for the physicists...

bluechair84

I watched an episode of Horizon recently that blew my mind... It described the size of the universe. In doing so, it defined for me 'the visible universe' which says that we can only see as far as light has had time to travel. If the universe was born 8 Billion years ago, we can only see the distance light has travelled in 8 billion years. They demonstrated this with a view of the universe showing a bubble of what we could see from the oldest light in all directions. Now... if that bubble represents the distance light can travel in the time the universe has existed, how can it be any bigger than that if the speed of light is a universal speed restriction? Surely the edge of the universe couldn't have at one point (or even still presently) been travelling faster than the speed of light for there to be anything further than 8 Billion light years? I would assume maximum radius would be 8 Billion light years, but more likely far less...

And if you can solve that, maybe you can also explain why I'm able to get toothpaste out of a tube my girlfriend gave up on a week ago? Answers to the crudcatcher I think!

Chunkers1980

Hawkins explains it on Discovery with a train. But it hurt my head.

jndb72

Read a few of his (Hawkins) books a while back. Found them very disappointing, mainly because I found him very patronising.

kieranb

well, I think you are coming at it from the wrong angle. when they say the universe is expanding they don't mean that within a vast space things are moving apart like a fragments froma bomb blast, what is actually happening is that the space itself is getting bigger, like dots on the surface of a balloon. as you inflate the dots become further apart although the dots aren't moving of their own accord?

bluechair84

But the edge of space itself would have to be moving faster then the speed of light to have gotten away from 'the visible universe' boundary?
And things are always explained better though use of childhood toys. My preference would be lego if anyone can give that kind of analogy!

pilch

Chunkers1980 wrote:

Hawkins explains it on Discovery with a train. But it hurt my head.

I saw some of that programme... I had the same reaction

bennett_346

bluechair84 wrote:

But the edge of space itself would have to be moving faster then the speed of light to have gotten away from 'the visible universe' boundary?
And things are always explained better though use of childhood toys. My preference would be lego if anyone can give that kind of analogy!

No. Imagine the light comes from the edge of the universe and arrives here for us to see 8 billion years later. During that time the universe expands and we are too young to see the next amount of light arrive back here (the light that comes from the new edge).

cooldad

It's all a conspiracy - there are no stars. It's all done with lightbulbs and a bloody big black sheet.

cooldad

Bugger I thought this was Crudcatcher.

bennett_346

cooldad wrote:

a bloody big black sheet.

I laid one of those before.

bluechair84

bennett_346 wrote:

bluechair84 wrote:

But the edge of space itself would have to be moving faster then the speed of light to have gotten away from 'the visible universe' boundary?
And things are always explained better though use of childhood toys. My preference would be lego if anyone can give that kind of analogy!

No. Imagine the light comes from the edge of the universe and arrives here for us to see 8 billion years later. During that time the universe expands and we are too young to see the next amount of light arrive back here (the light that comes from the new edge).

Ahrum... I think that makes some sense.

Daz555

error

Daz555

bluechair84 wrote:

bennett_346 wrote:

bluechair84 wrote:

But the edge of space itself would have to be moving faster then the speed of light to have gotten away from 'the visible universe' boundary?
And things are always explained better though use of childhood toys. My preference would be lego if anyone can give that kind of analogy!

No. Imagine the light comes from the edge of the universe and arrives here for us to see 8 billion years later. During that time the universe expands and we are too young to see the next amount of light arrive back here (the light that comes from the new edge).

Ahrum... I think that makes some sense.

No - it really really does not make any sense at all. That there is no edge to the universe means the explanation given is not helpful I'm afraid. There is also no centre to the universe. There is a common misconception that the universe exploded from the the big bang at a certain "central" point in the universe. From this misconception it is easy to make some assumptions about our universe which are entirely false.

Big Bang by Simon Singh is a great book for the intelligent layman - read it, it is superb.

In the mean time, this wiki article will help:

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

Make sure you at least branch out and read a few of the linked pages as well - cosmic microwave background radiation is very important for example.

There is also a good section on common misconceptions.

bluechair84

Daz555 wrote:

In the mean time, this wiki article will help:

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

A little bit of my brain just dribbled out of my nose. But I am genuinely interested so I'll look up the book.

Daz555

On the subject of why there is no edge to the universe (or centre), the balloon analogy helps.

Imagine that your are 2-dimensional being who lives in the surface of a balloon - the material of the balloon represents space and the air inside and outside is not part of this analogy.

As a 2D being you can only move forwards/back/left/right and up/down do not exist for you. As you move around and study your "universe" you will find that it has no edge - you can travel around your universe forever and will return to your originating point if you travel far enough. If you are a 2D chap who dabbles in science you may also have figured out that your space is curved.

