dono incited me to ask such a question.

In the recent thread entitled "addition of velocities", the op
inquired about closing speeds.

An aggressive debate ensued.

I (and others) maintained that closing speed (of two things)
is simply "v1 ± v2" [depending of the sign conventions].
Or, the rate of change of the separation (distance) between the two things.
[We were discussing trajectories along the x_axis only btw].

Dono however, maintains that the above are not the meaning of closing speed as used here (relativity and kinematics in general). And he reasons that:

"v1+v2 is the closing speed of two objects that STARTED SIMULTANEOSLY. "

" If the two objects don't start simultaneously, one cannot define closing speed."

I am wondering as to what is the consensus here concerning the concept of
"closing speed".

On Thursday, September 29, 2022 at 7:35:14 PM UTC-7, rotchm wrote:
> dono incited me to ask such a question.
>
> In the recent thread entitled "addition of velocities", the op
> inquired about closing speeds.
>
> An aggressive debate ensued.
>
> I (and others) maintained that closing speed (of two things)
> is simply "v1 ± v2" [depending of the sign conventions].
Well, you are an idiot, Stephane.
Time has made this only worse.
Closing speed is a convention, used to express the rate at which two objects, starting simultaneously, cover a distance L between them:

v1*t+v2*t=L (see, "t" needs to be the SAME)
t=L/(v1+v2)

By CONVENTION, UNDER the above conditions, u=v1+v2 is called closing speed
The concept is very useful when one of the "objects" is a pulse of light, say v1=c. Then the closing speed of covering a distance "L" is c+v. But cranks, of the type of Thomas Heger and Stephane Baune, call this "relative speed of light". This causes infinitely long debates about light speed not being constant. Most of such debates center around Einstein derivation of the Lorentz transforms in "On the Electrodynamics..." but also in the derivation of the phase difference in the Sagnac experiments where cranks like Stephane Baune will claim that light goes around at c+v in one direction and c-v in the opposite direction. Ergo, the Sagnac effect is "proof" that light speed is "variable".

On Thursday, September 29, 2022 at 10:44:29 PM UTC-4, Dono. wrote:
> On Thursday, September 29, 2022 at 7:35:14 PM UTC-7, rotchm wrote:

> Closing speed is a convention, used to express the rate at which two objects,

Finally, you agree to that part (you denied this in the previous thread). Good.

> starting simultaneously,

Simultaneity has nothing to do with it.
> v1*t+v2*t=L

That is not the definition of closing speed.

> (see, "t" needs to be the SAME)

Yes that is what I told you.
Remember, I told you: At time t, the closing speed of two things is the "sum" of their speeds at that time: "v1 + v2".
You denied that.

> t=L/(v1+v2)
>
> By CONVENTION, UNDER the above conditions, u=v1+v2 is called closing speed

Finally we are getting somewhere in this thread...
Yes under the above conditions it is the closing speed.
In the general conditions, closing speed is v1 + v2, including in your above conditions.
No matter when or how to objects initiated their motion, at a given time, they have a closing speed which is
v1 + v2 at that time in question.

In the scenario that initiated this discussion, two bullets were approaching each other with speeds v1 & v2.
The closing speed is v1 + v2, no matter when these bullets were fired. So you finally agree to this!?

> The concept is very useful when one of the "objects" is a pulse of light, say v1=c. Then the closing speed of covering a distance "L" is c+v.

The closing speed between light and an object with speed v wrt a given reference frame is c ± v, independently
when these things initiated their motion.

So it looks like as to not make a fool of yourself in this thread, you finally agree (mostly)
with me & Stan.

On Thursday, September 29, 2022 at 8:33:39 PM UTC-7, rotchm wrote:
> On Thursday, September 29, 2022 at 10:44:29 PM UTC-4, Dono. wrote:
> > On Thursday, September 29, 2022 at 7:35:14 PM UTC-7, rotchm wrote:
>
> > Closing speed is a convention, used to express the rate at which two objects,
> Finally, you agree to that part (you denied this in the previous thread). Good.
>
> > starting simultaneously,
>
> Simultaneity has nothing to do with it.
>

That is because you are an imbecile who is incapable to follow how the concept is derived, Stephane.

> > v1*t+v2*t=L
>
> That is not the definition of closing speed.

Actually , it is. But you are too much of an imbecile to be able to follow it.

