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Faster than light

ZOG

By ZOG
in The Astro Lounge

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ZOG

ZOG

Posted
Posted

I was watching a program on tv last week, it may have been one of the universe series. Anyhow, the presenter was saying that we will never know the size of the universe because, as it is expanding faster and faster, the outer galaxies will eventually attain faster than light speed and we will never see the light from them. In other words they will just drop off the radar.

Einsteins theory is that the whole universe is governed by the speed of light and nothing can travel any faster. So what will happen ? will these outer galaxies attain light speed and go no faster, or, if they do surpass the speed of light, will it throw all our current laws of physics into turmoil.

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kniclander

kniclander

Posted
Posted

apparently, the expansion of the universe is not limited by the rule that nothing can travel faster than light. don't ask me why:icon_scratch:. I am sure that someone who knows more than me (ie almost anyone) will come along to confuse you further :D

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Shibby

Shibby

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While I don't pretend to fully understand the subject, I can at least point you in the right direction - this is known as the universal event horizon. The distance at which objects are so far away that the light from them has never had enough time to reach us (as the universe is 14bn years old). As space itself expands, galaxies reach these great distances without necessarily having to travel through space. The size of the true universe is unknown, it could be many many times larger than the observable universe, but apparently, I've just learnt, it could also be smaller!

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themos

themos

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also whats it expanding into???

A pound today buys you fewer Mars bars than it did 20 years ago.

A sphere of radius one-billion-light-years today catches fewer galaxies than it did ten billion years ago.

Nothing has to expand into something else for this to happen.

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Shibby

Shibby

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Mars bar analogy - I like it :D

The only way I can get my head around it is, you have to think of the "3D" universe as if it were the (flat) surface of a balloon. As the balloon expands, the galaxies move away from one another, but the universe is still continuous - it "wraps around" on itself.

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CaptPaul

CaptPaul

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so i think ive prob go this completley wrong but do you mean expanding is actually meaning the light is finally reaching us now and we are seeing things that "wernt there" before because the light had not reached us???

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themos

themos

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so i think ive prob go this completley wrong but do you mean expanding is actually meaning the light is finally reaching us now and we are seeing things that "wernt there" before because the light had not reached us???

Seeing things today that we couldn't see yesterday happens in lots of scenarios, irrespective of the expansion. It just depends on the fact that the galaxies haven't been around for ever but were actually created at some time and light has only had so much time to get here.

Expansion (or inflation) of the universe affects how this plays out. If there's too little expansion then there's no limit to what we will be able to see. If there's more, then there may be a maximum of stuff we will ever see. If there's too much, then we might eventually lose sight of all other galaxies.

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Earl

Earl

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From what understand the big bang was everywhere at once and expansion is everywhere.

Its so easy to think of thnigs haveing a start point but in this case everywhere is the start point.

maybe :D

also. i wonder if.

two beams of light fired from a point in oposite directions, are they not traveling faster than the speed of light away from each other?

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CaptPaul

CaptPaul

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Thanks theres some great explanations on here i think a few people need carears as physics teachers!.

I think im gonna stick to looking and just wandering in a wow kind of way. space is a very beautiful place and theres no need to explain that one!

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themos

themos

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are they not traveling faster than the speed of light away from each other?

Apparently not. The "law of addition of velocities" is simply false, it doesn't hold in nature. But it kind of does when the velocities involved are tiny (compared to the speed of light).

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gary1968

gary1968

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Having read through all of this my head now hurts..... :p

But one of my life long questions is this, if a car is travelling at light speed and I were to switch the head lights on would the light get out of the reflector? and if it did would it not be travelling fastrer than light?:D

Gary

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Mr Spock

Mr Spock

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It doesn't matter how fast a galaxy is moving away from us, the light reaching us still appears to us to be travelling at the speed of light which is constant. It's all 'relative' :D

Of course it would be red-shifted so far we would need long wavelength equipment to detect it.

But, is the galaxy moving away from us, or are we moving away from it?

There we go again, us humans assuming we are the centre of the universe... :p

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Shibby

Shibby

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But one of my life long questions is this, if a car is travelling at light speed and I were to switch the head lights on would the light get out of the reflector?

This was one of Einstein's life long questions too - which led him to the answer - no - and the theory of special relativity, in fact the very definition of it.

Although by 'travelling at the speed of light', if you mean relative to an observer, then this is not possible. (other than for electromagnetic radiation e.g. light). But special relativity applies to all relative speeds up to the speed of light.

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themos

themos

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A car cannot travel at light speed with respect to anything.

You might think that it can do so with respect to light itself. But light does not have a "rest frame" and so that measurement of speed cannot be done.

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themos

themos

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At whatever speed the car is going with respect to any other material observer ("rest frame"), the light will appear to leave the reflector at light speed in the ordinary way. The driver will not be able to compute any kind of absolute speed by observing how the light is emitted.

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Earl

Earl

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But, is the galaxy moving away from us, or are we moving away from it?

There we go again, us humans assuming we are the centre of the universe... :D

Or are they stationary and the space expands?

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