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Old Jul 21st 2015, 01:33 PM   #21
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Originally Posted by topsquark View Post
It looks to me that you are walking down the same road as Ernst Mach. Mach's principle deals with how the inertia of an object is defined in terms of the distribution of distant masses. Mach's principle was shown to be false by GR (Einstein backed Mach's principle until it was shown to be incompatible with GR.)
-Dan
I have now spent some more time looking into Mach's principle. The situation seems less straightforward than you suggest. Googling "Mach's principle springer.com/cda/content" reveals a very interesting article that you would understand much better than I.

However, I take a different approach to Mach on the issue of Newton's spinning bucket. The following is an extract from the 5th page of the Special relativity article on my site:

"It seems to me that spin is absolute because the universe’s motion energy is at a minimum. If we measure our planet to be spinning, but say instead that the universe is spinning, this would imply that the universe has immense spin energy. Observers on a faster spinning planet could say it has even more energy. But it would make more sense for all observers to agree that the universe is not spinning. So the idea of minimizing total motion energy defines a preferred and absolute basis for judging motion. In particular, observers are absolutely at rest if they see equal red shifts of light in all directions. Otherwise, they are travelling in relation to the observable universe. This seems to be a pretty good definition of absolute motion - despite what Einstein said. If we accept that absolute motion in relation to the observable universe can, in principle, be measured then the problem of multiple and equally valid realities can be avoided."

In order for the universe to have zero energy overall (otherwise how did it arise from nothing?) its energy must be conserved as zero. Energy conservation is of course not possible under SR, nor I presume GR. But if we accept the conservation laws rather than relativity, we need not be concerned how distant masses might physically impose absolute spin on us. The evolution of the universe ensures that this is the case.
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Old Jul 21st 2015, 10:52 PM   #22
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@AndrewS: whats your interpretation of the results of the michelson - morley experiments?

https://en.m.wikipedia.org/wiki/Mich...ley_experiment

it seems if we have a constant velocity v=c for light and that v=s/t (distance / time) then the only way to make C same for all observers is to "meddle" with both s *and* t.
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Old Jul 22nd 2015, 04:12 AM   #23
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Not being a physicist, I interpret the MM experiment in a very mundane way. I assume the speed of light is related to the medium it travels through; it slows down in glass, water etc. So I just assume light travels through the air/apparatus of the experiment at a constant speed irrespective of direction. I think the speed of light is also influenced by the local gravitational field. However I do not have access to the experimental findings that might allow me to disentangle the effects of gravity from that of the medium.

Now it’s my turn to ask a question concerning the speed of light. Imagine an astronomer who is not far from the equator. He is the first person to see a new supernova, just before dawn. Suppose the Earth is at a constant distance from this star. The Earth’s rotation means that the astronomer is travelling at a speed of v away from the star. If Einstein is right about the speed of light being constant for every observer, light will have to travel through space at a speed of c + v. This allows it to catch up with the receding astronomer at a net speed of c. The excited astronomer now informs another observatory about the supernova. This observatory is also not far from the equator but is thousands of miles away and here night has just fallen. Astronomers here are moving toward the star at v, so light from the star has to travel at c – v in order that it is seen to arrive at a speed of c. Here though, the event cannot yet be seen.

The speed difference between the observers (2v) is about 1 km/sec so the difference in light transit times is about 1 part in 300,000. For a stellar event that is only 1000 light years away, light from the same event would be delayed by only 29 hours, but for an average galactic distance it would be weeks or months. Extra-galactic events would be separated by years. Observations would also be much more affected by the Earth’s orbital speed which is about 60 times its equatorial spin speed. Astronomers could then re-observe events using more modern equipment than existed when the event was first seen by astronomers who were approaching the event. The phenomenon of distant events being seen to repeat themselves continually for years would be a spectacular demonstration of one of Einstein’s assumptions, yet I have never heard anything about it.

As with the spring paradox, we can also consider the viewpoint of stationary observers, this time at the Earth’s poles, but I do not see how this helps. For them the supernova is supposed to be further away. The event will be more delayed than the average delay for equatorial observers. Of course, I may have made a mistake somewhere. So apart from the other unresolved paradoxes and problems with special relativity, please can someone tell me why the above is not another reason to abandon the theory?
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Old Jul 22nd 2015, 02:25 PM   #24
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This so-called "paradox" really has nothing at all to do with GR, or SR, or anything more complicated than Newton's Laws. Let's consider a slightly different example involving an an ice skater, on Earth. Imagine the skater is sent gliding over the ice by the energy of a compressed spring attached to the building itself. After the energy of the spring is released and the skater has accelerated to velocity v in accordance with 1/2 kx^2 = 1/2 mv^2 the skater is in an inertial frame, as is the building. Someone standing on the ground next to the ice rink measures the skater's velocity as v and concludes the skater's KE is 1/2mv^2. But the skater considers himself at rest and the building - indeed the entire Earth- is moving in the opposite direction at speed v, so he concludes that the energy of the system is 1/2 Mv^2, where M is huge - trillions of tonnes. Obviously he has a very different view of the energy of the KE in the system. How do you solve this paradox? If you can't explain the solution to this then don't bother playing around with nuances of small mass changes that may occur under SR. The answer has to do with the fact that since v is not absolute but is relative, so is KE - there is nothing that says that different observers have to agree on the KE of an object.
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Old Jul 22nd 2015, 05:19 PM   #25
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Thanks for your response. You are of course correct that the energy scale is irrelevant. In my article I immediately follow the spring example with something a bit like your skater. I imagine a rocket crew who calculate how much fuel they will need to accelerate to a high speed. SR though leads them to believe that this fuel was instead sufficient to accelerate the whole universe to the same speed.

