# Question regarding Relativity.

Discussion in 'General Science & Technology' started by Equinox, Nov 29, 2017.

1. ### EquinoxRegistered Senior Member

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In regard to relativity - as I understand it, the faster you move the slower time becomes, so a person moving at light speed would perceive time to stop, whilst an outside observer would be unaffected.

So my question is this... do you need to move 'through' space for this phenomena to occur?

If it was possible to create a machine that could 'spin' you at the speed of light whilst remaining stationary (ignoring for the moment the technological limitations of such a device and assuming they could survive the G forces). Could a person enter such a device and be 'spun' for 1000 years and not age, whilst the people in the laboratory around it would age as normal?

Or does one have to move from point 'A' to point 'B' for these relativistic effects to occur?

The reason why I ask is because I was reading about how black holes would affect an 'inside' and 'outside' observer - the black hole is stationary but for the person who enters it - time stops, even though the black hole is spinning but 'stationary'.

Could a person enter a device as described above - stop time for themselves, and then step out again into the future?

Apologies if my question is simplistic - I love learning about science but some concepts I find hard to get my head around.

Edit: Just realised Blackholes are less to do with spin and more to do with density affecting time/space around them so my comparison may seem erroneous. Still I would still like to know if the original question has any merit - do you need to move through time AND space to experience relativistic phenomena?

3. ### Q-reeusValued Senior Member

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3,170
Your profound misunderstandings of what special relativity is all about may be resolved by watching this YT vid:

5. ### EquinoxRegistered Senior Member

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106
Thank you for the very informative video.

However it did not answer my question as each and every example involved 1 moving and 1 stationary person/object.

My question was in regard to 'spinning' at the speed (or near speed) of light.

This would mean both people are stationary but one of them is spinning at the speed of light but not leaving the actual location.

Forgive me for my ignorance.

7. ### EquinoxRegistered Senior Member

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106
P.S: I had already pointed out that I do not understand the principles of relativity, particularly in regard to the specific scenario of 'stationary' objects/people that I described.

I'm not quite sure how labelling my question as a 'profound' misunderstanding is necessary - particularly as I have pointed out I have limited knowledge of the topic and was reaching out to find out more.

8. ### Q-reeusValued Senior Member

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Ah ok - 'spinning' motion is the main issue. Well orbiting motion of an observer breaks the symmetry of time dilation applying to uniform relative motions. In such a way that from the pov of someone orbiting in a circle, everyone else's clocks are running fast not slow. Similarly, everyone else (not 'spinning' or in relative linear motion) will agree the orbiter's clock is running slow. The formal explanation for this profound difference to the case of relative linear motions is to be found by application of the principle of the spacetime interval, shown for case of motional effects only here:
https://en.wikipedia.org/wiki/Clock_hypothesis

It's a bit tricky because one could argue there is still reciprocity of relative motions but the absence of centripetal accelerations for the 'stationary' observers means circular motion is 'absolute' in a fundamental sense. Anyway yes in principle orbiting at high speed provides a kind of 'time-machine' or perhaps better termed a hibernation machine.

9. ### EquinoxRegistered Senior Member

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106
Ok thanks again for the informative reply - to give you an idea of the 'machine' I had in mind (there are 2) the first one is this:

The second one is this:

In one of them you turn in circle and actuall have a small circumference of movement - in the other you actually move but you don't actually 'go' anywhere.

So if you where to 'spin' at near the speed of light in either of these devices - time would slow dramatically for yourself but not for the outside observer?

I'm trying to understand if large amounts of actual'space' (great distances between point 'A' to point 'B') are necessary for relativistic phenomena to occur, if that makes sense.

Last edited: Nov 30, 2017
10. ### Q-reeusValued Senior Member

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3,170
The first example - a centrifuge - will in principle give you what you want. Except the relative time slowing is infinitesimal and would likely amount to ~ mere microseconds over a lifetime. Not exactly 'value for money'! The second example looks like a gimbal arrangement designed to create nausea - best avoided imo!

As for 'time slowing for yourself' - recall in that vid that proper time - the 'rate-of-time-flow' experienced by you regardless of your motion relative to anyone else - is always the same.
That doesn't change in the case of circular motion. What changes is the measurement (or perception) of clock-rate of others moving differently to yourself.

11. ### Write4UValued Senior Member

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9,500
One thing I find curious.
At Cern they are able to achieve a "closing speed" greater than "c". What happens to time or space in between the approaching particles?

12. ### arfa branecall me arfValued Senior Member

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That's easy. As far as the rest frame of the accelerator, nothing happens. But the opposing beams are in their own spacetime slice, each distinct. For the beams the space between the "approaching" particles is practically nonexistent.

Complicating things is the fact the beams are oscillating in a resonant way relative to the rest frame.

13. ### Write4UValued Senior Member

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9,500
TY for your response. Would this resonance have anything to do with the particle/wave function?

14. ### Q-reeusValued Senior Member

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3,170
Firstly, what does 'a closing speed greater than c' even mean? My guess is the scenario in mind is where counter-propagating ultra-relativistic protons or such collide in the LHC rest frame. Relativistic velocity addition doesn't work the way you think it should. From the rest frame of either proton say, the other one is still moving with a closing speed v < c. Nothing profound happens in the space between them - at least until actual collision produces the usual fireworks.

15. ### Write4UValued Senior Member

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Ah, I never had any problem with the concept of the person walking or running up an escalator moving at "c" and always getting to the top at the same time. But that would involve only one direction.
Thus my question about what would happen in a scenario with two escalators, one going up and the other going down @ "c". If persons going in opposite directions would pass each other halfway at half the time..

At less than "c" this would happen between, say two cars travelling @ 50 mph , their closing speed would be 100 mph.

Last edited: Nov 30, 2017
16. ### arfa branecall me arfValued Senior Member

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Maybe. I think classically it has to do with charged particles conserving angular momentum in a magnetic field.

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17. ### Q-reeusValued Senior Member

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Yes but that is merely a very good approximation when relative speeds are << c. If not, like at CERN LHC scenario, one has to use relativity:
http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/einvel2.html

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