[Halc]

There has to be some reality for light though, and we have more and more extreme frames reducing the distance that fast moving matter has to travel through the space dimensions and time dimension with these tending to zero.

I already pointed out that this is wrong.  A fast thing still needs to go through the full distance.  My twin going to some star 10 light years away is going to need at least 10 years to get there at any speed.  That his clock doesn't log that doesn't make the distance shorter.
If you look at it in his frame, he's not going anywhere, so it just takes say 1 year for the star to travel the one light year to him, and those events (star location at start and end) were always that close in that frame.

The only frame that actually reduce or otherwise alter lengths are accelerating frames.

[mad aetherist (OP)]

I must admit that i dont understand. But ok what about this -- X & Y are going along at speed to the left together with a new tight thread tween -- & then X & Y decelerate at the same time & rate etc -- what happens now?

'At the same time' in which frame?  The answer very much depends on this.

Assuming you mean simultaneously in your observer O's frame in which X and Y are going along at speed, then the string will go slack.

Ok, then what about in X's frame & in Y's frame?

[Halc]

Ok, then what about in X's frame & in Y's frame?[/quote]
That's your original scenario A.  The ships start accelerating in the frame in which they're initially at rest.  The string breaks.

[mad aetherist (OP)]

I must admit that i dont understand. But ok what about this -- X & Y are going along at speed to the left together with a new tight thread tween -- & then X & Y decelerate at the same time & rate etc -- what happens now?

'At the same time' in which frame?  The answer very much depends on this.
Assuming you mean simultaneously in your observer O's frame in which X and Y are going along at speed, then the string will go slack.

Ok, then what about in X's frame & in Y's frame?

Ok, then what about in X's frame & in Y's frame?

That's your original scenario A.  The ships start accelerating in the frame in which they're initially at rest.  The string breaks.

No its scenario B2, X & Y are going along & then decelerate. There are 3 questions in B2, they can be called B2X B2Y & B2O, ie what do observers X & Y & O see, & u in effect answered B2O (what does O see)(O is stationary) & my question was in effect B2X & B2Y (what do X & Y see).

[David Cooper]

There has to be some reality for light though, and we have more and more extreme frames reducing the distance that fast moving matter has to travel through the space dimensions and time dimension with these tending to zero.

I already pointed out that this is wrong.

It isn't wrong - in the 4D geometry you can always consider a moving object to be stationary, thereby allowing it to make a journey from one point in Spacetime to another just by sitting still in the space dimensions and moving through the time dimension - such a path always exists for any object, and the smaller the number of ticks its clock makes between those two points, the shorter the length of that path will be through time. For an object moving a tiny fraction more slowly than light, it will reduce the distance of what appears to be a long trip to other observers to zero length and almost zero time. Light will reduce any similar trip to zero distance and zero time.

A fast thing still needs to go through the full distance.

The distance is always zero in the space dimensions of 4D Spacetime for any travelling object - not just light. It is only the time dimension that the lengths vary for different objects.

My twin going to some star 10 light years away is going to need at least 10 years to get there at any speed.  That his clock doesn't log that doesn't make the distance shorter.

He says that he isn't travelling any distance at all, but that you are, but he's wrong too. In 4D Spacetime, you are both travelling zero distance through space for your "trips".

If you look at it in his frame, he's not going anywhere, so it just takes say 1 year for the star to travel the one light year to him, and those events (star location at start and end) were always that close in that frame.

The only frame that actually reduce or otherwise alter lengths are accelerating frames.

The important point is that these zero-length paths are always available to matter (except that they aren't zero through the time dimension, but they can get close to zero for that too), and they must also be available to light too (with the length through the time dimension actually reaching zero). And if that sounds bonkers, don't blame me. It's because SR is bonkers.

[Halc]

Ok, then what about in X's frame

Ok, then what about in X's frame & in Y's frame?

That's your original scenario A.  The ships start accelerating in the frame in which they're initially at rest.  The string breaks.

No its scenario B2, X & Y are going along & then decelerate.

You asked to do it in X and Y's frame.  In that frame, X and Y are stationary, not decelerating.  In that frame, X and Y start stationary, and accelerate to some speed, which is scenario A.

Anyway, I think I see what you mean.  Describe the situation from frame O, but X and Y start 'declerating' simultaneously as defined in their own frame, not in O's frame.  Then yes the string breaks because in O's frame, Y starts slowing down first, immediately breaking the string.

[mad aetherist (OP)]

Ok, then what about in X's frame

Ok, then what about in X's frame & in Y's frame?

That's your original scenario A.  The ships start accelerating in the frame in which they're initially at rest.  The string breaks.

No its scenario B2, X & Y are going along & then decelerate.