Whereas most people may think it would be ridiculous to compare the KE of a rocket with that of the universe, the spring example demonstrates that SR can lead observers to make conflicting predictions in any experimental situation where there is a change in KE.

I do not agree though that this situation is no more complicated than Newton's laws. These are consistent with the conservation laws and so do not lead to conflicting predictions.

Apart from the conflicting predictions involving KE, SR of course requires us to believe that an object can simultaneously have many sizes. This in itself would be paradoxical except that one can say SR requires us to live in different universes. This means we an each have our own version of each object, so the illogicality of an object simultaneously having different sizes can be avoided. Difficulties though arise when we experience an acceleration (or we live on a rotating planet that is accelerating toward the Sun). This means that between any inertial frames that we may fleetingly inhabit, the size of our own personal objects can change. Presumably physicists can still defend this interpretation because physics is not built on a principle of conserving size. However, by treating speeds as equivalent, the branch of physics occupied by SR defies the conservation laws that physics is based on. This is what I find paradoxical.

I do not expect those versed in physics to agree that there is anything paradoxical about this. If though you have time to read the two page article freephysics.uk/relativity-and-logic-01.pdf I hope you would see why I think this leads to a logical difficulty.

Assuming we agree to differ on the relevance of energy conservation, I would be interested to hear your views on the strobe paradox, the blue shift observed by a speeding observer and the constancy of the speed of light as these do not involve the issue of the conservation laws.
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Old Jul 23rd 2015, 12:26 AM   #26
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My input to this thread has so far been limited to pushing in the direction of a viable initiation mechanism, not discussing the application of (special) relativity.

Introducing an atomic bomb is one way to provide such a mechanism, though simple providing the astronauts with a precompressed spring is another.

You say that you understand SR, yet apply it to accelerating bodies.
Why?


https://en.wikipedia.org/wiki/Inerti...e_of_reference


Yes SR is applicable (and has been tested) at very small scales - you should look up mass defect and binding energy.

http://physics.bu.edu/~duffy/sc546_n...ss_defect.html

https://en.wikipedia.org/wiki/Nuclear_binding_energy

This was one of the earliest verifications of the mass-enery equation.
But even in chemical equations (reactions) there can be a mass defect effect.

To echo and extend Chip's theme from post 24

Energy is not a preserved quantity under relativistic transformations, but (4) momentum is.

Last edited by studiot; Jul 23rd 2015 at 01:56 AM.
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Old Jul 23rd 2015, 03:20 AM   #27
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Originally Posted by studiot View Post
Energy is not a preserved quantity under relativistic transformations, but (4) momentum is.
Hi studiot, thanks for rejoining the debate. I'm honoured to be facing the forum's big guns.

I have said I do not understand GR, but I don't think I have claimed to understand SR. In the spring example I am comparing the energies that would be measured in the inertial frames before and after the acceleration, not during. Non-physicists would expect this is a reasonable thing to do. It seems though that we can now agree that the principle of relativity defies the principle of energy conservation. Non-physicists find this very surprising. The point we still disagree on is whether this means current physics is logically consistent.

I have looked at your link to the binding energy of molecules but I do not see its relevance. I agree that E=mc^2 though I do not think it is valid to derive it from SR. Vibrating atoms with their orbiting electrons are always accelerating, and I thought we have just agreed that SR is then inapplicable.

As with Chip, I now invite your comments on the issues which do not involve the conservation of energy.
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Old Jul 23rd 2015, 03:47 AM   #28
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Once again you are addressing statements I didn't make.

The point we still disagree on is whether this means current physics is logically consistent.
I haven't agreed or disagreed only asked you to correctly follow the physical procedures and calculations before stating conclusions.
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Old Jul 23rd 2015, 04:27 AM   #29
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You're right. From your defence of SR I had assumed you think it is logically consistent. So do you agree it is inconsistent?
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Old Jul 23rd 2015, 12:29 PM   #30
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I think the argument put forward here (in past posts) is that SR is no more "inconsistent" than Newtonian mechanics. Different observers will make different measurements for the same physical phenomena in both. (Ie energy).

SR is not valid *at all* when acceleration is present. (Thats why I persevered for so long with the CADO equations, which can be applied to GR, with @MikeFontenot on this forum. )

@AndrewS: I am not clear what you are finding exception to? Is it something more than different observers making different measurements?
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