The balloon analogy also helps with the idea of the way in which the universe expands for our mythical 2D being. When you inflate the ballon it is space itself which expands, rather than objects flying away 'into" some void or other.

As 3D beings it is hard to scale this idea up in our minds to our own unviverse but we do indeed know that spacetime is curved.

kieranb

so, if you're a bit religious, think of it as God blowing up a balloon in a higher dimensional space and we all live on the surface. So obviously the big bang is that first big puff when one starts blowing up a balloon and as the balloon gets bigger the rate of inflation (on the surface of the balloon) slows as the volume and the surface area is increasing but the amount of puff per breath remains the same.

pilch

kieranb wrote:

so, if you're a bit religious, think of it as God blowing up a balloon in a higher dimensional space and we all live on the surface. So obviously the big bang is that first big puff when one starts blowing up a balloon and as the balloon gets bigger the rate of inflation (on the surface of the balloon) slows as the volume and the surface area is increasing but the amount of puff per breath remains the same.

But according to Hawkins, time didn't exist before the big bang, therefore there was no 'time' for god or a creator to exist, therefore there is no god...

cooldad

pilch wrote:

kieranb wrote:

so, if you're a bit religious, think of it as God blowing up a balloon in a higher dimensional space and we all live on the surface. So obviously the big bang is that first big puff when one starts blowing up a balloon and as the balloon gets bigger the rate of inflation (on the surface of the balloon) slows as the volume and the surface area is increasing but the amount of puff per breath remains the same.

But according to Hawkins, time didn't exist before the big bang, therefore there was no 'time' for god or a creator to exist, therefore there is no god...

Maybe Hawkins is god, just not letting on - would ruin his rep for god to talk through a computer.

bluechair84

The religulous argument that I'm aware of is that God creates the universe in a manner he sees fit, and if he wants it to appear as if he doesn't exist, then that's what we have; a Universe with no experimental or visible signs of his presense. This way, faith can be tested. Which is a stunning argument in both it's ridiculousness and it's simplicity. Hitchens vs Hitchens debat on youtube is fantstic for a creationist vs scientific argument.

mrmonkfinger

bluechair84 wrote:

a Universe with no experimental or visible signs of his presense

No observable or experimentally provable signs of "his presence" means you could never know if "God" was ever the right concept, or even the concept of the universe being deliberately created in any way, which just goes to prove that any religion is a pointless construct of our collective imagination.

mrmonkfinger

cooldad wrote:

Maybe Hawkins is god, just not letting on - would ruin his rep for god to talk through a computer.

Or maybe God just really liked Intergalactic by the Beastie Boys and thought it would be cool if he sounded a bit like that.

bluechair84

mrmonkfinger wrote:

bluechair84 wrote:

a Universe with no experimental or visible signs of his presense

No observable or experimentally provable signs of "his presence" means you could never know if "God" was ever the right concept, or even the concept of the universe being deliberately created in any way, which just goes to prove that any religion is a pointless construct of our collective imagination.

Well I completely agree. My very good friend goes along with this argument; that you can't disprove 'his' omnipotence when he designed it to appear as if he isn't here. Other than the fact that this is proof of every conceivable wack-theory going, and our greatest asset as humans is that of reason which is the only thing that we can rely on...

kieranb

why would one believe and worship should a god? Anyway if you're going to go around believing things with no supporting evidence why not make up something a bit better? Like the vikings did with Valhalla?

mrmonkfinger

bluechair84 wrote:

Well I completely agree. My very good friend goes along with this argument; that you can't disprove 'his' omnipotence when he designed it to appear as if he isn't here. Other than the fact that this is proof of every conceivable wack-theory going, and our greatest asset as humans is that of reason which is the only thing that we can rely on...

Yep. That's "burdon of proof":

https://s3.amazonaws.com/yourlogicalfal ... hic_A1.pdf

Reason, humankind's greatest asset? I would say so.

bluechair84

cyd190468 wrote:

And beyond that it says you can't travel through space at a velocity greater than c. It doesn't limit the rate at which space can expand.

This is quite interesting. So the universe's expansion is exempt from [the law that sets speed of light as the speed limit]

supersonic

Velocity in co-moving coordinates ;-).

bluechair84

I knew it was as simple as that

Daz555

bluechair84 wrote:

cyd190468 wrote:

And beyond that it says you can't travel through space at a velocity greater than c. It doesn't limit the rate at which space can expand.

This is quite interesting. So the universe's expansion is exempt from [the law that sets speed of light as the speed limit]

Not really exempt - it is all relative! Different elements of the universe can be moving away from each other at a speed which is greater than the speed of light in respect to each other. We can for example see galaxies moving away from us at a speed greater than the speed of light (red shifted to a high degree) but this does not mean the galaxy itself is traveling faster than the speed of light - both are moving away from each other at sub light speed.