You asked to do it in X and Y's frame.  In that frame, X and Y are stationary, not decelerating.  In that frame, X and Y start stationary, and accelerate to some speed, which is scenario A.

Anyway, I think I see what you mean.  Describe the situation from frame O, but X and Y start 'declerating' simultaneously as defined in their own frame, not in O's frame.  Then yes the string breaks because in O's frame, Y starts slowing down first, immediately breaking the string.

So, in every scenario ship X & ship Y apart from any obvious mechanical strains must suffer a relativistic strain along their full lengths (but praps moreso near midlength) which is stretching or compressing ship X (& similarly ship Y), & this strain must result in a relativistic force-stress.
Or, there is a relativistic strain but not a realworld strain hencely no associated realworld force-stress (force).
And i suspect that that strain & force-stress depends on whether u are observing from XY or from O.

[Halc]

So, in every scenario ship X & ship Y apart from any obvious mechanical strains must suffer a relativistic strain along their full lengths (but praps moreso near midlength) which is stretching or compressing ship X (& similarly ship Y), & this strain must result in a relativistic force-stress.

A typical rocket is one piece and has all the thrust coming from the rear, which is going to naturally put compressive stress on the thing, and the relativistic shortening I suppose will relieve that a tiny bit.
A railroad train on the other hand is pulled from the front, and if it is long enough, no amount of strength will prevent the train from breaking due to the additional tension relativity adds.  The limit to the length of the train, as a function of the acceleration of the engine, is called the Rindler Horizon, which is the acceleration equivalent of the event horizon of a black hole.  So when you accelerate with your car from a stop sign, you define such a Rindler Horizon somewhere behind you where an object would need to move at light speed in order to stay stationary with you in your frame.  The harder you accelerate, the closer that horizon is.

Or, there is a relativistic strain but not a realworld strain hencely no associated realworld force-stress (force).

It's quite real.  The string really breaks due to actual stress.

And i suspect that that strain & force-stress depends on whether u are observing from XY or from O.

It has nothing to do with being observed or not, or by whom.

[David Cooper]

So, in every scenario ship X & ship Y apart from any obvious mechanical strains must suffer a relativistic strain along their full lengths (but praps moreso near midlength) which is stretching or compressing ship X (& similarly ship Y), & this strain must result in a relativistic force-stress.
Or, there is a relativistic strain but not a realworld strain hencely no associated realworld force-stress (force).
And i suspect that that strain & force-stress depends on whether u are observing from XY or from O.

We can't tell if a ship is accelerating or decelerating, so it may be contracting in length or extending (uncontracting). If we could measure the difference, we would break relativity and identify the absolute frame. Any delay in contracting or extending should produce a stretching or compression force. This will be a smaller effect than the compression or stretching of the object caused by the force being applied to change its speed, but we can ignore any such compression or stretching from the push or pull because it will be the same for both cases - the effect we're looking for will be much smaller, but it will either be a compression or a stretch. I suspect it will be cancelled out in some way though so that it can't be measured, and it's easy to see straight away that any ruler-like tool you use to measure the effect will be affected equally, so it will mis-read and hide the effect. But what about a light clock with mirrors at opposite ends of a space ship? Well, again, if you compare that with a smaller light clock, both will be compressed or stretched in the same way and the effect we're looking for will be masked.

Any attempt to measure the ship's length by an observer who isn't accelerating will always measure the ship as contracting if he thinks it's accelerating and extending if he thinks it's decelerating, so again the effect we're looking for is hidden.

What if we could just watch two atoms though and measure the distance between them visually? The atoms themselves should contract or extend, and the spacing between them needs to adjust accordingly, so if it's a deceleration, they should keep finding themselves too close together and push apart a bit more often than the opposite. The trouble with that is that they're already going to be moving around a lot and the effect we want to see is infinitesimal by comparison, but the question is whether it is in principle detectable or not. Also, if the acceleration is severe, the compression or stretch won't be so terribly small. What happens to a camera that's looking in from the side? The film/CCD isn't a single point, so it will be suffering from the same compression or stretch and the effect we're looking for will be masked. The shape of the atoms will also be stretched or compressed to the same extent, so any stretch or compression of the space between them will be matched by distortions of their own shape, and with the same distortions applying to the camera, there's no way to reveal the reality as to whether there's compression or stretch. It's a hopeless task - the phenomenon of relativity wins every time, hiding the truth from us.

[David Cooper]

I've come up with an idea for an experiment.

Imagine a rocket with a lot of mass aligned perpendicular to its direction of travel (to avoid it having any length). Sticking out ahead of it though, and behind, are four rods: two pointing ahead and two behind. On the ends of one of each pair of rods is a large mass, while the rods themselves weigh very little. The idea here is that when we accelerate/decelerate the rods, any stretch or compression caused by length contraction/extension will take different amounts of time to adjust the length of a rod with a large mass on the end of it compared with the rod next to it with no such mass at the end.

