A thought Experiment in Time Dilation

[just dave]

TL;DR Summary

Something I thought of years ago that no one has answered.

Ok so here's my idea,it came to me while watching a record album spin on my turntable(I believe it was Dark Side of the Moon). Technically this exp. could be done now but the results would take a while.
You take a disc of some super strong material attach it to a ultra high RPM motor and put it in a vacuum chamber.Then spin it up to billions of rpm.Now a point near the center of this disc will not be moving very much but on the edge it's moving a lot.
Depending on the size (say it's 10 ft. in circumference) and it's speed (say 1 billion rpm) the edge of the disc is moving at 17% of c. So time slows down more on the edge of the disc then the center.Does the edge of the disc begin to disappear due to Time Dilation? How far back in time would it have to go before you noticed any effects?
Now I know there's no material strong enough to withstand the centrifugal forces or a motor that can rev up that high,that is why I called it a thought exp.This exp. could be done now but at a much slower speed and would have to run for years.
So what do you think?

 

[PeroK]

Summary:: Something I thought of years ago that no one has answered.

Ok so here's my idea,it came to me while watching a record album spin on my turntable(I believe it was Dark Side of the Moon). Technically this exp. could be done now but the results would take a while.
You take a disc of some super strong material attach it to a ultra high RPM motor and put it in a vacuum chamber.Then spin it up to billions of rpm.Now a point near the center of this disc will not be moving very much but on the edge it's moving a lot.
Depending on the size (say it's 10 ft. in circumference) and it's speed (say 1 billion rpm) the edge of the disc is moving at 17% of c. So time slows down more on the edge of the disc then the center.Does the edge of the disc begin to disappear due to Time Dilation? How far back in time would it have to go before you noticed any effects?
Now I know there's no material strong enough to withstand the centrifugal forces or a motor that can rev up that high,that is why I called it a thought exp.This exp. could be done now but at a much slower speed and would have to run for years.
So what do you think?

What are you expecting to happen?

All others things being equal, the edge of the disc would age slower than the centre. E.g. if you had a radioactive isotope on the edge and at the centre, the isotope on the edge would decay more slowly.

 

[Dale]

Summary:: Something I thought of years ago that no one has answered.

Does the edge of the disc begin to disappear due to Time Dilation?

No. clocks on the edge go slow but they don’t disappear. This experiment has been done using Mossbauer rotors, not as fast as you mention, but fast enough to observe relativistic effects on the edge.

 

[just dave]

What are you expecting to happen?

All others things being equal, the edge of the disc would age slower than the centre. E.g. if you had a radioactive isotope on the edge and at the centre, the isotope on the edge would decay more slowly.

I want to know would you see the edge start to disappear as it slips back in time,in effect,seeing Time Dilation right before your eyes. I think that would be pretty cool no?

 

[Ibix]

Does the edge of the disc begin to disappear due to Time Dilation? How far back in time would it have to go before you noticed any effects?

Clocks on the rim of the disc would tick slowly, that's all (about 1 second per 1.01s as measured by stationary clocks in your example). There's no "going back in time" here.

It's worth noting that describing a rotating disc in special relativity can get quite complicated. In fact, developing understanding of it was one of the threads that led to general relativity.

 

[just dave]

No. clocks on the edge go slow but they don’t disappear. This experiment has been done using Mossbauer rotors, not as fast as you mention, but fast enough to observe relativistic effects on the edge.

Do you have a website or link to this experiment?

 

[just dave]

Clocks on the rim of the disc would tick slowly, that's all (about 1 second per 1.01s as measured by stationary clocks in your example). There's no "going back in time" here.

It's worth noting that describing a rotating disc in special relativity can get quite complicated. In fact, developing understanding of it was one of the threads that led to general relativity.

Not exactly going back but slowing down compared to the rest of the disc.

 

[Dale]

Do you have a website or link to this experiment?

The reference is
Kuendig, Phys. Rev. 129 no. 6 (1963), pg 2371.
But I don’t have a link

 

[PeroK]

I want to know would you see the edge start to disappear as it slips back in time,in effect,seeing Time Dilation right before your eyes. I think that would be pretty cool no?

Why would it disappear? It would simply in physical terms age less than the centre.

 

[Ibix]

The reference is
Kuendig, Phys. Rev. 129 no. 6 (1963), pg 2371.
But I don’t have a link

Abstract is here: https://journals.aps.org/pr/abstract/10.1103/PhysRev.129.2371. You have to pay for the article - but some publishers are doing special access while COVID19 is around. Dunno if that applies here.

 

[Ibix]

Not exactly going back but slowing down compared to the rest of the disc.

Clocks on the rim will tick slowly, that's all.

It's more complex because gravity is involved, but GPS satellite clocks have a tiny correction due to relativistic effects, including this same effect. They don't fade from view or anything.

 

[just dave]

Why would it disappear? It would simply in physical terms age less than the centre.

Because it is slipping out of the present as we watch it.Time is continuing at a "normal" unaccelerated pace for us and the center of the disc.

 

[PeroK]

Because it is slipping out of the present as we watch it.Time is continuing at a "normal" unaccelerated pace for us and the center of the disc.

