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Offline DoctorBeaver

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time v speed of light
« on: 18/05/2006 22:02:23 »
I regret that I'm not a good-enough physicist/mathematician to work this out for myself so, hopefully, 1 of our resident genii will supply an answer.

It's accepted that the speed of light is constant (to all intents & purposes) & time is relative. Is there anything in relativity that says this must be the case? Does the maths of relativity allow for time being constant & the speed of light being relative?

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Offline PrajnaDhyana

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Re: time v speed of light
« Reply #1 on: 19/05/2006 01:31:07 »
To put it into very general terms, the reasons why time is relative prevent it from being a constant.

Most people think of time in terms of a river, where we are stationary and time is endlessly flowing past us.  Relativity paints a picture of time as more of a road, where time is stationary and we are the ones moving.  Past, Present and Future are all the same thing, it's the way we perceive  time that makes them seem different.  How we interact with time effects how fast or slow it “flows”.  As we move down the “road” of time, we can do things that speed up or slow down our movement down this “road”.  This explains why two different people can experience the flow of time differently.  They are moving at different speeds down the “road”, so the “road” appears to “flow” past them at different rates.  The “road” itself (time) doesn't change, what changes is how we experience it.  Since it doesn't seem possible to make everything in the Universe move down this “road” at exactly the same speed, time can't be a constant.  

On a related note, not only is time not a constant, but space isn't one either.  The distances between points in space literally change depending on how fast you are traveling (the faster you go, the shorter the distance).  For some reason, only the maximum speed of light seems to be constant.
 
It also appears that for certain sub atom particles there is no “arrow of time”.  They seem to be able to freely move forwards and backwards through time "at will".  From their point of view I imagine the concept of time is meaningless.
 

Offline Atomic-S

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Re: time v speed of light
« Reply #2 on: 19/05/2006 06:33:51 »
One other detail that must be recognized to get any right understanding of this subject, is not only are time and space of different scale for different observers, they are in general interconverted into one another, so that what appears to one observer as time, will appear to another to be a combination of time and space. Similarly, what seems to one observer to be simply a spatial distance, to another may appear as a combination of a spatial distance and a temporal interval. The exact relationships describing these things for the case of special relativity, for the simple case where the coordinate axes of a moving and stationary observer coincide at some place and moment, and the moving observer mives with uniform speed v in the x direction, are:

x' = (x - ct)/sqrt(1 - v^2/c^2)
y' = y
z' = z
t' = (t - vx/c^2)/sqrt(1 - v^2/c^2)

You will note that the formula for x' is a function of both x and t; and likewise for the formula for t'.  Thus, by moving, the observer alters his "orientation" with respect to space and time, so that what appeared before to be pure space, is now space and time both; and likewise for time.

Another peculiarity requiring attention is that in general relativity, time is subject to other forms of distortion, with the result that the speed of remote light may appear to have a different speed than that of local light.
 

Offline Atomic-S

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Re: time v speed of light
« Reply #3 on: 19/05/2006 06:35:14 »
Escuse me; I made a mistake on one of those formulas. It should read:

x' = (x - vt)/sqrt(1 - v^2/c^2)
 

Offline Roy P

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Re: time v speed of light
« Reply #4 on: 19/05/2006 12:13:26 »
quote:
Originally posted by Atomic-S

Another peculiarity requiring attention is that in general relativity, time is subject to other forms of distortion, with the result that the speed of remote light may appear to have a different speed than that of local light.

This sounds fascinating, Atomic! Can you elaborate -- in layman's terms?

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Offline DoctorBeaver

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Re: time v speed of light
« Reply #5 on: 20/05/2006 14:23:41 »
I think I follow what you've all said (although the maths made my eyes glaze over).

I'm well aware of the perception of time passing at different rates. Wasn't it Einstein who said words to the effect of "An hour in the company of a beautiful woman seems like a minute, but put your hand in ice for a minute & it seems like an hour"?

However, I'd like to go back to what PrajnaDhyana said about time being like a road. Does it need to be a flat, uniform road? What if there were places where it was elongated? Or maybe a better analogy for what i'm thinking would be to liken it to a river. There could be places where the river runs faster (for instance a more steep decline, or a narrowing of its flow). If we were in a real river, we would only notice the increase in speed by the passing scenery. However, if we were in a river of time, would we be able to detect if it were, in fact, flowing faster? If an event takes a nansecond to occur and that nanosecond was stretched by 50% it would still only be a nanosecond to us so we wouldn't detect a change.

Oh how I wish my imagination was limited by vocabulary! [:(!]

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Offline PrajnaDhyana

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Re: time v speed of light
« Reply #6 on: 21/05/2006 13:55:15 »
I used the term “road” extremely loosely in my example. I was using the term “road” as an analogy to help illustrate a very abstract idea more than as an actual representation of what time is.  If it helps you to think of it more as a river that you are floating on, that's just as good.  It was a way of showing that time isn't a thing that is moving past you any more than “up” is a thing moving past you.  Time is really just another dimension of space through which we move.

If you think about it, you can't really see the dimension “up”.  Sure you can tilt your head back and look upwards, but can you actually see what “up” is?  The only thing that makes “down” different from “up” is your orientation.  If you are standing on a ladder a few rungs above another person you are both existing in the same spacial plane, but they are Down for you and  you are Up for them. Up and Down are really the same thing, just seen from different directions.  The same goes for time.  We can see the effect of moving through it, but we can't really see what it is we are moving through. Future and Past are the same thing, just seen from different perspectives.  Albert Einstein and all of us exist in the same temporal plane, but he is Past for us and we are Future for him. One could say that Albert and all of us exist simultaneously, but because of the limited way we perceive time it seems as though we are separated. At this moment, Albert is just as alive as we are, but is in a different temporal “place”.  Just as my sister occupies the same temporal position I do (“now”), but lives in a different spacial position (a different city). I can't see her, but she's there none the less.