We're looking for a difference in length between the two rods of each pair, but we'll only get that during an acceleration/deceleration, and while there's a force applying, there will already be compression or stretch in play in the rods due to the acceleration itself (while any length contraction adjustment is a much smaller effect). The rods ahead of the ship will be compressed and the ones behind will be stretched. If we always apply the same rate of acceleration, the difference between the two rods in a pair will always be the same - the ones with the large mass at their end will be worse affected than their partner, the leading one being more compressed and the trailing one being more extended. We can make a mark on the rod that's longer than its partner during acceleration to show how far along it its partner reaches. Any effect from length-contraction adjustments should show up as variations in length of the shorter rod (only shorter during acceleration) away from that mark.

It may be worth naming the rods, so F means forward-pointing while R means rearward. H means heavy and L means light (though we're really talking about mass). We thus have four rods called: FH, FL, RH and RL. The compression under acceleration will make FH shorter than FL, and stretch will make RH longer than RL, so we can put marks on FL and RH to show how far the other rods will reach along them, and these marks can be called MF and MR.

At the moment when the ship makes a transition from deceleration to acceleration, there should be no extra compression or stretch from length contraction, so the ends of the shorter rods should exactly meet their mark. Here's the important point: this means that any variation at other times should allow us to identify the absolute frame (unless I've missed some important factor).

Case 1:-

If the rocket is accelerating and there is a change in the amount of length contraction needed for the current speed, that means a contraction has to be applied through the rods becoming slightly more stretched (RH and RL) or less compressed (FH and FL), and the ones with and without large masses at the end of them should take different lengths of time to adjust. The mass of the ship is much greater than the large masses at the ends of the rods, but because we also have rods pointing both ways, they have to change length without the ship end of any rods accelerating at a different rate from the ship - it's the ends with the masses on the end of them that must migrate.

Rod RH (already stretched by the acceleration) has a bit of extra effective stretch added to it by length contraction, as does RL, and it should take longer to adjust for this contraction than RL because rod RL has more work to do to haul the large mass in, so the end of RL should move away from mark MR, and it should do so in a direction taking it even further away from the end of RH.

[Rods FH and FL are more complex, so I'll leave them till later.]

Case 2:-

If the rocket is decelerating, the rods will have to extend rather than contracting, so the rods should become slightly more compressed (RH and RL) or less stretched (FH and FL), and the ones with and without large masses at the end should again take different lengths of time to adjust.

Rods FH and FL are easier to handle in case 2 because they will behave in a similar way to FH and FL did in case 1, the difference being that we're adding compressions rather than stretches. They are compressed by the acceleration and now have a bit of effective compression added by the length extension, so FH will take longer to respond and its end will fall short of mark MF on FL.

Rod RH (already stretched by the acceleration) should have a bit of effective compression added to it by length extension (or decontraction), as does RL, removing some of the stretch and allowing the rod to lengthen, but I'm not sure how it would react. Is it a hindrance as before, or is it now going to help extend the rod more quickly? If the latter, then it could hide the effect we're trying to see, but remember that it should still show up when the ship is momentarily stationary (moving from deceleration to acceleration), because at that point the ends of the shorter rods would line up with the marks. Either way then, we should have a method by which the absolute frame could be identified, unless there's a fault somewhere in the argument (which I fully expect to be the case, but if it turns out that there isn't, it would be a shame to miss the experiment that finds the aether by assuming that no such experiment can exist). This looks viable, but I've been here before several times with ideas for experiments that looked as if they could break relativity, and I haven't put a lot of time into attacking this one yet, so don't get excited. I've just posted it up front on the off chance that it might stand up, and if it does, the time and date stamp on it could be handy.

Demolitions invited.

[mad aetherist (OP)]

I've come up with an idea for an experiment.

Imagine a rocket with a lot of mass aligned perpendicular to its direction of travel (to avoid it having any length). Sticking out ahead of it though, and behind, are four rods: two pointing ahead and two behind. On the ends of one of each pair of rods is a large mass, while the rods themselves weigh very little. The idea here is that when we accelerate/decelerate the rods, any stretch or compression caused by length contraction/extension will take different amounts of time to adjust the length of a rod with a large mass on the end of it compared with the rod next to it with no such mass at the end.

