# The Naked Scientists Forum

### Author Topic: Decreasing in size at the speed of light  (Read 3617 times)

#### realmswalker

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##### Decreasing in size at the speed of light
« on: 27/11/2005 20:12:33 »
If you have a giant circular flat piece of metal, like billions of light years wide, and you cause it to shrink so that the edges are moving inwards at the speed of light (or close to it) what would happen...
The middle point would remain perfectly still, but would it all age the same speed or would the middle age much faster than the rest.
i guess its similar to what would happen if you have a rope on a tether spinning with a weight on one end with the outside part spinning at the speed of light. The closer to the tether the slower it would be traveling (because the rope travels less distance the closer it is to the middle).
Any one know what might happen in these scenarios?

#### tweener

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##### Re: Decreasing in size at the speed of light
« Reply #1 on: 28/11/2005 00:36:54 »
Interesting question - I would think that the equations governing this are relative to the observer, thus you have to define where the observer is located.  If the observer is at the center of the disk (the "still" place) then the outer edges would be aging according to relativity and as you looked farther in, each point would have a different rate of aging.  So, the aging would be changing over the surface of the disk.

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#### DoctorBeaver

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##### Re: Decreasing in size at the speed of light
« Reply #2 on: 28/11/2005 01:06:00 »
This could have horrible repercussions for ice-skaters spinning quickly! [:0]

Seriously, though, it's an interesting question. Relativity says that the edge should age more slowly than the centre,I think.

#### ukmicky

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##### Re: Decreasing in size at the speed of light
« Reply #3 on: 28/11/2005 02:12:36 »
The doc This could have horrible repercussions for ice-skaters spinning quickly!
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Wicked,.its the thought of all those young ice dancers with wrinkled olds hands
________________________________________________
realmswalker

How would it shrink so that the edges are moving in
Michael
« Last Edit: 28/11/2005 03:47:03 by ukmicky »

#### realmswalker

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##### Re: Decreasing in size at the speed of light
« Reply #4 on: 07/12/2005 01:58:40 »
itd be easier to see it demonstatred with 1dimensional object (a line)
if ---- = distance light travels in a second
and x's take up no space

it would look like this (this is just a short line, itd have to be way long)
x--------x--------x

to

x----x----x
« Last Edit: 07/12/2005 02:00:19 by realmswalker »

#### DoctorBeaver

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##### Re: Decreasing in size at the speed of light
« Reply #5 on: 07/12/2005 02:04:04 »
The speed of light is, apparently, not a limitation over massive distances. What would happen were the ends of the line far enough apart for this to be true? How would that affect the difference in speed of ageing?

#### Soul Surfer

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##### Re: Decreasing in size at the speed of light
« Reply #6 on: 07/12/2005 10:58:46 »
You should rephrase any questions like this in terms that were at least plausibly achievable.

If I get one of these big torches or a laser (which are both easily visible at very great distances) and spin round holding it what happens to the beam of light?

As an observer moves away, the beam of light is moving sideways faster and faster and must eventually exceed the speed of light?

no it just forms a pretty spiral.

There is an angular error on all telescopes called Aberration caused by the fact that the telecope has moved in the tile it takse for the light to pass from the lens to the eyepiece.  This has to be allowed for if you want to measure star positions very accurately in the sky to determine their distance using parallax.

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#### DoctorBeaver

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##### Re: Decreasing in size at the speed of light
« Reply #7 on: 07/12/2005 13:42:02 »
quote:
You should rephrase any questions like this in terms that were at least plausibly achievable.

Why?

I don't see the relevance of telescopes to this either.

#### Soul Surfer

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##### Re: Decreasing in size at the speed of light
« Reply #8 on: 07/12/2005 16:42:21 »
To go back to the original (and in my opinion) rather silly question. how do you know exactly how old a piece of metal is?

My first comments on this topic were related to addressing similar "problems" using a more practical experimental image.  The telescope example is a case in the real world where effects like this are relevant.

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#### The Naked Scientists Forum

##### Re: Decreasing in size at the speed of light
« Reply #8 on: 07/12/2005 16:42:21 »