Co-Accelerating Ships: Explaining the Problem

[RandallB]

I've heard there has been some experiments with centrifuges, producing high acceleration rates on clocks, and that no time dilation has been observed. That is also good indication towards GR, but it is rather curious also because doesn't SR alone predict time dilation for such an experiment?

NO, that is not true; they DO see a time dilation. If a dilation was not seen it would be a counter indicator to Realitivity.

Muons (a very small clock) highly accelerated in the ‘centrifuge’ of a storage ring live much longer than expected. I.E. their clock is running slow compared to us observing them live longer. They just don’t use GR as the reason for this, they use SR and the speed in the ring alone to calculate the time dilation.

However, I expect if they were to ignore the SR effect and take the acceleration as an equivalent to a force of gravity as their only consideration they would get the same answer.

Lots of centrifuge examples like that. The example I’ve not seen is a direct measurement of gravity of opposing directions being combined on a clock, like at the center of the earth.

 

[pervect]

So it got me curious because such an experiment would yield completely opposite predictions from GR and emitter theory. If the clocks were indeed running slower in the center of the Earth (or in similar setup), that would be so much stronger indication towards GR than GPS clocks.

I've heard there has been some experiments with centrifuges, producing high acceleration rates on clocks, and that no time dilation has been observed. That is also good indication towards GR, but it is rather curious also because doesn't SR alone predict time dilation for such an experiment?

(btw, I don't know if there is any actual information about such emitter theory time dilation as I'm describing, or if anyone has actually tried to develop it further and seen that it doesn't lead anywhere. I haven't been able to find any information of this, unfortunately)

-Anssi

Emission theory is already dead except in the lunatic fringe.

The speed of light (gamma rays) from a very fast pi meson has actually been measured, and found to be equal to 'c' within 400 ppm.

Emission theories hold that the speed of light is dependent on its source, and are therefore falsified by this class of experiment.

http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html#moving-source tests

Alvaeger F.J.M. Farley, J. Kjellman and I Wallin, Physics Letters 12, 260 (1964).

and another experiment

Filipas and Fox, Phys. Rev. 135 no. 4B (1964), p B1071.

This in addition to astronomical observations that the fact that light from a binary star moving towards us does not arive earlier than the light from the other star that is moving away. (Some variants of emission theory suggest that extinction effects in the interstellar media could explain the binary star result, but there is no explanation in terms of extinction for the failure to measure a differing speed of light from the pi-meson experiments in terms of emission theory).

As far as centrifuge experiments go, there have been several. MTW mentions Turner & Hill's "ether drift" experiments, for instance. Details of the setup vary with the experiment being conducted, but unsuprpsingly all reproducible results are consistent with relativity.

 

[AnssiH]

NO, that is not true; they DO see a time dilation. If a dilation was not seen it would be a counter indicator to Realitivity.

Interesting... If I find some more information about this, this could mean there's one problem less on the back of the emitter theory.

-Anssi

 

[AnssiH]

Emission theory is already dead except in the lunatic fringe.

Not saying that I'm putting my money on Emitter theory rather than on Relativity but;

All theories are just abstract models. This is given by the way we handle all information in our mind only semantically. There's a good account of this in "https://www.amazon.com/gp/product/0316328197/?tag=pfamazon01-20" by John Gribbin.

When people forget this, they tend to start treating (somewhat unconsciously) abstract models as something more than a model; as reality. Even though such models are always, by definition, circular ones (like the way we visualize atoms as if they looked like some everyday objects, that are made of atoms).

Such a thinking tends to make it harder to recognize that a wide number of different models can actually also explain all the phenomena we have observed, and thus should not be rejected as an invalid model. Rejecting them goes counter to the scientific paradigm "invented" by Newton. I think he recognized all the scientific ideas we have ever had are just abstract models, as indicated by observations.