We're looking for a difference in length between the two rods of each pair, but we'll only get that during an acceleration/deceleration, and while there's a force applying, there will already be compression or stretch in play in the rods due to the acceleration itself (while any length contraction adjustment is a much smaller effect). The rods ahead of the ship will be compressed and the ones behind will be stretched. If we always apply the same rate of acceleration, the difference between the two rods in a pair will always be the same - the ones with the large mass at their end will be worse affected than their partner, the leading one being more compressed and the trailing one being more extended. We can make a mark on the rod that's longer than its partner during acceleration to show how far along it its partner reaches. Any effect from length-contraction adjustments should show up as variations in length of the shorter rod (only shorter during acceleration) away from that mark.

It may be worth naming the rods, so F means forward-pointing while R means rearward. H means heavy and L means light (though we're really talking about mass). We thus have four rods called: FH, FL, RH and RL. The compression under acceleration will make FH shorter than FL, and stretch will make RH longer than RL, so we can put marks on FL and RH to show how far the other rods will reach along them, and these marks can be called MF and MR.

At the moment when the ship makes a transition from deceleration to acceleration, there should be no extra compression or stretch from length contraction, so the ends of the shorter rods should exactly meet their mark. Here's the important point: this means that any variation at other times should allow us to identify the absolute frame (unless I've missed some important factor).

Case 1:-

If the rocket is accelerating and there is a change in the amount of length contraction needed for the current speed, that means a contraction has to be applied through the rods becoming slightly more stretched (RH and RL) or less compressed (FH and FL), and the ones with and without large masses at the end of them should take different lengths of time to adjust. The mass of the ship is much greater than the large masses at the ends of the rods, but because we also have rods pointing both ways, they have to change length without the ship end of any rods accelerating at a different rate from the ship - it's the ends with the masses on the end of them that must migrate.

Rod RH (already stretched by the acceleration) has a bit of extra effective stretch added to it by length contraction, as does RL, and it should take longer to adjust for this contraction than RL because rod RL has more work to do to haul the large mass in, so the end of RL should move away from mark MR, and it should do so in a direction taking it even further away from the end of RH.

[Rods FH and FL are more complex, so I'll leave them till later.]

Case 2:-

If the rocket is decelerating, the rods will have to extend rather than contracting, so the rods should become slightly more compressed (RH and RL) or less stretched (FH and FL), and the ones with and without large masses at the end should again take different lengths of time to adjust.

Rods FH and FL are easier to handle in case 2 because they will behave in a similar way to FH and FL did in case 1, the difference being that we're adding compressions rather than stretches. They are compressed by the acceleration and now have a bit of effective compression added by the length extension, so FH will take longer to respond and its end will fall short of mark MF on FL.

Rod RH (already stretched by the acceleration) should have a bit of effective compression added to it by length extension (or decontraction), as does RL, removing some of the stretch and allowing the rod to lengthen, but I'm not sure how it would react. Is it a hindrance as before, or is it now going to help extend the rod more quickly? If the latter, then it could hide the effect we're trying to see, but remember that it should still show up when the ship is momentarily stationary (moving from deceleration to acceleration), because at that point the ends of the shorter rods would line up with the marks. Either way then, we should have a method by which the absolute frame could be identified, unless there's a fault somewhere in the argument (which I fully expect to be the case, but if it turns out that there isn't, it would be a shame to miss the experiment that finds the aether by assuming that no such experiment can exist). This looks viable, but I've been here before several times with ideas for experiments that looked as if they could break relativity, and I haven't put a lot of time into attacking this one yet, so don't get excited. I've just posted it up front on the off chance that it might stand up, and if it does, the time and date stamp on it could be handy.
Demolitions invited.

Are the rods connected to the ship?
Is it an Einsteinian universe?  Or an aether universe?
In an aether universe any object would contract-stretch on each side of its center of mass. An observer moving with the object would not see any change in shape, but might notice any slight movement of the center of mass. That movement would be made up of a real movement, plus a faux-movement -- the faux being due to the movement of the observer's eyes in relation to the observer's own center of mass.

In an Einstein universe there is no real contraction or stretching. And no apparent contraction or stretching, any such contraction or stretching being a math-trick model. Or, if u like, the contraction or stretching are apparent, but are due to a change in the measuring rod & measuring clock.

[David Cooper]

Are the rods connected to the ship?

The description says so.

Is it an Einsteinian universe?  Or an aether universe?

I'm working to LET - makes most sense to work with a rational theory where you don't get tied up in unnecessary complexities that make it hard to see what you're doing. Point is though, this is a test that could be made in the real universe which would, if there's no fault in the idea, pin down the absolute frame. If that happened, LET would survive, but some disproven theories would be disproved through direct experimental observations without needing to apply any of that weird reasoning witchcraft from the mathematicians that physicists don't like.

In an aether universe any object would contract-stretch on each side of its center of mass.