On Thursday, September 29, 2022 at 11:45:50 PM UTC-4, Dono. wrote:
> On Thursday, September 29, 2022 at 8:33:39 PM UTC-7, rotchm wrote:
> > On Thursday, September 29, 2022 at 10:44:29 PM UTC-4, Dono. wrote:
> > > On Thursday, September 29, 2022 at 7:35:14 PM UTC-7, rotchm wrote:

> > > v1*t+v2*t=L
> >
> > That is not the definition of closing speed.
> Actually , it is.

Ok, let's see. At time t =0 your definition says
0=L which is the initial seperation, the length of the ship. Mighty good definition you have there!

And at time t= 0.01 say, do the two bullets have a closing speed (wrt ship frame)?

On Thursday, September 29, 2022 at 9:01:44 PM UTC-7, rotchm wrote:
> On Thursday, September 29, 2022 at 11:45:50 PM UTC-4, Dono. wrote:
> > On Thursday, September 29, 2022 at 8:33:39 PM UTC-7, rotchm wrote:
> > > On Thursday, September 29, 2022 at 10:44:29 PM UTC-4, Dono. wrote:
> > > > On Thursday, September 29, 2022 at 7:35:14 PM UTC-7, rotchm wrote:
>
> > > > v1*t+v2*t=L
> > >
> > > That is not the definition of closing speed.
> > Actually , it is.
> Ok, let's see. At time t =0 your definition says
> 0=L which is the initial seperation, the length of the ship. Mighty good definition you have there!
>
> And at time t= 0.01 say, do the two bullets have a closing speed (wrt ship frame)?
Idiot,

"t" is the time when the two objects meet. You have outdone yourself , Stephane. Congratulations, bozo!

On Friday, September 30, 2022 at 12:12:50 AM UTC-4, Dono. wrote:
> On Thursday, September 29, 2022 at 9:01:44 PM UTC-7, rotchm wrote:
> > On Thursday, September 29, 2022 at 11:45:50 PM UTC-4, Dono. wrote:
> > > On Thursday, September 29, 2022 at 8:33:39 PM UTC-7, rotchm wrote:
> > > > On Thursday, September 29, 2022 at 10:44:29 PM UTC-4, Dono. wrote:
> > > > > On Thursday, September 29, 2022 at 7:35:14 PM UTC-7, rotchm wrote:
> >
> > > > > v1*t+v2*t=L
> > > >
> > > > That is not the definition of closing speed.
> > > Actually , it is.
> > Ok, let's see. At time t =0 your definition says
> > 0=L which is the initial seperation, the length of the ship. Mighty good definition you have there!
> >
> > And at time t= 0.01 say, do the two bullets have a closing speed (wrt ship frame)?
> Idiot,
>
> "t" is the time when the two objects meet. You have outdone yourself , Stephane. Congratulations, bozo!

You are the bozo here since you did not realize what happened. You cornered yourself again.

You are saying now that closing speed depends on the time at which two objects coincide.

Of course you can use the concept of closing speed to find out which time to object coincide, but that is not the definition of closing speed. The definition of closing speed is independent when the objects were set in motion, and when objects coincide if they do.

For instance, consider two objects leaving each other in separate directions. What is their closing speed at time t?

On Thursday, September 29, 2022 at 8:33:39 PM UTC-7, rotchm wrote:
> > starting simultaneously,
>
> Simultaneity has nothing to do with it.

To be clear, two objects with positions x1(t) and x2(t) have the closing speed V(t) = dx1(t)/dt - dx2(t)/dt at time t in terms of S, and in terms of another system S' the closing speed is V'(t') = dx1'(t')/dt' - dx2'(t')/dt' at a given time t'. Obviously the relevant simultaneity (equal t or equal t') is built into this definition, as it is also built into the speed composition formula that lets us weite these as v1-v2 and v1'-v2'. Needless to say, whether or not the objects started simultaneously is irrelevant, as is the distance between them, given only the stipulation that they are both in flight with specified speeds in a specified order.

