Ask Gugel Anything About the Big Bang

[Andy Ross]

[ QUOTE ]
I think that's why he used "horizon" in quotes. Is this
link pertinent?

http://en.wikipedia.org/wiki/Particle_horizon


[/ QUOTE ]
It doesn't matter what punctuation he surrounded horizon with. There is no cosmological horizon 14 billion light years away.

The link is pertinent. The value for conformal time is ~47 billion years. The particle horizon is 47 billion light years distant.

[ QUOTE ]
I agree there are some misconceptions as stated in the
"Misconceptions" section of the following link:

http://en.wikipedia.org/wiki/Observable_universe

[/ QUOTE ]

You can't be agreeing with me: I didn't say misconception. I said "completely wrong" and "rubbish". The 14 billion light year horizon is both.

[Gugel]

[ QUOTE ]
[ QUOTE ]
I think that's why he used "horizon" in quotes. Is this
link pertinent?

http://en.wikipedia.org/wiki/Particle_horizon


[/ QUOTE ]
It doesn't matter what punctuation he surrounded horizon with. There is no cosmological horizon 14 billion light years away.

The link is pertinent. The value for conformal time is ~47 billion years. The particle horizon is 47 billion light years distant.

[ QUOTE ]
I agree there are some misconceptions as stated in the
"Misconceptions" section of the following link:

http://en.wikipedia.org/wiki/Observable_universe

[/ QUOTE ]

You can't be agreeing with me: I didn't say misconception. I said "completely wrong" and "rubbish". The 14 billion light year horizon is both.

[/ QUOTE ]

This is getting a bit complicated, but it really depends on how you choose to measure distance (what coordinate system you choose).

The longest time a photon could have traveled is ~14 billion years (total distance = 14 billion light years). BUT, space is actually expanding. The road behind the photon actually got LONGER. The photon is still traveling at the speed of light, but it seemed to have covered more distance because new space was created behind it. In other words, when we look at that photon now, we see it covered 45 billion light years in only 14 billion years. The point is, you can say the "horizon" is 14 billion or 45 billion light years, depending on what you are measuring.

[Arp220]

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
I think that's why he used "horizon" in quotes. Is this
link pertinent?

http://en.wikipedia.org/wiki/Particle_horizon


[/ QUOTE ]
It doesn't matter what punctuation he surrounded horizon with. There is no cosmological horizon 14 billion light years away.

The link is pertinent. The value for conformal time is ~47 billion years. The particle horizon is 47 billion light years distant.

[ QUOTE ]
I agree there are some misconceptions as stated in the
"Misconceptions" section of the following link:

http://en.wikipedia.org/wiki/Observable_universe

[/ QUOTE ]

You can't be agreeing with me: I didn't say misconception. I said "completely wrong" and "rubbish". The 14 billion light year horizon is both.

[/ QUOTE ]

This is getting a bit complicated, but it really depends on how you choose to measure distance (what coordinate system you choose).

The longest time a photon could have traveled is ~14 billion years (total distance = 14 billion light years). BUT, space is actually expanding. The road behind the photon actually got LONGER. The photon is still traveling at the speed of light, but it seemed to have covered more distance because new space was created behind it. In other words, when we look at that photon now, we see it covered 45 billion light years in only 14 billion years. The point is, you can say the "horizon" is 14 billion or 45 billion light years, depending on what you are measuring.

[/ QUOTE ]

Oh for [censored] sake - THERE IS NO HORIZON OF ANY KIND 14 BILLION LIGHT YEARS AWAY!

14 billion light years, assuming we use this as a radial distance in comoving coordinates, corresponds to a redshift of about z=1.45. There is no 'horizon' of any sort at that redshift. The light travel time from this redshift is just over 9 billion years.

The majority of your post is reasonable, but it is factually incorrect to say that there is any kind of 'horizon' 14 billion light years away.

[Andy Ross]

[ QUOTE ]
This is getting a bit complicated, but it really depends on how you choose to measure distance (what coordinate system you choose).

The longest time a photon could have traveled is ~14 billion years (total distance = 14 billion light years). BUT, space is actually expanding. The road behind the photon actually got LONGER. The photon is still traveling at the speed of light, but it seemed to have covered more distance because new space was created behind it. In other words, when we look at that photon now, we see it covered 45 billion light years in only 14 billion years. The point is, you can say the "horizon" is 14 billion or 45 billion light years, depending on what you are measuring.

[/ QUOTE ]

The particle horizon is 47 billion light years away. We can see things further away than 14 billion light years (.... *most* of the universe we see is further away than that). You can say the horizon is whatever you like, but there isn't a meaningful horizon at 14 billion light years any more than there's one at the end of my nose.