Exactly - the rods will contract or uncontract, pulling in towards the centre where all the mass of the space ship is sitting (distributed sideways so that we can avoid worrying about its contraction interfering).

An observer moving with the object would not see any change in shape, but might notice any slight movement of the center of mass. That movement would be made up of a real movement, plus a faux-movement -- the faux being due to the movement of the observer's eyes in relation to the observer's own center of mass.

The only thing we need to observe is the location of the ends of the shorter rods relative to the marks on the longer ones (while the rods are only of different lengths while accelerating - when at rest, they're all the same length).

In an Einstein universe there is no real contraction or stretching. And no apparent contraction or stretching, any such contraction or stretching being a math-trick model. Or, if u like, the contraction or stretching are apparent, but are due to a change in the measuring rod & measuring clock.

I'm not bothered about what SR or GR have to say on the matter - if this experiment identifies the absolute frame, it doesn't matter what they have to say on the matter as the symmetry will have been broken. That said though, if it's too hard to carry out the experiment due to the infinitesimal size of the effect we're looking for, it would still provide an interesting distinction between LET and SR/GR which the latter cannot possibly match. The big question though is, does LET actually predict this or have I made a mistake somewhere with the experiment and my predicted results?

[Halc]

I've come up with an idea for an experiment.

Imagine a rocket with a lot of mass aligned perpendicular to its direction of travel (to avoid it having any length). Sticking out ahead of it though, and behind, are four rods: two pointing ahead and two behind. On the ends of one of each pair of rods is a large mass, while the rods themselves weigh very little. The idea here is that when we accelerate/decelerate the rods, any stretch or compression caused by length contraction/extension will take different amounts of time to adjust the length of a rod with a large mass on the end of it compared with the rod next to it with no such mass at the end.

We're looking for a difference in length between the two rods of each pair, but we'll only get that during an acceleration/deceleration, and while there's a force applying, there will already be compression or stretch in play in the rods due to the acceleration itself (while any length contraction adjustment is a much smaller effect). The rods ahead of the ship will be compressed and the ones behind will be stretched. If we always apply the same rate of acceleration, the difference between the two rods in a pair will always be the same - the ones with the large mass at their end will be worse affected than their partner, the leading one being more compressed and the trailing one being more extended. We can make a mark on the rod that's longer than its partner during acceleration to show how far along it its partner reaches. Any effect from length-contraction adjustments should show up as variations in length of the shorter rod (only shorter during acceleration) away from that mark.

It may be worth naming the rods, so F means forward-pointing while R means rearward. H means heavy and L means light (though we're really talking about mass). We thus have four rods called: FH, FL, RH and RL. The compression under acceleration will make FH shorter than FL, and stretch will make RH longer than RL, so we can put marks on FL and RH to show how far the other rods will reach along them, and these marks can be called MF and MR.

At the moment when the ship makes a transition from deceleration to acceleration, there should be no extra compression or stretch from length contraction, so the ends of the shorter rods should exactly meet their mark.

I followed all that.

Here's the important point: this means that any variation at other times should allow us to identify the absolute frame (unless I've missed some important factor).

What???  It allows us to identify the direction of acceleration.  Acceleration is absolute (sort of), so you’ve found a complicated way to measure that.  A simple plumb line would also work.

Still reading, but not sure what you expect here.

Case 1:-

If the rocket is accelerating and there is a change in the amount of length contraction needed for the current speed, that means a contraction has to be applied through the rods becoming slightly more stretched (RH and RL) or less compressed (FH and FL), and the ones with and without large masses at the end of them should take different lengths of time to adjust. The mass of the ship is much greater than the large masses at the ends of the rods, but because we also have rods pointing both ways, they have to change length without the ship end of any rods accelerating at a different rate from the ship - it's the ends with the masses on the end of them that must migrate.

You’re saying that you’re making a change to the acceleration rate and it effects the strain on all 4 of the rods, taking some finite time to find a new equilibrium.
Not sure where relativistic contraction is involved.  Perhaps you need to identify the frame in which these measurements are going to be taken, because I don’t think you mean the frame of the ship.  Maybe you do.  Hard to tell.  There’s no relativistic contraction in ship frame, just static strain, or dynamic strain if the acceleration is not constant.

Rod RH (already stretched by the acceleration) has a bit of extra effective stretch added to it by length contraction,

How does contraction add to stretch?  Wouldn’t they potentially cancel if they happen to be equal?  Sorry to interrupt mid-sentence...

as does RL, and it should take longer to adjust for this contraction than RL because rod RL has more work to do to haul the large mass in, so the end of RL should move away from mark MR, and it should do so in a direction taking it even further away from the end of RH.