On Thursday, September 29, 2022 at 9:19:13 PM UTC-7, rotchm wrote:
> On Friday, September 30, 2022 at 12:12:50 AM UTC-4, Dono. wrote:
> > On Thursday, September 29, 2022 at 9:01:44 PM UTC-7, rotchm wrote:
> > > On Thursday, September 29, 2022 at 11:45:50 PM UTC-4, Dono. wrote:
> > > > On Thursday, September 29, 2022 at 8:33:39 PM UTC-7, rotchm wrote:
> > > > > On Thursday, September 29, 2022 at 10:44:29 PM UTC-4, Dono. wrote:
> > > > > > On Thursday, September 29, 2022 at 7:35:14 PM UTC-7, rotchm wrote:
> > >
> > > > > > v1*t+v2*t=L
> > > > >
> > > > > That is not the definition of closing speed.
> > > > Actually , it is.
> > > Ok, let's see. At time t =0 your definition says
> > > 0=L which is the initial seperation, the length of the ship. Mighty good definition you have there!
> > >
> > > And at time t= 0.01 say, do the two bullets have a closing speed (wrt ship frame)?
> > Idiot,
> >
> > "t" is the time when the two objects meet. You have outdone yourself , Stephane. Congratulations, bozo!

> You are saying now that closing speed depends on the time at which two objects coincide.
>

Just when I thought you reached bottom, Stephane, you managed to dig yourself even deeper. You are starting to give Ken Seto competition for the village idiot title. Thanks for the entertainment, dumbestfuck!

> For instance, consider two objects leaving each other in separate directions. What is their closing speed at time t?

This is even better than the prior one. You are getting more imbecillic by the post.

On Thursday, September 29, 2022 at 10:35:14 PM UTC-4, rotchm wrote:
> dono incited me to ask such a question.
>
> In the recent thread entitled "addition of velocities", the op
> inquired about closing speeds.
>
> An aggressive debate ensued.
>
> I (and others) maintained that closing speed (of two things)
> is simply "v1 ± v2" [depending of the sign conventions].
> Or, the rate of change of the separation (distance) between the two things.
> [We were discussing trajectories along the x_axis only btw].

In SR closing speed is viewed from an outside observer. As viewed by an observer who receives the incoming light, the closing speed of light is c.
>
> Dono however, maintains that the above are not the meaning of closing speed as used here (relativity and kinematics in general). And he reasons that:
>
> "v1+v2 is the closing speed of two objects that STARTED SIMULTANEOSLY. "
>
> " If the two objects don't start simultaneously, one cannot define closing speed."
>
> I am wondering as to what is the consensus here concerning the concept of
> "closing speed".

On Thursday, September 29, 2022 at 7:35:14 PM UTC-7, rotchm wrote:
> dono incited me to ask such a question.
>
> In the recent thread entitled "addition of velocities", the op
> inquired about closing speeds.
>
> An aggressive debate ensued.
>
> I (and others) maintained that closing speed (of two things)
> is simply "v1 ± v2" [depending of the sign conventions].
> Or, the rate of change of the separation (distance) between the two things.
> [We were discussing trajectories along the x_axis only btw].
>
> Dono however, maintains that the above are not the meaning of closing speed as used here (relativity and kinematics in general). And he reasons that:
>
> "v1+v2 is the closing speed of two objects that STARTED SIMULTANEOSLY. "
>
> " If the two objects don't start simultaneously, one cannot define closing speed."
>
> I am wondering as to what is the consensus here concerning the concept of
> "closing speed".
The fundamental property of closing velocity consists in the fact that two observers in motion wrt each other will each calculate identical displacements wrt each other during identical time intervals.

On Friday, September 30, 2022 at 11:00:48 AM UTC-4, patdolan wrote:

> The fundamental property of closing velocity consists in the fact that two observers in motion wrt each other
> will each calculate identical displacements wrt each other during identical time intervals.

Whats the definition of closing speed then?
Whats its "formula" ?
An example ?

Le 30/09/2022 à 16:27, Ken Seto a écrit :

> the closing speed of light is c.

<http://news2.nemoweb.net/jntp?6bjgLCUEIoCkHZ8jo5ZdMFC_27Y@jntp/Data.Media:1>

R.H.

On Friday, September 30, 2022 at 11:29:02 AM UTC-4, Richard Hachel wrote:
> Le 30/09/2022 à 16:27, Ken Seto a écrit :
>
> > the closing speed of light is c.
> <http://news2.nemoweb.net/jntp?6bjgLCUEIoCkHZ8jo5ZdMFC_27Y@jntp/Data.Media:1>

Link doesn't work.

