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Author Topic: Could there be objects so distant we do not know they're there?  (Read 2090 times)

Dave Overton

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Dave Overton asked the Naked Scientists:
   
Hi Chris,

My question is, we think we know the age of the universe because distant galaxies are fading out because of the doppler red shift by running it back to a singularity we calculate the age, but why cant there be objects many more times distant and we just don't know they're there?

Fantastic programme,

Dave Overton.

What do you think?


 

Offline lightarrow

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Dave Overton asked the Naked Scientists:
   
Hi Chris,

My question is, we think we know the age of the universe because distant galaxies are fading out because of the doppler red shift by running it back to a singularity we calculate the age, but why cant there be objects many more times distant and we just don't know they're there?

Fantastic programme,

Dave Overton.

What do you think?
We don't know what there is out of the visible universe, since light from those objects has not arrived to us yet:
http://en.wikipedia.org/wiki/Observable_universe
Quote
The comoving distance from Earth to the edge of the visible universe (also called particle horizon) is about 14 billion parsecs (46.5 billion light-years) in any direction.[2] This defines a lower limit on the comoving radius of the observable universe, although as noted in the introduction, it's expected that the visible universe is somewhat smaller than the observable universe since we only see light from the cosmic microwave background radiation that was emitted after the time of recombination, giving us the spherical surface of last scattering (gravitational waves could theoretically allow us to observe events that occurred earlier than the time of recombination, from regions of space outside this sphere). The visible universe is thus a sphere with a diameter of about 28 billion parsecs (about 93 billion light-years). Since space is roughly flat, this size corresponds to a comoving volume of about
(4/3)πR3 = 4 *1032 ly3

or about 3*1080 cubic meters.

The figures quoted above are distances now (in cosmological time), not distances at the time the light was emitted. For example, the cosmic microwave background radiation that we see right now was emitted at the time of recombination, 379,000[3] years after the Big Bang, which occurred around 13.7 billion years ago. This radiation was emitted by matter that has, in the intervening time, mostly condensed into galaxies, and those galaxies are now calculated to be about 46 billion light-years from us.
 

Offline yor_on

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Reading about this comoving idea got me rather confused, and still does in some ways.
"The age of the universe is about 13.7 billion years, but due to the expansion of space we are now observing objects that are now considerably farther away than a static 13.7 billion light-years distance. The edge of the observable universe is now located about 46.5 billion light-years away." says http://en.wikipedia.org/wiki/Observable_universe

If you're like me you wonder how they put forward their proof here. It seems that it builds on what is called Hubble’s Law. That law states that the redshift in light coming from distant galaxies is proportional to their distance. He noticed that the further away the galaxies was the faster they seemed to move away from us, that he built on the frequency's of the light coming from those distant objects, combined with a lot of different measuring methods, to make educated guesses about the possible distances of those galaxies he saw.

The rate with which they all seem to move away from us is called 'Hubble's constant'. One strange fact from his observations is that if this is correct, those galaxies far enough will move away from us faster than light. That can't be right, can it? The fastest speed possible is the speed of light in a vacuum, right. Ah, but that's where the expansion comes in.

You see, according to WMAP ( http://map.gsfc.nasa.gov/ ) that measures the cosmic microwave background radiation our universe underwent a period of accelerated expansion at its birth. That 'expansion' still takes place, and just like blowing up a balloon where upon you made dots, that expansion still separate all matter from each other according to this theory.

And just as with a black hole, one of the consequences of this idea is that there might be a part of spacetime 'traveling' faster than light, giving us a radius from where, outside of it, no light ever will be seen by us, called the Hubble radius. Just like a a black hole horizon it will keep its light. And an even more startling discovery if you combine the WMAP data with supernova observations, is that it seems that we still expands. And furthermore, this would then be the explanation why something can move faster than light. There is nothing 'moving' you see, it's only space 'expanding. So our galaxy is, if this is right, getting to get a lot 'lonelier' when searching for other 'visible' galaxies in the far future.

So is this true?
Don't know, it fits a lot of data, but it also build on a lot of assumptions.
One of the questions might be how we can observe the light from galaxies 46.5 billion light-years away. Now we could say that 'hey man, it's only space expanding, not matter' and then nod as if we had proved our point, but that wouldn't make me satisfied, and neither should it you. Even if that is correct that only space is so blessed we still have an awful lot of space in every atom, 99.99~ some percent. It could have to do with what we call the 'colour force' binding nucleus's and creating matter perhaps, or/and gravitation. There should be possible to do experiments on that.

But also one explanation why that very distant light could reach us would be those 'dots' constantly getting wider in our spacetime, due to our 'expansion'. But then it seems to me if we look at those photons as particles, shouldn't they become more dispersed distance wise from each other when this space ''grows'. Or if looking at it as waves, shouldn't they become even more 'redshifted'? As space'dot' 0 becomes space'dot 86 ( 85 new dots situated around 'dot' 0 :) through that expansion, sort of. That is, if believing that a wave have a spatial extension in space naturally. There is the alternative to see waves as something only existing at an interaction, and then that will be true if seen as particles also(photons).
« Last Edit: 14/02/2009 02:21:03 by yor_on »
 

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