That's not what time dilation is about.

 

[Dale]

Because it is slipping out of the present as we watch it.Time is continuing at a "normal" unaccelerated pace for us and the center of the disc.

Why would that make it disappear? It is still there, just at a different time according to its clock than according to ours.

If you and I meet and immediately look at our watches and they show different times that doesn’t mean that we didn’t meet, just that my watch said our meeting happened at a different time than your watch said.

 

[just dave]

Clocks on the rim will tick slowly, that's all.

It's more complex because gravity is involved, but GPS satellite clocks have a tiny correction due to relativistic effects, including this same effect. They don't fade from view or anything.

Yes I know and elementary particles live longer when traveling at relativistic speeds. What are clocks actually measuring though? Time or our idea of time?

 

[Dale]

What are clocks actually measuring though? Time or our idea of time?

What is the difference?

Whatever they are measuring it doesn’t involve things disappearing because it goes slow.

 

[just dave]

Why would that make it disappear? It is still there, just at a different time according to its clock than according to ours.

If you and I meet and immediately look at our watches and they show different times that doesn’t mean that we didn’t meet, just that my watch said our meeting happened at a different time than your watch said.

We are not physically connected.The disc started out in the same time frame but now part of it is ageing more slowly than the rest of it.

 

[PeroK]

What are clocks actually measuring though?

Generally they are counting occurrences of some physical process: the orbit of the Earth round the Sun, the Moon round the Earth, the rotations of the Earth on its axis, the swings of a pendulum, the oscillations of a quartz crystal, the transitions of a caesium atom.

 

[PeroK]

We are not physically connected.The disc started out in the same time frame but now part of it is ageing more slowly than the rest of it.

It's still physically there though!

 

[Dale]

We are not physically connected.The disc started out in the same time frame but now part of it is ageing more slowly than the rest of it.

That isn’t relevant.

Look, time dilation just doesn’t work this way. This has been done. There is no disappearing involved. Just discard that idea. I don’t know where you got it, but the world doesn’t work like that.

 

[just dave]

It's still physically there though!

Yes I get it but there would have to be some other effects on the rest of the disc then.

 

[DaveC426913]

Yes I get it but there would have to be some other effects on the rest of the disc then.

Certainly. It will experience stress and eventually disintegrate - for the same reason the string breaks in Bell's Spaceship Paradox.

 

[just dave]

Certainly. It will experience stress and eventually disintegrate - for the same reason the string breaks in Bell's Spaceship Paradox.

Assuming the material is strong enough to withstand the stresses from the high RPM. Would it fracture due to time dilation? Also I'm not familiar with Bell's Spaceship Paradox I'll have to look that up.

 

[DaveC426913]

Assuming the material is strong enough to withstand the stresses from the high RPM. Would it fracture due to time dilation? Also I'm not familiar with Bell's Spaceship Paradox I'll have to look that up.

From the length contraction.

The material along the circumference will shrink - pull away from itself.

Ah. Right. The circular configuration of Bells' Spaceship Paradox is called the Ehrenfest Paradox.
That's the one you want to look up.

And it looks like - in a realistic scenario - the disc might not actually shatter. (though the stresses due to length contraction are still present.)

 

[PeterDonis]

Would it fracture due to time dilation?

No. Time dilation isn't a force and it doesn't cause any mechanical stress.

 

[just dave]

That isn’t relevant.

Look, time dilation just doesn’t work this way. This has been done. There is no disappearing involved. Just discard that idea. I don’t know where you got it, but the world doesn’t work like that.

I guess I'm thinking more of going back in time, more like a time machine.

 

[Ibix]

Assuming the material is strong enough to withstand the stresses from the high RPM. Would it fracture due to time dilation? Also I'm not familiar with Bell's Spaceship Paradox I'll have to look that up.

In this context, all that happens is that clocks tick slowly, and length contraction means that the stresses on the disc are higher than a non-relativistic calculation would predict.

I guess I'm thinking more of going back in time, more like a time machine.

Seriously, all that happens is that the clocks on the disc tick slowly. It doesn't stop existing now or anything like that - you just have a thing that's younger than you would expect if you didn't know about time dilation.

 

[PeterDonis]

I guess I'm thinking more of going back in time, more like a time machine.

That isn't what time dilation is. No matter how many times you ask, that answer will not change.

 

[just dave]

No. Time dilation isn't a force and it doesn't cause any mechanical stress.

Even if time on the edge of the disc nearly stops? I would think that would have some physical consequence on the rest of the disc.

 

[PeterDonis]

Even if time on the edge of the disc nearly stops?

No.

I would think that would have some physical consequence on the rest of the disc.

It doesn't. Again, no matter how many times you ask, the answer will not change.

 

[just dave]

Hey just trying to learn something and maybe have an interesting conversation,buddy. Apparently no matter how many times I ask you will reply.

 

[PeterDonis]

Apparently no matter how many times I ask you will reply.

As long as you keep asking the same question, we'll keep giving the same answer, yes. But perhaps it would be easier just to close the thread at this point, so I have done so.