On Friday, September 30, 2022 at 8:25:25 AM UTC-7, rotchm wrote:
> On Friday, September 30, 2022 at 11:00:48 AM UTC-4, patdolan wrote:
>
> > The fundamental property of closing velocity consists in the fact that two observers in motion wrt each other
> > will each calculate identical displacements wrt each other during identical time intervals.
> Whats the definition of closing speed then?
> Whats its "formula" ?
> An example ?
Excellent question, oh man of the miniature biceps. The formulation of closing velocity is an entirely different situation in a Galilean Universe vs. and Einsteinian one. We have been over this before. Add another 10 lbs to your curling bar and see if that helps.

On Friday, September 30, 2022 at 11:22:33 AM UTC-7, patdolan wrote:
> On Friday, September 30, 2022 at 8:25:25 AM UTC-7, rotchm wrote:
> > On Friday, September 30, 2022 at 11:00:48 AM UTC-4, patdolan wrote:
> >
> > > The fundamental property of closing velocity consists in the fact that two observers in motion wrt each other
> > > will each calculate identical displacements wrt each other during identical time intervals.
> > Whats the definition of closing speed then?
> > Whats its "formula" ?
> > An example ?
> Excellent question, oh man of the miniature biceps. The formulation of closing velocity is an entirely different situation in a Galilean Universe vs.. and Einsteinian one. We have been over this before. Add another 10 lbs to your curling bar and see if that helps.

I shall deign to help you out a bit rotchm, and provide you the formula you crave.

In the case of observer O and observer O', the closing of v must be equivalent to closing velocity v' if the Dolan condition on closing velocity is to hold true

"The fundamental property of closing velocity consists in the fact that two observers in motion wrt each other will each calculate identical displacements wrt each other during identical time intervals."

Therefore, if v == v' then ∆x/∆t == ∆x'/∆t'. This last equality is true enough when it comes to the speed of light, and is the very expression of the second postulate. But it must also be true for ALL closing velocities less than c.

rotchm, use the LTs to solve for v' in terms of v by taking the ratio of ∆x'/∆t'. Then show us what you find. Do this immediately..

On Friday, September 30, 2022 at 1:35:18 PM UTC-7, patdolan wrote:

> "The fundamental property of closing velocity consists in the fact that two observers in motion wrt each other will each calculate identical displacements wrt each other during identical time intervals."

2 observers in motion wrt each other can *never* measure their closing speed, and what they *do* measure is always less than c.

On Friday, September 30, 2022 at 4:35:18 PM UTC-4, patdolan wrote:
> On Friday, September 30, 2022 at 11:22:33 AM UTC-7, patdolan wrote:
> > On Friday, September 30, 2022 at 8:25:25 AM UTC-7, rotchm wrote:

> > > Whats the definition of closing speed then?

No answer?

> > > Whats its "formula" ?

No answer?

> > Excellent question, oh man of the miniature biceps. The formulation of closing velocity is an entirely different
> > situation in a Galilean Universe vs. and Einsteinian one.

Really? Is not closing speed of two things the "difference" of their speeds as measured in a chosed frame?
"v1-v2" ?

> In the case of observer O and observer O', the closing of v must

"the closing of v" makes no sense, its gibberish. You mean the closing speed of two "things", not of v.
You definitely need to learn to write coherently in English.

> be equivalent to closing velocity v' if the Dolan condition on closing velocity is to hold true

Off topic. We are not discussing any dolan conditions. We are discussing the notion of closing speed as used in physics, in SR.
Not your physics not somebody else's Theory or anything else.

> "The fundamental property of closing velocity

I asked about closing speed not closing velocity.
Re-read the op.

< rest of irrelevancies snipped>

On Friday, September 30, 2022 at 6:59:56 PM UTC-4, Paul Alsing wrote:
> On Friday, September 30, 2022 at 1:35:18 PM UTC-7, patdolan wrote:
>
> > "The fundamental property of closing velocity consists in the fact that two observers in motion wrt each other will each calculate identical displacements wrt each other during identical time intervals."
> 2 observers in motion wrt each other can *never* measure their closing speed, and what they *do* measure is always less than c.

Since you talked about closing speeds, can you explain what you mean by such an expression?
That is, according to you, what is the definition of closing speed as used in physics/SR?

