Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 05/02/2015 00:30:01
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Steve Tate asked the Naked Scientists:
If we can see billions of years into the past towards the beginning of time (big bang). And, if all matter/energy in the observable universe was in one place (the singularity) at that point. Then, how did we get to where we are faster than the light we are seeing now?
Also, if space is expanding then is matter/energy also expanding at the same rate?
Also, if space is expanding why is the speed of light not getting quicker? Is light actually slowing down, relatively speaking?
What do you think?
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Steve Tate asked the Naked Scientists:
how did we get to where we are faster than the light we are seeing now?
What do you think?
We didn't. Imagine you and a friend on a salt flat. You get in your cars and drive at say 90° Until you are a mile apart. Your friend then fires a gun (blank of course) and you see a delay between smoke and bang. However, you have never driven greater than the speed of sound!
I will leave the questions about space and matter expanding to deeper thinks than wot I am.
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If we can see billions of years into the past towards the beginning of time (big bang). And, if all matter/energy in the observable universe was in one place (the singularity) at that point. Then, how did we get to where we are faster than the light we are seeing now?
Compound interest! The universe is thought to have been expanding for 13.8 billion years, but the observable universe has a radius of 46 billion light years. That's because space expands, and then there's more space, so then there's more expansion. Cosmologist Neil Cornish talked about it here (http://edition.cnn.com/2004/TECH/space/05/24/universe.wide/), where he was suggesting the actual universe has a diameter of 78 billion light years or more. You can get a handle on this with a compound interest calculator (http://www.thecalculatorsite.com/finance/calculators/compoundinterestcalculator.php). Start with $1, use an interest rate of 36.51% for 14 years compounded yearly, and you end up with $78.
1 $1.37
2 $1.86
3 $2.54
4 $3.47
5 $4.74
6 $6.47
7 $8.83
8 $12.06
9 $16.46
10 $22.47
11 $30.68
12 $41.88
13 $57.17
14 $78.04
Think of this as a universe that was 1 billion light years in radius increasing by 36.51% every billion years.
Also, if space is expanding then is matter/energy also expanding at the same rate?
Matter isn't expanding. It's like the raisin cake analogy (http://www.ucolick.org/~max/Astro18_2010/Lectures/Lecture%202%20Our%20Place%20in%20the%20Universe/raisin_cake.htm). Space expands, galaxies are gravitationally bound, they don't expand. Nor do atoms etc because they're electromagnetically bound.
Also, if space is expanding why is the speed of light not getting quicker?
I think it is actually. You tend not to hear much about this, but it bubbles up now and then. Here's (http://www.newscientist.com/article/dn6092-speed-of-light-may-have-changed-recently.html#.VNP0d9JybIU) something from about ten years back. But note the article gets it wrong by saying "a varying speed of light contradicts Einstein's theory of relativity". It doesn't. See this:
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.thenakedscientists.com%2Fforum%2Findex.php%3Faction%3Ddlattach%3Btopic%3D54160.0%3Battach%3D19455%3Bimage&hash=996897d8b077cbd11f692c13ad526541)
Is light actually slowing down, relatively speaking?
No. Jo Magueijo and others proposed this (http://en.wikipedia.org/wiki/Variable_speed_of_light#Modern_VSL_theories_as_an_alternative_to_cosmic_inflation) proposed this, but IMHO they got it back to front. The "coordinate" speed of light decreases in line with gravitational potential, which is inversely related to spatial energy density. For light to slow down the spatial energy density in the universe at large would have to be increasing. Conservation of energy says it can't be. Conservation of energy says the spatial energy density ought to be decreasing. Which would mean the speed of light ought to be increasing.
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For your first question, it's about your preferences (presumptions). You can define it that way, but it won't fit a inflation, more or less a Victorian view of the world to me. Better to wonder how a 'space' come to exist, what is needed for it to be defined, and (very important) from 'where' you can define it.
The second one is a question about conservation laws. They exist, and they seem to work. So there the question becomes why they work, if a inflation exist. Two ways I see, one is the one in where you assume a Victorian way of looking at it, defining the universe as some 'expanding sphere'. Then it's about energy, and it has to be 'lent' from somewhere else inside this 'universal sphere'. Or it is about a symmetry break growing, and then you need to look at the first question, deciding how you want to treat it.
The last one is simple, it's the speed of communication, information, and the 'speed' of your local arrow.