That being said, I've never quite understood what exactly is being demonstrated about emitter theory by that Alväger's test. I could be horribly wrong, but I assume it has to do with someone pushing some artificial mental model beyond its limits. And I think the model in question, is the idea that in emitter theory "light moves like bullets", and then it is thought this means that denser matter slows down light as if a bullet was shot into a jelly. I know some people tend to get that idea in their head, because they act so amazed when they are being told that when light enters a medium, it slows down, but when the light exits the air, it speeds up again. Of course, the mental model has just shown its limit.

What emitter theory says, quite simply, is that matter, i.e. atoms, emit light at the speed C relative to themselves. We pretty much know that the speed of light slows down in denser "medium", because every atom inside the medium absorb the light, and with a small delay pass it on. It is these delays that slow down the propagation speed. The more denser the medium, the more atoms to hop through, and the less speed we measure. But the light itself never changes its speed per se. That idea is in agreement with experiment AND Standard Model, as far as I know. If emitter theory was claiming anything different, it would be in trouble.

So my mental model of emitter theory is just like "information packets" being tossed between atoms, hopping from atom to atom. Not light passing through air "like a bullet" from a moving flashlight. Every atom that relays the information, must also regulate its speed.

And that is why I don't understand, how are gamma rays in that experiment suddenly free of the Standard Model? How could a gamma ray pass through some beryllium, mylar window and some 60 meters of air, without ever touching a single atom? Has someone made a meaningful comment about this?

About the binary stars, I thought it was just a commonly accepted fact that the argument is invalid. Because we know now that the vacuum of space is not actually a perfect vacuum, especially nearby binary star systems. We should expect all kinds of stuff to orbit the whole system. In other words, the atoms of all that crap should still be absorbing and re-emitting light, just like in Standard Model.

Also, as far as I know, the original argument was that it would become impossible to see visual binaries because the image would get blurred into one. We know now that only a small portion of binaries are visual binaries, even through a telescope.

http://www.astronomical.org/astbook/binary.html
"Only a small portion of binary stars are visual binaries. In order to see a visual binary, the stars must be separated by fairly wide distances, and the orbital periods are usually very long."

And there are estimates that actually, half of all the stars in the sky are members of binaries;
http://astrosun2.astro.cornell.edu/academics/courses//astro201/binstar.htm
"Five to ten percent of the stars visible to us are visual binary stars. Careful spectroscopic studies of nearby solar-type stars show that about two thirds of them have stellar companions. We estimate that roughly half of all stars in the sky are indeed members of binaries."

--

Hmmm, while I already got a bit philosophical, I would like to carry on with few words about mental models. (sorry :)

Think about the idea of ether. As it became apparent that light was a wave, people applied a mental model of waves on ponds and such, and so thought there must be some sort of matter on which these waves propagate, since waves always propagate as a motion of matter.

Well, we know electromagnetism is what basically makes up matter. Why should anyone expect, that something which makes matter, is also moving "as a motion of matter"? Even if M&M had found that aether exists, it wouldn't mean it is anything like matter in reality.

Or think about an atom. What does an atom look like? Or what does an electron look like? Or quark? What color and what shape are they, or do they look "foggy" or something like that?

How could you ever see what an electron looks like, since it is the very function of the electron to give off a photon. What things look like is wholly dependent on the shape that the sea of photons reveal, but when you tried to see what an electron looks like, all you can do, by definition, is catch a photon it emits. It "looks" like the photon that it gives off. It "looks" like a quantum step of an atom on the measuring instrument.

Or think about quark. It doesn't have such a function as give off a photon. By definition, it doesn't "look" like anything, no matter how close you look. The problem is not that it's "so small". Even if it was two meters wide and three meters high, it still wouldn't "look" like anything, since it doesn't have such a function as to give off a photon at all. (That means it doesn't reflect photons either, since reflection is about absorbing and emitting information)

You can't even "feel" what this quark looks like, since it doesn't have the function that our sense of touch is based on; electromagnetism.

It is difficult to imagine in your mind what is some entity like that by definition does not have any "look". Any shape or color (not even white or black), nor does it collide with your hands like matter. It is difficult, because you classify information by relating things to other things, and in this case there's really nothing else "like" electron, but the electron itself. Or quark. Or photon. (What does a photon look like? Etc...)