On Friday, September 30, 2022 at 4:51:03 PM UTC-7, rotchm wrote:
> On Friday, September 30, 2022 at 4:35:18 PM UTC-4, patdolan wrote:
> > On Friday, September 30, 2022 at 11:22:33 AM UTC-7, patdolan wrote:
> > > On Friday, September 30, 2022 at 8:25:25 AM UTC-7, rotchm wrote:
>
> > > > Whats the definition of closing speed then?
> No answer?
>
> > > > Whats its "formula" ?
>
> No answer?
> > > Excellent question, oh man of the miniature biceps. The formulation of closing velocity is an entirely different
> > > situation in a Galilean Universe vs. and Einsteinian one.
> Really? Is not closing speed of two things the "difference" of their speeds as measured in a chosed frame?
Oh you fool rotchm. You fool! There are no "two speeds". You might as well say that there is only one closing speed, and the other is at rest. Or there are three closing speeds: the speed of one - (the speed of an FoR in which the other is traveling at yet another speed) or there are 100 speeds....This is called the "Principle of Relativity" which states there are no preferred combinations of speeds--they all combine to the same quantity.

The Dolan Condition is the only common sensical approach to closing speed in and Einsteineite universe. If you had my physics critical theory and deconstruction skills, rotchm, you would also realize that the DC is also the death knell of SR. Now do the derivation you were assigned so that we can get on with your education.

> "v1-v2" ?
> > In the case of observer O and observer O', the closing of v must
> "the closing of v" makes no sense, its gibberish. You mean the closing speed of two "things", not of v.
> You definitely need to learn to write coherently in English.
> > be equivalent to closing velocity v' if the Dolan condition on closing velocity is to hold true
> Off topic. We are not discussing any dolan conditions. We are discussing the notion of closing speed as used in physics, in SR.
> Not your physics not somebody else's Theory or anything else.
> > "The fundamental property of closing velocity
> I asked about closing speed not closing velocity.
> Re-read the op.
>
> < rest of irrelevancies snipped>

On Friday, September 30, 2022 at 4:53:48 PM UTC-7, rotchm wrote:
> On Friday, September 30, 2022 at 6:59:56 PM UTC-4, Paul Alsing wrote:
> > On Friday, September 30, 2022 at 1:35:18 PM UTC-7, patdolan wrote:
> >
> > > "The fundamental property of closing velocity consists in the fact that two observers in motion wrt each other will each calculate identical displacements wrt each other during identical time intervals."
> > 2 observers in motion wrt each other can *never* measure their closing speed, and what they *do* measure is always less than c.
> Since you talked about closing speeds, can you explain what you mean by such an expression?
> That is, according to you, what is the definition of closing speed as used in physics/SR?
Yes, this is a silly string of words, to be sure. A lot of people in Oregon and California do that a lot.

On Friday, September 30, 2022 at 4:51:03 PM UTC-7, rotchm wrote:
> On Friday, September 30, 2022 at 4:35:18 PM UTC-4, patdolan wrote:
> > On Friday, September 30, 2022 at 11:22:33 AM UTC-7, patdolan wrote:
> > > On Friday, September 30, 2022 at 8:25:25 AM UTC-7, rotchm wrote:
>
> > > > Whats the definition of closing speed then?
> No answer?
>
> > > > Whats its "formula" ?
>
> No answer?
> > > Excellent question, oh man of the miniature biceps. The formulation of closing velocity is an entirely different
> > > situation in a Galilean Universe vs. and Einsteinian one.
> Really? Is not closing speed of two things the "difference" of their speeds as measured in a chosed frame?
> "v1-v2" ?
> > In the case of observer O and observer O', the closing of v must
> "the closing of v" makes no sense, its gibberish. You mean the closing speed of two "things", not of v.
> You definitely need to learn to write coherently in English.
> > be equivalent to closing velocity v' if the Dolan condition on closing velocity is to hold true
> Off topic. We are not discussing any dolan conditions. We are discussing the notion of closing speed as used in physics, in SR.
> Not your physics not somebody else's Theory or anything else.
> > "The fundamental property of closing velocity
> I asked about closing speed not closing velocity.
> Re-read the op.
>
> < rest of irrelevancies snipped>
The Einstein velocity addition formula makes a mockery of a well defined closing speed for all FoRs other than the co-moving frame of precisely *one* of the objects. And that object must consider itself at rest in it's own FoR while measuring the closing speed of the other object. This is Dolativity 101.

