how did we get so far away from the big bang

MooseJam

They say the universe is 14 billion years old as this is how far back we can see, however how did we get to be so far away from the beginning ? I don't know how fast our galaxy is moving away from the beginning but it's not at the speed of light nor anything close to it so how did we manage to get 14 billion light years away ? Also if we can look 14 billion years back to the early days of the universe wouldn't there be a mirror image out the other side so in fact the universe would be 28 billion light years across ?

Kevster

The conjectured and accepted figure is 13.7 billion years. With modern telescopic equipment we can see back roughly 12 billion years. However, as instruments improve, we are increasingly becoming able to see galaxies further and further back in time. Keep in mind that the the first stars started forming 1 billion years after the Big Bang, however. That technically means we should be able to see back a maximum of 12.7 billion years.

Before that time, the only 'visible' radiation is that of the Cosmic Microwave Background, which set-off on it's path 400,000 years after the big bang.


You are right about the Universe being 28 billion (well, 27.4 billion) light-years across. That equates to roughly 150 billion trillion (150,000,000,000,000,000,000,000 miles) miles. What do you mean by a 'mirror image' though? There is no mirror image at all.


... ...I'm not 100% sure on any of this by the way! Maybe someone that's more sure will reply. I keep reading conflicting reports about how far back we can actually see.

MooseJam

yeah mirror image is bad phrasing, the way I see it and I'm probably totally wrong is the universe is like a beach ball and we are near the surface of the beach ball and as we look back in time towards the big bang we are looking into the center of the beach ball, so right at the very center of the beach ball 13.7 billion light years away is the big bang, and if you continue through the center the universe continues on out the other side another 13.7 billion years ?

I don't understand how we managed to get 13.7 billion light years away from the big bang in 13.7 billion years, it would seem to imply we have been moving at the speed of light and this is impossible ?

mathias

Instead of a Beach ball think of a Bowling Ball , or any solid ball.

Now imagine that expanding to is current size from say a pinhead ( for arguments sake ).

We are not on the surface of the ball we are somewhere between it and the centre , due to expansion , the objects further away ( closer to the surface ) are travelling faster ( or at least appear to be ) than the objects closer to the center , we would be somewhere in between.

So we are not necessarily 13.7 billion years away from the big bang. We can see twelve , but I dont think we know our exact position relative to the center !

Maybe Im wrong?

Kevster

Yes, that analogy is a good one matthias.

We know how old the Universe is (13.7 billion years) but we do not actually know how far the 'view' horizon is. What is certain is that we are definately NOT at the edge of the Universe; we are somewhere in between it and the origin of the Big Bang. Our current view horizon is roughly 12 billion light-years but some scientists have conjectured that the actual horizon is as far away as 20 billion light-years.

I don't understand how we managed to get 13.7 billion light years away from the big bang in 13.7 billion years, it would seem to imply we have been moving at the speed of light and this is impossible ?

We're not that far from the Big Bang at all. We simply worked-out that the Universe is 13.7 billion years old by examining the red-shift of the Cosmic Micowave Background. We don't actually know where the origin of the Big Bang was so we can't measure distance.

MooseJam

Kevster wrote:

We're not that far from the Big Bang at all. We simply worked-out that the Universe is 13.7 billion years old by examining the red-shift of the Cosmic Micowave Background. We don't actually know where the origin of the Big Bang was so we can't measure distance.

but we can currently look back 12 billion years and believe there is another billion years beyond that so thats 13 billion light years distant, if the big bang took place 13.7 billion years ago and sent us hurtling off into space we have travelled 13 billion light years in 13.7 billion years which I would have thought would be impossible

Kevster

You've got me there... ...

Grayarea

MooseJam wrote:

but we can currently look back 12 billion years and believe there is another billion years beyond that so thats 13 billion light years distant, if the big bang took place 13.7 billion years ago and sent us hurtling off into space we have travelled 13 billion light years in 13.7 billion years which I would have thought would be impossible

I don't believe anyone is saying that we have traveled 13 billion light years since the big bang. As Kevster points out we don't know what our position is relative the the big bang and that question in general may not be easy to answer or relevant.