One of the weird things that quantum mechanics has shown us is that sub atomic particles are constantly coming into existence, seemingly from nothing, then exist for the smallest amounts of time imaginable, then vanish again into nothing.  I would suggest to you that this might be because they move through time at a different rate than we do (and/or even a different direction).  We can only perceive them when they pass through the same “slice” of time that we are currently in. So it appears to us that they materialize out of nothing, then vanish back into nothing, when in fact they have a continuous existence through space and time just as we do.

Why does time only flow in one direction for us then?  Theoretically it is possible to move backwards through time.  It's just that it's so difficult to do that for all intents and purposes it's impossible for us to do so.  Once again we can use an analogy involving movement through space to show why, and again this is a very loose analogy.
 
Imagine that you are sliding down a huge, super smooth, nearly frictionless piece of transparent metal.  There is just enough friction between you and the metal so that you slide downward at a constant rate instead of accelerating.  If you press your hands against the plate you can only generate enough friction to just barely feel it, but not enough to slow yourself down.  So you can feel the plate sliding past, but can't interact with it in any other way.  If you could find a way to press down hard enough you could  eventually stop yourself, or even go so far as to start climbing back up.  The problem is that you can't press down hard enough to do this.  Now we know that energy and mass are the same thing, so as you create energy your mass increases and you press down on the plate a little harder.  The more energy; the more mass; the harder you press down; the slower you go.  Eventually if you could create enough energy your mass would get so great that you would press down hard enough to stop. Add a bit more, and you could start to move back up the plate.  The big problem is that we don't have any way of creating the astronomical amounts of energy needed to do this.  Or even enough energy to slow us down enough to be noticeable.

And if that wasn't confusing enough, string theory brings at least six other spacial dimensions and possibly even parallel Universes into the mix!  NOVA did a nice three part series on this called The Elegant Universe.  You can watch it online here: newbielink:http://www.pbs.org/wgbh/nova/elegant/program_d.html [nonactive]
« Last Edit: 22/05/2006 00:25:52 by PrajnaDhyana »
 

Offline Roy P

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Re: time v speed of light
« Reply #7 on: 21/05/2006 14:56:19 »
I can actually understand what you're saying, Prajna. I like your style :) and I've bookmarked your excellent link.

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Offline DoctorBeaver

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Re: time v speed of light
« Reply #8 on: 21/05/2006 22:42:42 »
quote:
Originally posted by PrajnaDhyana


One of the weird things that quantum mechanics has shown us is that sub atomic particles are constantly coming into existence, seemingly from nothing, then exist for the smallest amounts of time imaginable, then vanish again into nothing.  I would suggest to you that this might be because they move through time at a different rate than we do (and/or even a different direction).  We can only perceive them when they pass through the same “slice” of time that we are currently in. So it appears to us that they materialize out of nothing, then vanish back into nothing, when in fact they have a continuous existence through space and time just as we do.



Interesting. I have often wondered if it's possible to travel "sideways" through time.

quote:

And if that wasn't confusing enough, string theory brings at least six other spacial dimensions and possibly even parallel Universes into the mix!  NOVA did a nice three part series on this called The Elegant Universe.  You can watch it online here: http://www.pbs.org/wgbh/nova/elegant/program_d.html



I'm familiar with string theory & I've seen "The Elegant Universe" on TV. It was a fascinating series & presented in a way that was comparatively easy to follow. BUt does string theory have anything to say about time? I've not come across that.

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Offline PrajnaDhyana

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Re: time v speed of light
« Reply #9 on: 22/05/2006 01:13:20 »
I am not versed enough in string theory to say for sure if it deals with the concept of time or not.  But from what I know about it I would say that it does.  However I don't think it treats it as anything special.  It's just another spacial dimension among many.  I believe it treats it the same as it does up and down, left and right, forwards and backwards (or any of the other six or so dimensions).  

quote:
Interesting. I have often wondered if it's possible to travel "sideways" through time.
 

First I should point out that my little suggestion about how sub atomic particles can seem to wink in and out of existence does have some flaws to it, which is why I used the words “suggest” and “might”.  Although I do think it might be part of what causes this phenomena, it seems that there must be more to it than just that.

As to whether it's possible to move sideways through time, I would say that it's not.  I will once again compare it to up and down to show why.  It's not possible to move sideways through “Up” because once you change directions you would be moving in a different dimension, i.e. you would start to move left, or forward, etc.  The same goes for time. If you started to move sideways through time it seems that you would then be moving through a different dimension, maybe even one of the other six that string theory predicts.  You can only move through each dimension a certain way and once you change how you move, you change which dimension you are moving through.

But since this is pure conjecture and there is no way to test this thought, we have left the realm of science and are now firmly in the field of philosophy.  Not that it's a bad thing to philosophize, it's just that without any kind of experimental proof one opinion is just as valid as the next.  Ultimately it's all just guess work when you reach this point.
 

Offline DoctorBeaver

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Re: time v speed of light
« Reply #10 on: 22/05/2006 11:07:03 »
Maybe saying "sideways in time" was incorrect. I should have said temporal dimensions at "rightangles" to the 1 we percieve. There are 3(that we know of) spatial dimensions. Why not 3 temporal dimensions too? I don't have a problem conceiving that they may exist although I cannot even begin to understand how they would work.

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Re: time v speed of light
« Reply #10 on: 22/05/2006 11:07:03 »

 

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