If you increase your acceleration, then yes.  Constant proper acceleration, going ever slower or faster in some other inertial frame, will not align RL with a different place on RH.

Case 2:-

If the rocket is decelerating,

OK, definitely a different frame.  I know which one now.

the rods will have to extend rather than contracting, so the rods should become slightly more compressed (RH and RL) or less stretched (FH and FL), and the ones with and without large masses at the end should again take different lengths of time to adjust.

OK, I think this makes a little sense if RH and RL are in the direction of acceleration, compressed strain.  You sort of have the ship backwards from the way I envision it.
For one, if something is moving, it is relativistically contracted, and as it slows in your frame, it will become less contracted, but never actually extended (longer than its proper length).  The rods RH and RL are compressed by strain, and the one endpoint stays at the mark on the partner rod.

Rods FH and FL are easier to handle in case 2 because they will behave in a similar way to FH and FL did in case 1, the difference being that we're adding compressions rather than stretches. They are compressed by the acceleration and now have a bit of effective compression added by the length extension, so FH will take longer to respond and its end will fall short of mark MF on FL.

Sorry,  I just cannot parse this.  “effective compression added by the length extension” seems self contradictory.  I don’t know what you’re trying to convey with those words.  Extension does not add to compression, it would seem to relieve it.

Rod RH (already stretched by the acceleration)

I thought we were decellerating.  You need to clarify which way the ship faces, and which way thrust is being applied.  It seems to switch from sentence to sentence, so I have a very hard time critiquing the experiment.

I got lost after that.  I will look again with some clarifications.  Not saying anything is wrong, just lacking clarity so far.

[David Cooper]

At the moment when the ship makes a transition from deceleration to acceleration, there should be no extra compression or stretch from length contraction, so the ends of the shorter rods should exactly meet their mark. Here's the important point: this means that any variation at other times should allow us to identify the absolute frame (unless I've missed some important factor).

There may be an error there if the speed of the rods isn't the same all the way along them due to changes in length as middle hits zero speed, and that will doubtless destroy the ability of the experiment to identify the absolute frame if case 1 and case 2 produce the same changes away from the marks (in the same direction rather than in opposite directions), so it's the last part of case 2 that needs to be resolved. Does the mass hinder or help the rod lengthen?

A reminder of that part:-

Rod RH (already stretched by the acceleration) should have a bit of effective compression added to it by length extension (or decontraction), as does RL, removing some of the stretch and allowing the rod to lengthen, but I'm not sure how it would react. Is it a hindrance as before, or is it now going to help extend the rod more quickly?

[mad aetherist (OP)]

Are the rods connected to the ship?

The description says so.

Is it an Einsteinian universe?  Or an aether universe?

I'm working to LET - makes most sense to work with a rational theory where you don't get tied up in unnecessary complexities that make it hard to see what you're doing. Point is though, this is a test that could be made in the real universe which would, if there's no fault in the idea, pin down the absolute frame. If that happened, LET would survive, but some disproven theories would be disproved through direct experimental observations without needing to apply any of that weird reasoning witchcraft from the mathematicians that physicists don't like.

In an aether universe any object would contract-stretch on each side of its center of mass.

Exactly - the rods will contract or uncontract, pulling in towards the centre where all the mass of the space ship is sitting (distributed sideways so that we can avoid worrying about its contraction interfering).

An observer moving with the object would not see any change in shape, but might notice any slight movement of the center of mass. That movement would be made up of a real movement, plus a faux-movement -- the faux being due to the movement of the observer's eyes in relation to the observer's own center of mass.

The only thing we need to observe is the location of the ends of the shorter rods relative to the marks on the longer ones (while the rods are only of different lengths while accelerating - when at rest, they're all the same length).

In an Einstein universe there is no real contraction or stretching. And no apparent contraction or stretching, any such contraction or stretching being a math-trick model. Or, if u like, the contraction or stretching are apparent, but are due to a change in the measuring rod & measuring clock.

I'm not bothered about what SR or GR have to say on the matter - if this experiment identifies the absolute frame, it doesn't matter what they have to say on the matter as the symmetry will have been broken. That said though, if it's too hard to carry out the experiment due to the infinitesimal size of the effect we're looking for, it would still provide an interesting distinction between LET and SR/GR which the latter cannot possibly match. The big question though is, does LET actually predict this or have I made a mistake somewhere with the experiment and my predicted results?

U mention an absolute frame but u dont mention whether u expect an allowance for LC in accordance with relativity (gamma).

[David Cooper]

Here's the important point: this means that any variation at other times should allow us to identify the absolute frame (unless I've missed some important factor).

What???  It allows us to identify the direction of acceleration.  Acceleration is absolute (sort of), so you’ve found a complicated way to measure that.  A simple plumb line would also work.