But still, people get hung up to all kinds of circular mental models that are out there, as if they were describing any sort of reality. Like you often hear how electron exists on one orbit around an atom, and then it "just disappears from that orbit and re-appears on another orbit, without moving in between". And this is somehow "amazing". Well, it is only amazing to anyone who forgot that the planetary model was just a model. If you are measuring something like frequency, it is not amazing at all to notice that one wave comes in the length X, and the immediate second wave comes in some different length Y.

In fact, when I said "electron gives off a photon", that is also a mental model. We could probably build a perfectly good model where the atom itself gives off a photon (or causes a ripple in space, or whatever floats your boat), thus causing the energy level of itself to drop, which we measure the way we measure it. That electron seems to be like a rainbow or a shadow anyway, caused by the atom, and we just interpetate the measurement as if there was a material particle there (or whatever).

It should also be recognized with all these scientific models, that success breeds success. That means, that when some model is thought to be more elegant than the others due to the experimental data at that point, it tends to shove all the alternative models out of its way, in the sense that they don't get much attention anymore. Had the emitter theory been pushed forwards after M&M test, and become accepted as the "best model" at that time (entirely possible, since the only argument was AFAIK the binary star argument), then advocates of relativity theory would be hit in the head with their "inability to explain inertia", and their "crackpot idea" about relativity of time.

That kind of stuff is always so annoying to me. That's why in my mind no model is ever truly "dead" in the sense that it wouldn't deserve any attention. In my interpetation, the scientific paradigm says we should keep pushing all the models, and inventing new version "just for the heck of it", if we really want to close in on the "truth" :)

So, while I find the mountain of evidence towards relativity very interesting, I think the little problems and the speculation on them is even more interesting :)
I have sympathy for all this kind of stuff:
http://www.wbabin.net/sokolov/sokolov4.pdf

-Anssi

 

[Xeinstein]

Posts 12, 18, 20
If anyone has a good explanation with numbers how a length can Lorentz contract while the Distance between the ends of that length do not Lorentz contract it would certainly falsify my ‘assertion’. So I’d like to see it.

I can only think of one way to do that, by using an “aether”. Which for me disqualifies it as being a “good” explanation, I understand the aether is still acceptable to a few. Ich.

Can somebody explain how a length can Lorentz contract while the Distance between the ends of that length do not Lorentz contract without using an "aether"?

 

[Doc Al]

Can somebody explain how a length can Lorentz contract while the Distance between the ends of that length do not Lorentz contract without using an "aether"?

Can you give an example of what you're talking about?

 

[Xeinstein]

Can you give an example of what you're talking about?

The Bell's co-accelerating ships problem:

-There are two identical spaceships which are initially at rest in "lab-frame".
-These two ships perform IDENTICAL acceleration procedure.
-The ships are launched simultaneously in the lab-frame.

So in the lab-frame, a thin thread connected between the two spaceships will contract and break. But why the distance (in lab-frame) between the two spaceships will not change or contract?

 

[Doc Al]

The Bell's co-accelerating ships problem:

-There are two identical spaceships which are initially at rest in "lab-frame".
-These two ships perform IDENTICAL acceleration procedure.
-The ships are launched simultaneously in the lab-frame.

So in the lab-frame, a thin thread connected between the two spaceships will contract and break. But why the distance (in lab-frame) between the two spaceships will not change or contract?

I like to think of the thread as being stretched and broken. The reason why the distance between the spaceships doesn't change (according to lab frame observers) is because the simultaneous accelerations (simultaneous according to the lab frame) are increasing the distance between the ships in the ship's frame. Once the ships reach their final speed their distance apart (according to them) will be $\gamma L_0$, while it will still be only $L_0$ according to lab frame observers.

See my comments here: https://www.physicsforums.com/showpost.php?p=1561094&postcount=63

 

[1effect]

The Bell's co-accelerating ships problem:

-There are two identical spaceships which are initially at rest in "lab-frame".
-These two ships perform IDENTICAL acceleration procedure.
-The ships are launched simultaneously in the lab-frame.

