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Science and Technology "Somewhere, something incredible is waiting to be known." - Carl Sagan.

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Old December 13 2012, 09:27 PM   #1
FluffyUnbound
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Question about how Hubble can see objects from soon after the Big Bang

So there's this article today that says:

The light we are seeing from them originated 380 million to 600 million years after the Big Bang, which cosmologists estimate happened 13.7 billion years ago.
I have never understood how this is mathematically possible.

The universe is expanding at less than the speed of light.

So 600 million years after the Big Bang, it should have been less than 600 million light years across.

So wouldn't the light emitted by these objects then have reached the limit of the universe not more than 1.2 billion years after it was emitted?

How can that light still be traveling around anywhere for us to see it?
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Old December 13 2012, 09:49 PM   #2
MacLeod
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Re: Question about how Hubble can see objects from soon after the Big

Remember Galaxies are moving as well. So as the universe expands the distance between galaxies can do so as well. So 12 billion or so years ago galaxy and galaxy B might have been sperated by a few hundred thousands light years. Whilst today they are sperated by billions of light years.
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Old December 13 2012, 09:54 PM   #3
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Re: Question about how Hubble can see objects from soon after the Big

First, the universe is not expanding at less than the speed of light, there are some stars presently moving away from us at a speed faster than the speed of light (these are all objects that are 14 billion light years away and further).

Second, the edge of the observable universe is 46 billion light years away.
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Old December 14 2012, 08:45 AM   #4
Asbo Zaprudder
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Re: Question about how Hubble can see objects from soon after the Big

It is mathematically possible, but you have to understand the maths. Even if you do understand the maths, it's difficult to get your head round. It's the space-time manifold that's expanding and the relative expansion is not limited to the speed of light. Weirdness ensues, for example non-conservation of energy.

http://math.ucr.edu/home/baez/physic...energy_gr.html

No-one knows how big the universe actually is, but measurements of its curvature seem to imply that it must be much bigger than its observable size.

http://atramateria.com/the-size-of-t...at-is-visible/

It might be infinite, or it might be finite but closed and not have an edge at all.

http://map.gsfc.nasa.gov/universe/uni_shape.html
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Old December 14 2012, 08:00 PM   #5
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Re: Question about how Hubble can see objects from soon after the Big

But if the space-time manifold is expanding at faster than the speed of light, then we shouldn't be able to see the rest of the universe outside of our galactic cluster at all.

Because the photons emitted from those light sources would end up acting like photons trying to escape from a black hole. Wouldn't they?

That's why I'm confused.

These distant objects are either moving away from us at less than / equal to the speed of light, or more than the speed of light. If it's the former, then the light should have passed our location already. If it's the latter, the light should never reach us and the universe should be a sort of reverse event horizon surrounding us in every direction.

Light that is 13 billion odd years old must have been 13 billion light years away from us when it was emitted, if c is a constant. Right?
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Old December 14 2012, 08:07 PM   #6
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Re: Question about how Hubble can see objects from soon after the Big

At first glance, as the Universe is 13.7 billion years old, it seems natural to think that any object at a greater distance than 13.7 billion light-years will not be visible. However, as the Universe is expanding, photons in the cosmic microwave background (the first light emitted) have traveled approximately 45 billion light-years to get there: this makes the observable Universe about 90 billion light-years across.
This is the part I can't get my head around.

But the cosmic background radiation bit has also never made sense to me. If these microwaves date to the time of the Big Bang, then they all originated at a single point and all were emitted within the same narrow window of time. So how can it be "background" radiation? Shouldn't it be a thin hollow globe of radiation, like a glass Christmas ornament but made of microwaves, the size of the universe and expanding at the speed of light? And with nothing behind it, since the emissions of the Bang stopped at some point? Wouldn't you need a continuous radiator to have the radiation be distributed evenly as a "background"?
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Old December 14 2012, 08:27 PM   #7
Asbo Zaprudder
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Re: Question about how Hubble can see objects from soon after the Big

FluffyUnbound wrote: View Post
But if the space-time manifold is expanding at faster than the speed of light, then we shouldn't be able to see the rest of the universe outside of our galactic cluster at all.

