Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: chris on 04/07/2008 09:55:08
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The Universe is presumably expanding faster than the speed of light, but how, if light is the fastest thing that there is?
Chris
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Because it is the space itself that is expanding and not things that are moving quickly. On our scale this expansion is incredibly tiny and is completely unmeasureable.
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Wouldn't that be the same as if you flash 2 lasers in opposite directions, the distance between the photons would be expanding at twice the speed of light (relative to the observer in the middle of the lasers)
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Wouldn't that be the same as if you flash 2 lasers in opposite directions, the distance between the photons would be expanding at twice the speed of light (relative to the observer in the middle of the lasers)
But that quantity is not a physical velocity, just a mathematical one (it's not the same).
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Space has no mass so the expansion of it must be infinite.
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Chris - you really should do a search of the forum before you ask a question [:P]
This was asked very recently (http://www.thenakedscientists.com/forum/index.php?topic=15543.0)
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But if the red shift ratio is correct the outer part of the universe is expanding at speeds that exceed C
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Chris - you really should do a search of the forum before you ask a question [:P]
This was asked very recently (http://www.thenakedscientists.com/forum/index.php?topic=15543.0)
Sure Eth, I appreciate your attention to detail! However, the question is asked in a slightly different way and therefore useful to help people find the answer; your link to the other thread is extremely valuable in helping people to do this...
Cheers
Chris
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Putting the expansion of the universe into context
It is important always to remember that it is the space itself that is expanding and not things that are moving quickly. On our scale this expansion is incredibly tiny.
Let me do some simple calculations
The Hubble constant or expansion coefficient of our universe is about 70km/sec per megaparsec in astronomers units.
Let us now put it into more familiar units and relate it to distances in our solar system. A parsec is about 3.26 light years or 206,265 times the distace of the earth from the sun.
So over a distance of 206,265,000,000 the distace of the earth from the sun the expansion velocity is 70,000,000 millimeters per second (remember there are a million millimetres in a kilometer)
So the expansion of space between the earth and the sun is 70,000,000/206,265,000,000 millimetres per second.
This is about .00034 millimetres per second in about 150 million Km
let us give this velocity a bit longer to show itself, say one year
there are 365x24x60x60 = 31,536,000 seconds in a year
so in a year the space equal to the distace from the earth to the sun the space expands by 31,536,000x 0.00034 millimetres 10,722 mm or about 10 metres.
But surely I hear you say if the earth got ten metres further away from the sun every year over many millions of years this would have a significant effect? the answer is no! because the expansion of space does not significantly push the earth away from the sun because the energy of the attraction of gravity between the earth and the sun is so much greater that it completely overwhelms this effect and no change takes place.
It is only on the vast scales of distances between clusters of remote galaxies that the effect of the expansion of space can be measured. To measure it in the laboratory would be totally impossible.
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Chris,
The Universe is presumably expanding faster than the speed of light, but how, if light is the fastest thing that there is?
Chris
How about this answer from a puny mortal like me.
The universe "IS' expanding now at greater than light speed because it is embedded is "massless space" that has no speed limit.
Chris I know you posed this question because you know many people are puzzled by this. I know you knew the answer before you created the thread. You want to keep the forum fresh.
Regards
Alan