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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).
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.
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.
Quote from: HalcQuoteRod 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 a 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.
QuoteRod 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...
Rod RH (already stretched by the acceleration) has a bit of extra effective stretch added to it by length contraction,
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.
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.
If we slow something from 0.86c to zero in an instant, it will be compressed, and it will immediately extend as a result.
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) 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).
From the point of view of the people in the ship, it's always moving in the same direction,
For the rearward-pointing rods, extension should reduce the amount of acceleration acting on them, while contraction should increase it.
If you increase the acceleration force, the rod with the large mass on the end will lengthen more than its partner, whereas if you decrease the force, it will shorten more than its partner, which means the end of the rod without the mass on its end will move relative to the mark.
The solution to this though is to recognise that while the force changes due to length contraction/extension
I got there by replacing the rods with elastic to multiply the differences and make things easier to see clearly. If you imagine one piece of elastic with a weight on the end of it and the other without, the one with the weight may stretch out to twice the length under acceleration while the other one hardly stretches at all.
Quote from: David Cooper on 24/10/2018 18:43:29From the point of view of the people in the ship, it's always moving in the same direction,It is always thrusting in the same direction. They can’t detect motion at all, and for all they know (without a window), they’re sitting in a building on a planet. They detect a force, and that’s it. The rods and stuff would all behave the same from their POV if it were uniform gravity and no speed whatsoever.
QuoteFor the rearward-pointing rods, extension should reduce the amount of acceleration acting on them, while contraction should increase it.This is incorrect. Both increase the acceleration.
In both cases, the R rods experience more g force than the main ship (and the F rods less g force). In the decelerating case, it is because the far ends of the R rods are already moving faster than the ship, but are slowing more than is the ship, to eventually match the ship’s speed when it reaches the absolute frame.
QuoteIf you increase the acceleration force, the rod with the large mass on the end will lengthen more than its partner, whereas if you decrease the force, it will shorten more than its partner, which means the end of the rod without the mass on its end will move relative to the mark.That it will, but our example has constant acceleration of the ship, so the marks remain aligned forever.
QuoteThe solution to this though is to recognise that while the force changes due to length contraction/extensionNo it doesn’t. The force never alters. The force is a function of acceleration, not of speed, so it never wavers for any given point on the ship or a rod. It is different at one point than another, but always constant at a given point.
Quote from: Halc on 25/10/2018 02:03:59They can’t detect motion at all, and for all they know (without a window), they’re sitting in a building on a planet. They detect a force, and that’s it.Coincidence that the two cases look the same. The physics is very different as no length contraction is involved in the gravity case.
They can’t detect motion at all, and for all they know (without a window), they’re sitting in a building on a planet. They detect a force, and that’s it.
Quote from: HalcThis is incorrect. Both increase the acceleration (edit: deceleration).If contraction acts on the rearward-pointing rods, the ends are pulled in towards the ship. If extension acts on them, the ends are pushed out away from the ship.
This is incorrect. Both increase the acceleration (edit: deceleration).
If you're analysing events from the absolute frame and you start with the ship at rest, when the acceleration begins, we get a contraction which means that the ends of the rearward-pointing rods must be accelerating more. In the opposite case where the ship is moving backwards at a constant speed, then decelerates (while thinking it's accelerating forwards), the extension of the rearward-pointing rods must reduce the acceleration acting on their outermost ends.
There are two factors involved in producing the acceleration force - one is the constant acceleration of the ship and the other is length contraction/extension. The latter one will be visible to observers at rest in the absolute frame and they will see the truth of what is going on, but they will not know it to be the truth as they won't know which frame is the absolute frame.
Quote from: David Cooper on 25/10/2018 18:59:19The physics is very different as no length contraction is involved in the gravity case.Of course there is, else you’d have a local test for dilation when light speed is measured at greater than c in a gravity well because clocks run slow down there but the lengths are unaltered.
The physics is very different as no length contraction is involved in the gravity case.
Quote...The physics is very different as no length contraction is involved in the gravity case.Of course there is, else you’d have a local test for dilation when light speed is measured at greater than c in a gravity well because clocks run slow down there but the lengths are unaltered.
...The physics is very different as no length contraction is involved in the gravity case.
QuoteQuote from: HalcThis is incorrect. Both increase the acceleration (edit: deceleration).If contraction acts on the rearward-pointing rods, the ends are pulled in towards the ship. If extension acts on them, the ends are pushed out away from the ship.Yes, but all that reduced deceleration was done when the ship started decelerating and the ends of the R rods were allowed to continue at a greater speed than the already decelerating ship.
The force (the push for extending that you’re talking about) is a function of the second derivative of speed, not the first derivative. That means it is felt when the ship starts accelerating/decelerating, but during steady deceleration, that component is absent and all you have remaining is the R ends going faster trying to slow down (tension) to match the ship’s speed, which they will when it gets to the absolute frame.
The F rods initially decelerated to a speed less than the ship (momentarily reducing the steady state compression from a nonzero second derivative), but after that (steady state) spend their time decelerating less until the ship speed falls enough to match it.
They’re going faster and have to stop at the same time as the ship, so they have to be decelerating more than the ship, not less.
You asked for my opinion. That’s it, and it is with my etherist hat on as best I can.
Quote from: Halc on 25/10/2018 22:42:44Of course there is, else you’d have a local test for dilation when light speed is measured at greater than c in a gravity well because clocks run slow down there but the lengths are unaltered.I'm not talking about a detectable difference, but an underlying one. In the acceleration case, you get more and more length contraction the longer you go on accelerating. If you're just sitting on the surface of a planet, you get no change in length no matter how long you sit there.
Of course there is, else you’d have a local test for dilation when light speed is measured at greater than c in a gravity well because clocks run slow down there but the lengths are unaltered.
The reduced deceleration acts for as long as the ship is decelerating, and the rods continue to extend in length until the point where no contraction is acting on them, at which point they are at maximum distance from the centre of the ship.
That can't be right because when the deceleration of the ship become acceleration (when it is momentarily at rest in the absolute frame, the extension turns into contraction.
I wasn't discussing the ship stopping, but clearly if you switch the rockets off during acceleration,
Under deceleration (which still feels like acceleration to the people in the ship),
so when the rockets are turned off, what happens? Do the people in the ship measure a momentary deceleration of the ship in the former case? Of course, there's tension in the rod when the rockets are firing, so the mass will always pull the ship towards itself a bit when the rockets are switched off because that tension force has to be removed, but in one case there will be a tiny bit of extra force added to that, while in the other case it will subtract instead.