So in the lab-frame, a thin thread connected between the two spaceships will contract and break. But why the distance (in lab-frame) between the two spaceships will not change or contract?

The exact explanation can be found here

 

[1effect]

I'll describe the problem in my own words.

The co-accelerating ships problem:

-There are two identical spaceships which are initially at rest in "lab-frame".

-These two ships perform IDENTICAL acceleration procedure.

-The ships are launched simultaneously in the lab-frame.

http://www.saunalahti.fi/~anshyy/PhysicsForums/Simultaneity03.jpg"
Red ones are the space ships. Right one is the "front ship". Blue line is an observer who stays at rest, added in there just for convenience. The acceleration events are instantaneous here, but you can imagine any sort of real-world acceleration instead)

Now, since the accelerations are identical in lab-frame, it should hold true that the distance between the ships does NOT change during the acceleration; As measured by the lab-frame, the distance between ships before and after the acceleration is exactly the same.

Obviously in the mechanics of SR, the acceleration procedures are NOT identical from the point of view of the ships. The distance between the ships should stretch in their own POV:

From the "POV" of FRONT SHIP:
Immediately after acceleration, the front ship exists in such an inertial frame that the rear ship must not have been launched yet. If you assert it has, then the front ship will receive information about the launch of the other ship at speeds slower than C

From the "POV" of the REAR SHIP:
Vice versa happens. Immediately after the acceleration, the rear ship exists in such an inertial frame, that the front ship must have been launched much earlier than the rear ship. If you assert it wasn't launched earlier, then the rear ship will receive information about the launch of the front ship at speeds faster than C.

POV is used here to refer to how things "are" in the inertial coordination system of an observer, according to Lorentz-transformation. POV is NEVER used in the meaning of what the observer can SEE; This talk concerns Lorentz-contraction.

In other words, the front ship will accelerate away from the other ship while it is still sitting on the launch pad. Here's what it all looks like from the inertial coordination system that the ships will end up to after acceleration.

http://www.saunalahti.fi/anshyy/PhysicsForums/Simultaneity04.jpg"
Black lines are planes of simultaneity

Even though the ships did go through the same acceleration procedure, after the fact these procedures exist in different moments in time.

We should arrive at the same conclusion even if there is a steel rod between the ships.

And that's not all. Since the ships are performing an identical acceleration, they should stay in the same inertial coordination system at all times. In other words, their notion of simultaneity should be identical at all times. In other words the ships (& the rod) should keep their length from their own perspective, and contract from the perspective of the blue observer.

So it seems that SR very concretely requires that from the POV of the front ship, the rear ship must still be on launch pad after the launch, AND it must be in the same inertial coordination system at all times (i.e. NOT on the launch pad).

There is odd asymmetry in Lorentz-contraction. It occurs to external objects when you switch inertial frames. But at the same time, it doesn't seem to occur if it is the external objects that are switching frames. And if the observer has any volume, he should stretch by the same mechanic that causes contraction (At least if he is being accelerated from the front and from the rear simultaneously).
---

When I first asked about this, it was noted that there is no standard way to construct a coordinate system where non-inertial observer is at rest.

However, if we place the launch pads at far enough distances from each others, and/or use rapid enough acceleration, it is trivial to show that AFTER the acceleration the front ship can exist in such an inertial frame, that the rear ship must not have been launched yet, IF it is true that light approaches the front ship in this new inertial coordination system at speed C.

I was also informed of a FAQ-page regarding this problem. I didn't understand the explanation, if any was even offered:

http://math.ucr.edu/home/baez/physics/Relativity/SR/spaceship_puzzle.html"

They first give instructions to draw similar spacetime diagrams as I have offered above, but with non-instantaneous acceleration. Then they note:



It doesn't make any difference who thinks the accelerations are constant and who doesn't. All that matters is that the acceleration procedures themselves are identical. Surely one acceleration procedure looks the same when performed in any location of the lab-frame.

Then they say:


What does this mean? Just pick the curve to be something else? Just decide that of the two identical accelerations, the other one is not identical?

What is the actual explanation?

You can find it here