Because the photons emitted from those light sources would end up acting like photons trying to escape from a black hole. Wouldn't they?

That's why I'm confused.

These distant objects are either moving away from us at less than / equal to the speed of light, or more than the speed of light. If it's the former, then the light should have passed our location already. If it's the latter, the light should never reach us and the universe should be a sort of reverse event horizon surrounding us in every direction.

Light that is 13 billion odd years old must have been 13 billion light years away from us when it was emitted, if c is a constant. Right?
Only very widely separated points are beyond the observable horizon.

You'd think it's 13.7 billion light years to the horizon, but the space-time in between has expanded since the light was emitted, and the photons have lost energy as a result. In fact, depending on how you do the calculation, you can argue either that energy is lost or that it's been transformed.

ETA:
FluffyUnbound wrote: View Post
At first glance, as the Universe is 13.7 billion years old, it seems natural to think that any object at a greater distance than 13.7 billion light-years will not be visible. However, as the Universe is expanding, photons in the cosmic microwave background (the first light emitted) have traveled approximately 45 billion light-years to get there: this makes the observable Universe about 90 billion light-years across.
This is the part I can't get my head around.

But the cosmic background radiation bit has also never made sense to me. If these microwaves date to the time of the Big Bang, then they all originated at a single point and all were emitted within the same narrow window of time. So how can it be "background" radiation? Shouldn't it be a thin hollow globe of radiation, like a glass Christmas ornament but made of microwaves, the size of the universe and expanding at the speed of light? And with nothing behind it, since the emissions of the Bang stopped at some point? Wouldn't you need a continuous radiator to have the radiation be distributed evenly as a "background"?
The microwaves (actually redshifted from much higher energy photons) date from the recombination time just after the end of the radiation era - about 300,00 years after the BB.

http://library.thinkquest.org/C01266...tion%20era.htm

During the radiation era, the entire volume of the universe was dominated by radiation rather than by matter. So it was everywhere and not just a thin shell.

Last edited by Asbo Zaprudder; December 14 2012 at 09:26 PM.
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Old December 15 2012, 04:31 AM   #8
TheMasterOfOrion
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Re: Question about how Hubble can see objects from soon after the Big

One of the weirdest things in the early Universe is INFLATION, and if you come at it from a traditional newtonian and classical math background then this science behind it goes a little arsed ways.

and the physics and cosmology behind it is called the InflationaryUniverse model

We are now told that the very early Universe went through a quick period of rapid FTL expansion like a balloon blowing up faster than light speed.
But that's ok because none of the laws of physics and mathematics were broken in the real Universe, newton laws and einsteins theories and all those other nifty bits of math still hold true because the real Universe itself didn't expand.....you see the Real Universe is like the skin on an apple or the skin of a balloon and it expanded normal speed.....but that pocket of magicair inside we call inflation well that was allowed expand FTL because its only an expanding bubble of space-time
The Inflationary Expansion didn't last long though cos if it did our math of the stars would be a mess, so this expansion well it lasted less than a hundredth of a second, less than a microsecond, less than a nano second....about 10-^35 seconds.

In defense of the magic FTL Inflation theory
The science is actually pretty sound once the eggheads actually went out and tested it
The model helps explain why some of the Universe is now no longer observable, adds to the theory of missing observable matter and how space at the start didn't have initial curvature but the universe then started to warp and curve over time.
Laboratories like Fermilab and Cern are now finding some of the fundamental early particles that were expected to be found at the beginning of time in the Inflationary Model
NASA's Cobe satellite mission, the Hubble and Europe's Plank craft searched for predicted structures in the early universe, light red shifted into CMB radiation
and these structures scientists forecast in visible and microwave were consistent with satellite data
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