Anyways, I'm off for the night.

In about 10^-43 seconds after the big bang began the universe began to cool and slowed it's expansion rate.

How did space expand so rapidly during this first period of time, when the laws of physics state that nothing can move faster than the speed of light.

I asked my teacher who gave me some BS that the laws of the universe weren't in affect then? pfft.

If this is so how can these be laws, and all that we would need to travel an obscene distance in a relatively short time would be to somehow recreate these same conditions.


Keep in Mind; Didn't read whole thread, These are juist random musings I had when I studued physics in high school.

[Andy Ross]

[ QUOTE ]
I asked my teacher who gave me some BS that the laws of the universe weren't in affect then? pfft.

[/ QUOTE ]

Hahaha, awesome stuff.

[ QUOTE ]
How did space expand so rapidly during this first period of time, when the laws of physics state that nothing can move faster than the speed of light.

[/ QUOTE ]

The short answer is that nothing has to move faster than the speed of light for space to expand so rapidly.

I think that the problem here is that everyone kind of "gets" special relativity. Nothing moves faster than light etc. The problem is that the intuition that worked well in special relativity hinders us when we look at the larger universe.

I hate these analogies (they never really work)... but think of expansion like this. You are standing on an elastic floor. You jump a metre forwards. Mid-jump, someone stretches the floor. A measuring tape shows that you jumped two metres across the floor. Let's say that it took you a second to make that jump: you didn't move at 2 m/s, but you are two metres from your start point.<font color="white">ugh</font>

When the farthest light started its journey, it was going to be a 14 billion light year journey to get here. As the light moved, the universe expanded, and the distance ended up being 47 billion light years. The light is from 47 billion light years away, but it only took 14 billion years to get here. There is no contradiction in that: nothing exceeded the speed of light. You can't multiply a cosmological time by the speed of light to give you the distance that light travelled. Neither can you divide a distance that light travelled by the cosmological time taken to give you the speed of light.

Galaxies can, and do, recede from us faster than the speed of light. The speed of photons towards us is the speed of light minus the recession velocity: c-v_rec. The Hubble Sphere is where the recessional velocity is the same as the speed of light. IF the Hubble Sphere were constant, a photon at this distance would stay there, and never approach us. Light inside would come nearer to us, and light outside would move away from us.

The Hubble Sphere isn't constant: it varies with time. There are galaxies which were outside the Hubble Sphere in the early universe. They were receding from us superluminally: the light emitted was moving away from us. Over time, the Hubble Sphere expanded, the light from those galaxies entered the HS and began to move towards us, eventually reaching us now. Therefore we can see galaxies that were, and are, receding faster than the speed of light. Again there's no problem with that. Nothing is "overtaking" photons, and the speed of light will locally be measured to be c everywhere.

[Bill Haywood]

[ QUOTE ]
the Big Bang did not start from a tiny point.

[/ QUOTE ]

So expansion was not propelled by anything like an explosion? It's all inflation of space? How about now -- are galaxies "moving" away from each other with velocity, or is it that more space is being created between us? And how in the hell do we tell the difference?

[ QUOTE ]
the observable universe extends about 47 billion light years in each direction, due to the metric expansion of space. This is basic cosmology.

[/ QUOTE ]

That's mighty obscure information to get all condescending about. The division of Korea was created in 1945 when junior US and Soviet officers picked a line on a map to define their occupation zones. This is basic history, didnja know?.

Nerd slugfest.

[Ohgod]

I agree it is slightly subtle - on the other hand, it IS basic information for someone setting themselves up as any kind of 'authority' on matters cosmological

[Bill Haywood]

Okay, new question about whether there is a center point to the universe. I understand the idea that space itself expands. The universe itself may be endless, but what about the matter originating in the BB? None if it is more than 14 billion or 47 billion apart. Or I guess that would be actually 94 BLY apart, if it's 47 in each direction. So within the infinite, shapeless universe, isn't there an expanding globe of stuff -- our observable universe -- that has a center point? If the universe is 94 billion LY wide, can't 47 BLY in from the frontier be considered a center point? And where in the sky would it be?


[ QUOTE ]
I agree it is slightly subtle - on the other hand, it IS basic information for someone setting themselves up as any kind of 'authority' on matters cosmological

[/ QUOTE ]

He understands that. The critics are just pouncing on something ambiguous, inadequately explained prose. It would be much more adult to say "Don't you mean 47 BLY?" rather than "gotcha, you wrong, wrong, wrong, bow before my superior intellect for all the world to see."

[twonine29]

How did anything ever come from nothing? If there was ever nothing...wouldn't there always be nothing????