In an LET universe, when an object accelerates, it contracts in length regardless of whether it's being pulled or pushed up to speeds. If you take an elastic band and accelerate every atom of it up to 0.86c simultaneously in an instant, it will find itself to be stretched to twice its unstressed length, so it will shorten. The question is whether that stress could be detected in any way during an acceleration, and if it can, it would be different for a deceleration from 0.86c to zero, because that would lengthen it instead and lead to it going loose (or to a solid rod being compressed after the deceleration and needing to extend).

You’re saying that you’re making a change to the acceleration rate and it effects the strain on all 4 of the rods, taking some finite time to find a new equilibrium.

The acceleration of the ship as a whole is constant, but the ends will either contract in or extend out, and I'm looking to see if that can be detected and if the two different things can be told apart.

Not sure where relativistic contraction is involved.  Perhaps you need to identify the frame in which these measurements are going to be taken, because I don’t think you mean the frame of the ship.  Maybe you do.  Hard to tell.  There’s no relativistic contraction in ship frame, just static strain, or dynamic strain if the acceleration is not constant.

The measurements are made in the ship's frame of reference, but LET says that it is either contracting or extending (= uncontracting). Throw off your SR glasses for this and try to see it through LET. You may be the only other person here capable of thinking through this stuff properly, so I'd certainly value your help.

Rod RH (already stretched by the acceleration) has a bit of extra effective stretch added to it by length contraction,

How does contraction add to stretch?  Wouldn’t they potentially cancel if they happen to be equal?  Sorry to interrupt mid-sentence...

If you have an piece of rubber a lightyear long which is capable of being stretched to twice its normal length without breaking, accelerating every part of it to 0.866c in a second would leave it in a stretched state due to length contraction. It will then take a good few years to contract, although it might break up in the attempt.

as does RL, and it should take longer to adjust for this contraction than RL because rod RL has more work to do to haul the large mass in, so the end of RL should move away from mark MR, and it should do so in a direction taking it even further away from the end of RH.

If you increase your acceleration, then yes.  Constant proper acceleration, going ever slower or faster in some other inertial frame, will not align RL with a different place on RH.

The length contraction should accelerate the end of the rear rods more than the ship as a whole, and that's the effect we want to detect. If RL contracts more quickly than RH because of the large mass on the end of RH, they should contract at different rates and show up the length contraction that can't normally be detected, making it visible to observers in all frames.

the rods will have to extend rather than contracting, so the rods should become slightly more compressed (RH and RL) or less stretched (FH and FL), and the ones with and without large masses at the end should again take different lengths of time to adjust.

OK, I think this makes a little sense if RH and RL are in the direction of acceleration, compressed strain.  You sort of have the ship backwards from the way I envision it.

Rods RH and RL are pointing rearward from the ship, while FH and FL point forwards. The people on the ship imagine that they're accelerating (in the forward direction) in both cases, but if they were moving to begin with, they may actually be decelerating. Case 1 and case 2 seem identical to the people in the ship, unless they see different behaviour in the rods regarding whether the ends of the shorter ones are level with the marks on the longer ones. In both cases, rods RH and RL are being stretched as they're being pulled along, whereas FH and FL are being pushed by the ship and are being compressed.

For one, if something is moving, it is relativistically contracted, and as it slows in your frame, it will become less contracted, but never actually extended (longer than its proper length).

Indeed, which is why I also call the extension decontraction - it is an undoing of a contraction as the ship decelerates, slowing down relative to the absolute frame that the experiment is designed to try to identify.

The rods RH and RL are compressed by strain, and the one endpoint stays at the mark on the partner rod.

It's FH and FL that are compressed by the acceleration of the ship as they're the ones pointing forwards. Remember that the F and R in the names stand for forward and rearward while the other letters refer to whether they're heavy or light (meaning that they either have a large mass attached to their far end or they have nothing there at all.)

Rods FH and FL are easier to handle in case 2 because they will behave in a similar way to FH and FL did in case 1, the difference being that we're adding compressions rather than stretches. They are compressed by the acceleration and now have a bit of effective compression added by the length extension, so FH will take longer to respond and its end will fall short of mark MF on FL.

Sorry,  I just cannot parse this.  “effective compression added by the length extension” seems self contradictory.  I don’t know what you’re trying to convey with those words.  Extension does not add to compression, it would seem to relieve it.

If we slow something from 0.86c to zero in an instant, it will be compressed, and it will immediately extend as a result. When we decelerate, we get extension (loss of contraction), and that extension is driven by forces pushing the particles further apart to remove compression. FH and FL are compressed by the acceleration, but if it's actually a deceleration, there's extension to add to this, and that means they feel more compressed and push harder. FL reacts more quickly than FH because it doesn't have a great mass at the end to push forward.