The main issue with the ball analogy that has been used is the thought that you look to the balls center to see the site of the big bang. This is in fact wrong and very misleading. As we look in any direction we are looking backwards in time. The Cosmic Background Radiation that is the earliest elements of the universe after the big bang are in fact visible in all directions from earth.

When I get home tomorrow night I will post a ISBN for a good book on this subject.

Later,

Gray

Son Goku

We never moved away from the spot where the Big Bang happened because the Big Bang happened everywhere at once, we're still there. There's no such thing as a position relative to the Big Bang.

Our galaxy originated from small bump in the early universe, with other bumps nearby. However as time went on more and more distance was created between the galaxies, not because they were moving away from each other, but because the universe was literally increasing the scale of space in between them. The galaxy has never truly "moved" from where it started off, in a sense.

MooseJam

Grayarea wrote:

I don't believe anyone is saying that we have traveled 13 billion light years since the big bang. As Kevster points out we don't know what our position is relative the the big bang and that question in general may not be easy to answer or relevant.

I'm saying it
We can currently look back 12.7 billion light years, we are looking back to the big bang when we do this so thats at least 12.7 billion light years we have travelled if we started out at the big bang

Grayarea wrote:

The main issue with the ball analogy that has been used is the thought that you look to the balls center to see the site of the big bang. This is in fact wrong and very misleading. As we look in any direction we are looking backwards in time. The Cosmic Background Radiation that is the earliest elements of the universe after the big bang are in fact visible in all directions from earth.

Sure as we look in any direction we are looking back in time, but isn't there only one direction that looks back to the big bang, I'm imagining the big bang to just be like any explosion here on earth where there would be an epicenter and you can look towards it

Son Goku

MooseJam wrote:

Sure as we look in any direction we are looking back in time, but isn't there only one direction that looks back to the big bang, I'm imagining the big bang to just be like any explosion here on earth where there would be an epicenter and you can look towards it

Everywhere looks toward it and everywhere is the epicenter.

MooseJam

Son Goku wrote:

Everywhere looks toward it and everywhere is the epicenter.

wow thats mind bending, well then my thinking is way off then, I would have thought theres only one direction, I shall have to read up on this stuff it's very interesting

MooseJam

If anyone can suggest a good book explaining the universe I'd be very gratefull

Grayarea

As promised;

Brain Greene

The Fabric of the Cosmos

ISBN 0-141-0111-4

It's very good and easy to understand.

Later,

Gray

MooseJam

many thanks

Kevster

I've heard of this book and I can even picture the cover of it. I think I'll snap it up too. It's about time I bought another book because all I have at present are Hawking's books.

Calibos

The baloon analogy is a good one. Imagine the surface of a baloon is a 2 dimensional representation of the universe. Our Galaxy is a dot on the surface of this half inflated baloon. Mark another dot an inch or two away from the first to represent another galaxy a billion light years away. Blow up the baloon. The Galaxy dots haven't moved from their positions on the baloon but the are get farther apart as you blow up the baloon because the space in between is expanding. Mark a few more dots. From the perspective of any one of those dots, all the other dots are moving away from it. So no matter where you are all the other galaxies appear to be moving away from you in every direction. Hey!! YOU are the centre of the universe.....in a manner of speaking.

Kevster

Yes, and that's why the early Universe was much more active than it is now; and, thus, why we generally only find quasars and other forms of Active Galactic Nucleii when we tune our 'scopes to look back billions of years. Matter is just continually drifting further and further apart and even collisions between galaxies are rare now.

However - and I was surprised by this - the milky way is currently shredding apart a small galaxy in Saggitarius and, in a few billion years, we'll collide with Andromeda.

Mahatma coat

Kevster wrote:

Yes, and that's why the early Universe was much more active than it is now; and, thus, why we generally only find quasars and other forms of Active Galactic Nucleii when we tune our 'scopes to look back billions of years. Matter is just continually drifting further and further apart and even collisions between galaxies are rare now.

