Speed of Light

The non amateur stuff. Hawking, black holes, that sort of thing

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astronomerjim
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Speed of Light

Post by astronomerjim »

Just curious about this one... Was pondering in my head for a while.

So as we all know, as we approach the speed of light, time slows down...

Thought i've had is, as light is, well, travelling at the speed of light, it's time would be infinitely long wouldn't it? So the universe could be infinite?

M54
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Post by M54 »

The person travelling seems to be slowing down to an external observer.
The external observers time is still going at the "normal" rate.

To the traveller the people outside seem to go faster.
The traveller just sees themselves moving at the "normal" rate.

Whoever is "observing" only sees themselves as moving normally through time. What they are observing can appear to be going slower or faster through time.

What's the problem with the universe being infinite?
Makes sense for it to be so.

big_kev
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Post by big_kev »

M54 wrote:
What's the problem with the universe being infinite?
Makes sense for it to be so.
It makes no sense for the universe to be infinite.
Think of the consequences of this.

Mogget
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Post by Mogget »

It's also worth thinking of the consequences of a finite universe. I mean, what lies outside it? If your answer is "nothing", try to imagine what "nothing" would be. Seriously, it is just as difficult to accept a finite universe (or reality) as it is an infinite one.

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Post by joe »

I have no problem picturing a finite universe. If space was created with the universe then there can be no "outside". There would be no space for the "nothing" to exist in.
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big_kev
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Re: Speed of Light

Post by big_kev »

Back to the original question !
astronomerjim wrote:
So as we all know, as we approach the speed of light, time slows down...
Actually it doesn't slow down, it just appears to slow down.

Consider a clock in front of you ticking away in time with your wrist watch.
You look at your watch and then at the clock and they are knocking up the seconds at the same rate.

But what happens if the clock is moving ?

There is now a delay between one second and the next.
You will look at the clock initially to synchronise with your watch at say 12:00:00
Then when your watch reaches 12:00:01 you look at the clock but there is a delay due to the time taken for the signal to reach you from the clock.

As the clock moves away from you nearer to the speed of light the delay increases.

Hence you will think it is running slow in comparison to your watch.

An observer travelling with the clock would use exactly the same argument to say that your watch was running slow compared to his Clock.


Two assumptions are made here:
1: The speed of light is constant.
2: Neither the clock or your watch are accelerating


Note: The same is true for mass and length using the arguement above.
They do not increase/decrease dependant upon speed but remain constant.
They just appear to change....it would be nonsense otherwise.

Mogget
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Post by Mogget »

I have no problem picturing a finite universe. If space was created with the universe then there can be no "outside". There would be no space for the "nothing" to exist in.
Yes, but can we really understand the concept of "nothing"?

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Post by Quasar »

Mogget wrote:
I have no problem picturing a finite universe. If space was created with the universe then there can be no "outside". There would be no space for the "nothing" to exist in.
Yes, but can we really understand the concept of "nothing"?
You make the mistake of assuming nothing is a relative concept.
Take for example the Sun, the Sun has mass, density and size. How much Sun is past it's own size? obviously the Sun doesn't extend past its own boundaries so there is no Sun past it's own size. Imagine the Sun is the Universe, it cannot exist past it's own size or boundaries.
Many people seem to look at the Universe as a spherical window from which we can look outward into nothing, it is much easier to understand if you imagine the window from which you look is actually inside the Universe and everything you can see through it is always inside. There is no outside.

Mogget
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Post by Mogget »

Maybe I should clarify my position here. I have no problem with the universe having finite boundaries, but to say that there is "nothing" beyond it requires an understanding of "the absence of anything", and that is something that I don't believe any of us can truly grasp.

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Post by joe »

It's certainly a concept that requires some thought but maybe I'm not grasping it properly as I am relatively comfortable about an "absence of anything". Maybe some people think about it too much; a legacy of not quite accepting that the universe is all that there is, or an inability to escape the handicap (in this case) of having to visualise concepts. An absence of anything means that there is nothing to contemplate.
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Cliff
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Post by Cliff »

Dear Joe
I think I agree with you.
However, putting it crudely, in my opinion, the problem really is that
some people think that they (possibly not meaning them personally but humans) will eventually know the answer to everything.
Needless to say I think "they" are idiots.
My personal concept of "nothingness" or as near as I can get to it is when being dead. Of course the matter that makes me up or at least some of it (ie the stuff that makes me so good looking) will continue to exist. However, arguably the most important bit of me (the thinking bit) will disappear.
Of course it has occurred to me that possibly even the "thinking" bit might not disappear completely.
I have a pet theory that the collective growth of our thinking bits (not just humans but lets say all forms of life that dies) continues to exist as radiation that persists throughout the Universe.
Just suppose that the so-called CMB that cosmologists all rave about is not really what cosmologists assume it is.
I'll suggest it is really the cumulative bits of life thats now dead .
Of course that's nonsensical conjecture !!!!!!!!!!!!!!
Best wishes from Cliff

Quasar
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Post by Quasar »

Mogget wrote:Maybe I should clarify my position here. I have no problem with the universe having finite boundaries, but to say that there is "nothing" beyond it requires an understanding of "the absence of anything", and that is something that I don't believe any of us can truly grasp.
Oh it's quite simple Mogget, no matter where you look in the Universe you are always looking inward - never outward.
It isn't nothingness that people fail to understand but rather the shape of the Universe. We can never look outward because the Universe isn't outward shaped. It isn't outward shaped because there is only inward.
Most people imagine a scenario where they are a goldfish in a bowl. The water is the Universe and the glass is the edge of the Universe from which you surely must be able to look out. Try not to do that because that is not how things are.
Imagine you are in the actual glass structure of the bowl and not in the water, every direction you look is along the inside of the glass bowl. You then think to yourself 'i'll travel to the outside of the glass bowl and look outward'. When you get there and look you find you are still looking across the inside of the glass. No matter where you position yourself in the Universe it will always be the same - looking along on the inside of the bowl. A never ending inside skin of a fish bowl because the bowl is not round shaped.
Last edited by Quasar on Sat Jul 23, 2011 8:02 pm, edited 1 time in total.

David Frydman
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Post by David Frydman »

Mmmm!
David

Cliff
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Post by Cliff »

Dear Quasar
I think your "always looking inward idea about the nature of the Universe" is interesting.
However, I personally don't like your goldfish bowl analogy.
After reading your thoughts about it I find your goldfish bowl thoughts rather destroy your initial idea about always looking inward in the Universe - that's for me personally of course.
Even so an interesting thought - but I think forget the goldfish bowl as far as I'm concerned.
Best wishes from Cliff

Quasar
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Post by Quasar »

lol

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