On Friday, September 30, 2022 at 3:59:56 PM UTC-7, Paul Alsing wrote:
> On Friday, September 30, 2022 at 1:35:18 PM UTC-7, patdolan wrote:
>
> > "The fundamental property of closing velocity consists in the fact that two observers in motion wrt each other will each calculate identical displacements wrt each other during identical time intervals."
> 2 observers in motion wrt each other can *never* measure their closing speed, and what they *do* measure is always less than c.

Who measured that paul. Have you got to those speeds?

On Friday, September 30, 2022 at 6:48:25 PM UTC-7, patdolan wrote:
> On Friday, September 30, 2022 at 4:51:03 PM UTC-7, rotchm wrote:
> > On Friday, September 30, 2022 at 4:35:18 PM UTC-4, patdolan wrote:
> > > On Friday, September 30, 2022 at 11:22:33 AM UTC-7, patdolan wrote:
> > > > On Friday, September 30, 2022 at 8:25:25 AM UTC-7, rotchm wrote:
> >
> > > > > Whats the definition of closing speed then?
> > No answer?
> >
> > > > > Whats its "formula" ?
> >
> > No answer?
> > > > Excellent question, oh man of the miniature biceps. The formulation of closing velocity is an entirely different
> > > > situation in a Galilean Universe vs. and Einsteinian one.
> > Really? Is not closing speed of two things the "difference" of their speeds as measured in a chosed frame?
> > "v1-v2" ?
> > > In the case of observer O and observer O', the closing of v must
> > "the closing of v" makes no sense, its gibberish. You mean the closing speed of two "things", not of v.
> > You definitely need to learn to write coherently in English.
> > > be equivalent to closing velocity v' if the Dolan condition on closing velocity is to hold true
> > Off topic. We are not discussing any dolan conditions. We are discussing the notion of closing speed as used in physics, in SR.
> > Not your physics not somebody else's Theory or anything else.
> > > "The fundamental property of closing velocity
> > I asked about closing speed not closing velocity.
> > Re-read the op.
> >
> > < rest of irrelevancies snipped>
> The Einstein velocity addition formula makes a mockery of a well defined closing speed for all FoRs other than the co-moving frame of precisely *one* of the objects. And that object must consider itself at rest in it's own FoR while measuring the closing speed of the other object. This is Dolativity 101.
The me further add to my own brilliant insight that the proper closing speed of an object, described above, is made a mockery of by its coordinate closing speed. But that is a Dolativity 400 level course.

On Friday, September 30, 2022 at 6:23:14 PM UTC-7, patdolan wrote:
> On Friday, September 30, 2022 at 4:53:48 PM UTC-7, rotchm wrote:
> > On Friday, September 30, 2022 at 6:59:56 PM UTC-4, Paul Alsing wrote:
> > > On Friday, September 30, 2022 at 1:35:18 PM UTC-7, patdolan wrote:
> > >
> > > > "The fundamental property of closing velocity consists in the fact that two observers in motion wrt each other will each calculate identical displacements wrt each other during identical time intervals."

> > > 2 observers in motion wrt each other can *never* measure their closing speed, and what they *do* measure is always less than c.

> > Since you talked about closing speeds, can you explain what you mean by such an expression?

You need to read what Uncle Ben said about this in the first post of this thread...

https://groups.google.com/g/sci.physics.relativity/c/-b3lO0V6RZg

.... in this post he says..."Closing speed is the rate of change of the distance between two objects as they both move. Closing speed is certainly a rate of change of a distance, but in the given frame of reference, there is no material object nor even a photon that moves with that speed."

Later he says...

"Consider two light beams aimed at each other, each traveling at speed c. The distance between their light fronts decreases at the rate 2c,
and this is the closing speed."

Pretty simple once you understand that this 2c measurement *must* be observed from a frame that is independent of the frames of either beam. The distance between 2 objects (or beams of light) that are approaching each other can exceed c, but no object itself can exceed c. I just do not understand why this concept is so hard to understand. If both you and I have a top running speed of, say, 20 mph, and we run directly towards each other, then we will be approaching each other at 40 mph, even though neither one of us can run that fast. Same with light beams. Of course, applying the Lorentz transformation, we could show that the 2 of us running towards each other are not actually approaching at 40 mph but something less than that... but at such low speeds it would be unmeasurable... which is why no one bothers to ever calculate approaching speeds using the Lorentz transformations! This concept is also discussed in Uncle Ben's post...