However - and I was surprised by this - the milky way is currently shredding apart a small galaxy in Saggitarius and, in a few billion years, we'll collide with Andromeda.

ben with the discussion up to here, like the baloon analogy, but the thing that I dont get is that if the universis expanding, therefore creating greater distances between galaxies, how the feck are they managing to collide all over the shop???

Somnus

This stuff is amazing!

Where can i get that book Grayarea? I'd love to learn about this

AlmightyCushion

Son Goku wrote:

Everywhere looks toward it and everywhere is the epicenter.

My first time on this forum and I've only been here 5 minutes and my head already hurts. Cool stuff though.

Son Goku

Mahatma coat wrote:

ben with the discussion up to here, like the baloon analogy, but the thing that I dont get is that if the universis expanding, therefore creating greater distances between galaxies, how the feck are they managing to collide all over the shop???

The gravity of a group of galaxies tends to over power the expansion effect from the rest of the universe. Really the expansion is creating greater distances between galactic groups.

Mahatma coat

Ah, ok thats a reasonable explanation

nacho libre

AlmightyCushion wrote:

My first time on this forum and I've only been here 5 minutes and my head already hurts. Cool stuff though.

haha. i've been on it a couple of times before but i have the same feeling reading this thread.

That book mentioned earlier seems like a good introduction to start learning about this subject.

AlmightyCushion

nacho libre wrote:

haha. i've been on it a couple of times before but i have the same feeling reading this thread.

That book mentioned earlier seems like a good introduction to start learning about this subject.

I must take a look at it. I've seen a couple of horizon documentaries which are kinda like a dummies guide. They generally only cover one topic though.

Tzetze

MooseJam wrote:

They say the universe is 14 billion years old as this is how far back we can see, however how did we get to be so far away from the beginning ? I don't know how fast our galaxy is moving away from the beginning but it's not at the speed of light nor anything close to it so how did we manage to get 14 billion light years away ? Also if we can look 14 billion years back to the early days of the universe wouldn't there be a mirror image out the other side so in fact the universe would be 28 billion light years across ?

Is the universe expanding faster than the speed of light?

(This interpretation assumes that the Hubble "constant" actually stays constant over those million years, which it doesn't, but given that a million years is extremely short on cosmic timescales, this is a pretty good approximation. It also assumes that when we talk about the "distance" between two galaxies, we are referring to the distance between them right now -- that is, the distance we would measure if we somehow "pressed the freeze-frame button" on the universe, thereby stopping the expansion, and then extended a really long tape measure between the two galaxies and read off the distance. There are many other distances that can be defined in cosmology, but this is the most useful one for the current question.)

If we use the definition of distance given above (and only if we use this definition and no other), then the Hubble constant tells us that for every megaparsec of distance between two galaxies, the apparent speed at which the galaxies move apart from each other is greater by 71 kilometers per second. Since we know that the speed of light is around 300,000 kilometers per second, it is easy to calculate how far away two galaxies must be in order to be moving away from each other faster than the speed of light. The answer we get is that the two galaxies must be separated by around 4,200 megaparsecs (130,000,000,000,000,000,000,000 kilometers)...I found that if you use a value of around 1.4 for z (the redshift), you get the required distance of 4,200 megaparsecs. Therefore, any galaxy with a redshift greater than 1.4 is currently moving away from us faster than the speed of light.

Can we see these galaxies? Yes, we certainly can!..

Remember that, although these galaxies are approaching the threshold where their light being emitted won't outrun the rate of expansion of the space between us, it will take billions of years for it to be perceptable to us. When that does happen, they will appear to freeze and fade away completely (except for the local group).

MooseJam

I always thought the idea that the universe was expanding was due to galaxies moving away from the big bang, like shrapnel from an explosion, and not that space itself was expanding like dough in an oven, I'm sure I'll never understand how the nothingness of space expands

nacho libre

speaking of the speed of light.


http://www.telegraph.co.uk/earth/main.jhtml?xml=/earth/2007/08/16/scispeed116.xml

MooseJam

I would have thought that would make headline news everywhere. mind you searching on google for speed of light broken bring up numerous reports of different scientists having broken it, in this one they say 300 times faster than the speed of light - warp speed ahead
http://www.science-spirit.org/archive_cm_detail.php?new_id=305