative to what?

>
> Motion is SEEN as relative when I move away from you or when you move away
> from me, but only ONE of us is moving at a greater percentage of the speed of light.

Relative to what? (and speeds cannot be "relative to the speed of light"
without providing a reference frame of some sort. Physicists may say a
subatomic particle is moving at 90% of the speed of light, but that is
going to be relative to the lab.
>>>
>>> You ask about "a space station that is stationary relative to the sun." There
>>> is no such thing. If it was not moving, the ISS would be pulled into the sun by
>>> the sun's gravity.
>> “a space station stationary relative to the sun” is clearly not referring to the ISS, but is a hypothetical.
>>
>> OK, such a space station would eventually fall into the sun - but we can still perfectly validly consider the effects of Special Relativity over a SHORT period of time (so the amount of pulling is negligible). During such a time, which would you say is moving - that (hypothetical) space station, or the earth in its orbit ?
>
> The ISS is moving in its orbit around the earth. The earth is moving in its orbit
> around the sun. The sun is moving in its orbit around the center of the Milky Way
> galaxy. NOTHING is stationary.

On Monday, July 11, 2022 at 1:06:31 PM UTC-5, Volney wrote:
> On 7/11/2022 12:33 PM, Ed Lake wrote:
>
> > The light IS received at c+v and c-v, but that FACT has NOTHING to do with the
> > thought experiment, so why mention it?
> >
> Why do you claim your belief is a fact?

Because it is verified by MANY EXPERIMENTS.
The list: http://www.ed-lake.com/Variable-Speed-of-Light-Experiments.html

Ed