Rod RH (already stretched by the acceleration)

I thought we were decellerating.  You need to clarify which way the ship faces, and which way thrust is being applied.  It seems to switch from sentence to sentence, so I have a very hard time critiquing the experiment.

All the information needed was there, but it takes effort and time to take in what's going on in experiments of this kind, so it's easy to miss crucial details. RH faces rearward and is being pulled along, so it is stretched by that. The part that I'm having difficulty with though is working out what happens when a compression (from length extension [undoing a contraction]) is added to that stretched rod and its partner RL. What will happen to the end of RL and the mark on RH? If it moves the same way in case 2 as it does in case 1, then relativity survives as the absolute frame is not identified (as there would doubtless be something that hides the effect at zero speed too, as I mentioned in my previous post).

[David Cooper]

U mention an absolute frame but u dont mention whether u expect an allowance for LC in accordance with relativity (gamma).

I don't know what you're getting at. We're trying to measure the length contraction or the removal of contraction and using Lorentz Ether Theory as our guide. If the ship is accelerating, the rods will contract. If it's decelerating, they'll lengthen instead as the contraction is gradually removed. What I've tried to do is design an experiment where this change in length is slower for some rods than for others so that the difference will show up, but it won't show up if the visual result is the same for acceleration and deceleration. I was expecting to show that the effect was the same for both, but I haven't managed to prove to myself yet that it will be. If the ship slows to zero and then accelerates again, for a moment there will be no contraction or extension applying and it looks as if that might show up a difference unless it's hidden by the fact that not all parts of any of the rods are quite moving at the same speed as each other. I expect that will mask the effect and the experiment will be incapable of detecting the absolute frame, but the easiest place to push for an answer is probably to work out what will happen to the rearward-pointing rods in case 2 (of the forward-pointing ones in case 1). I'm just struggling to find the answer for that at the moment and probably need to think about it for a day or so to find the right way to handle it.

[mad aetherist (OP)]

U mention an absolute frame but u dont mention whether u expect an allowance for LC in accordance with relativity (gamma).

I don't know what you're getting at. We're trying to measure the length contraction or the removal of contraction and using Lorentz Ether Theory as our guide. If the ship is accelerating, the rods will contract. If it's decelerating, they'll lengthen instead as the contraction is gradually removed. What I've tried to do is design an experiment where this change in length is slower for some rods than for others so that the difference will show up, but it won't show up if the visual result is the same for acceleration and deceleration. I was expecting to show that the effect was the same for both, but I haven't managed to prove to myself yet that it will be. If the ship slows to zero and then accelerates again, for a moment there will be no contraction or extension applying and it looks as if that might show up a difference unless it's hidden by the fact that not all parts of any of the rods are quite moving at the same speed as each other. I expect that will mask the effect and the experiment will be incapable of detecting the absolute frame, but the easiest place to push for an answer is probably to work out what will happen to the rearward-pointing rods in case 2 (of the forward-pointing ones in case 1). I'm just struggling to find the answer for that at the moment and probably need to think about it for a day or so to find the right way to handle it.

Ok so gamma is needed for LC. And here gamma only applys to absolute speed, ie not to acceleration.

And we dont have to include some sort of silly Einsteinian LC related to gravitational potential (ie based on equivalence of GP to inertial acceleration). I believe in gravitational potential affecting LC due to nearness to mass (but not for GR reasons), but i dont believe in this LC being present when inertial acceleration is acting (unlike GR).

[Halc]

In an LET universe, when an object accelerates, it contracts in length regardless of whether it's being pulled or pushed up to speeds. If you take an elastic band and accelerate every atom of it up to 0.86c simultaneously in an instant, it will find itself to be stretched to twice its unstressed length, so it will shorten. The question is whether that stress could be detected in any way during an acceleration, and if it can, it would be different for a deceleration from 0.86c to zero, because that would lengthen it instead and lead to it going loose (or to a solid rod being compressed after the deceleration and needing to extend).

I will respond to the whole post in time, but I must point out that the two universes predict the same things in every way.  So if I decelerate an unstressed rubber band instantly, it will find itself too short and need to spring back to its full dimensions just like you describe.  This works in LET as well as Einstein’s view.  If you find the two different, you’ve probably got a mistake somewhere.  This one was pretty easy to spot.

So I agree with your description there, but you make it sound like SR would predict otherwise.

[Halc]

(ie based on equivalence of GP to inertial acceleration)

Assuming GP is gravitational potential, those two are not equivalent.  Acceleration is equivalent to gravitational force, not gravitational potential.  Dilation is a function of GP, which makes it equivalent to speed (not acceleration) in that regard.