Universe expansion.

stoneill

Here's one I've been pondering about for a while.
As you look out into the universe, the endless expanse dotted with stars from our own galaxy, and further, distant galaxies, regressing faster and faster with the expanding universe the further away they are.
All matter, all energy was contained within the singularity that was at the creation of the universe.
From the exact moment of the big bang the universe expanded - was this expansion faster than the speed of light?

rccaulfield

stoneill wrote: »

Here's one I've been pondering about for a while.
As you look out into the universe, the endless expanse dotted with stars from our own galaxy, and further, distant galaxies, regressing faster and faster with the expanding universe the further away they are.
All matter, all energy was contained within the singularity that was at the creation of the universe.
From the exact moment of the big bang the universe expanded - was this expansion faster than the speed of light?

Yep much faster! There was no light at that time according to the standard model so no laws broken.

Humans eh!

rccaulfield wrote: »

Yep much faster! There was no light at that time according to the standard model so no laws broken.

Good answer.

Its believed that it was vacuum energy that drove the expansion. Alan Guth reckoned that this expansion or inflation into vacuum occurred in the first 1034 seconds of its existence when the fledgling universe expanded, doubling in size 85 or 90 times in that time. Whether matter can exceed lightspeed under these exceptional circumstances is open to debate.

As rccaulfield says there were no laws or anything else in existence at the time so literally the universe was creating its own limitations.
The laws of physics are determined by how objects react and are limited by their environment and other existing forces ie gravity etc. In the absence of forces and environment at the beginning of the universe, anything is possible.

stoneill

So, it is at this first few femtoseconds that current physics does not work, and this why there is no unified theory of everything?

slade_x

stoneill wrote: »

So, it is at this first few femtoseconds that current physics does not work, and this why there is no unified theory of everything?

According to the theory current physics didnt exist, they had not yet evolved. it was only from further expansion and cooling, as primordial particles eventualy evolved/ decayed into somewhat stable states that allowed current elementary particles and forces to exist and eventualy form particles like hydrogen that the universe we see now could exist, a balance between mass, energy and gravity.
There is no unified theory because the mathematical physics of the macroworld doesnt exactly correspond for all with what we observe below the microworld to put it simply.
Quantum mechanics tries to observe these fundementals but observations on that level are difficult and dont behave in an objectively observable state enough to explain their erratic behaviour (seemingly shooting in and out of existance and of course quantum entanglement)
The original idea for some was to regard electrons paths around a nucleus in much the same way planets orbit stars and to observe protons and neutrons behaviour in a nucleus in a similar regard but such isnt the case

The Shroedingers cat thought experiment introduces the quantum entaglement paradox if you're not already familiar:
http://en.wikipedia.org/wiki/Schr%C3%B6dinger's_cat

There wont be a unified theory until whatever force / particle or otherwise was responsible for creating gravity and giving particles their mass can be quantified (temporarily smashed back into existance like experiments currently underway at the LHC which is basically about uncovering the evolution of particles and mass) understanding what gravity is and how it came to be is key.

The big bang theory, while infered from the observable expansion of the universe doesnt really explain what forces or state was at play at the beginning if there was a beginning of our universe. The basic idea was since we observe the universe is expanding in all directions it can be infered that if you rewind events everything could have come from a single point. The implementation of the idea of a singularity doesnt come with an explanation; much like beyond the event horizon of black holes. it just leads to more and more questions.

There are alternative theories of course like string theory etc. but a true understanding unfortunately is currently incomplete.

Cú Giobach

stoneill wrote: »

Here's one I've been pondering about for a while.
As you look out into the universe, the endless expanse dotted with stars from our own galaxy, and further, distant galaxies, regressing faster and faster with the expanding universe the further away they are.
All matter, all energy was contained within the singularity that was at the creation of the universe.
From the exact moment of the big bang the universe expanded - was this expansion faster than the speed of light?

The speed of light limit is for things moving through space, no law is broken by space itself expanding faster than light, two widely separated galaxies/objects could be receding from each other faster than light due to universal expansion because neither of them would actually be moving through space.

maguffin

Cú Giobach wrote: »

The speed of light limit is for things moving through space, no law is broken by space itself expanding faster than light, two widely separated galaxies/objects could be receding from each other faster than light due to universal expansion because neither of them would actually be moving through space.

Is there observable/scientific proof that 'space' is actually expanding?? I thought that it was accepted that 'space' is infinite (since its boundaries cannot be observed or measured) and that the observable 'universe', ie. All stellar matter (created in the big bang) is expanding into it.

Just a thought!

maguffin

Rubecula

maguffin wrote: »

Is there observable/scientific proof that 'space' is actually expanding?? I thought that it was accepted that 'space' is infinite (since its boundaries cannot be observed or measured) and that the observable 'universe', ie. All stellar matter (created in the big bang) is expanding into it.

Just a thought!

maguffin

We have to rely on mathematical equations for many things in support of theories. I am not much of a mathematician myself so I stand to be corrected. However according to current theory, based on Einstein's E=MC2, space did not exist before the start of the universe, nor did time. Matter only came into existance some period after the start.

RichieC

love this guy

https://www.youtube.com/watch?v=myjaVI7_6Is

stoneill

Nice video -

So what I get from this is that z=1.4 equals galaxies moving at speed of light.
(In relativistic terms - they are located at part of space-time that is moving at the speed of light)
at z>1.4 then the object is moving away from us greater that speed of light and it is the expansion of space-time that red shifts light, not the apparent motion of the source of light.
Space-time was explained to me like the skin of a balloon, each point stretching away from each other point as it inflates.
However, observing marshmallow in a microwave oven could be a better analogy as that expands in all directions!

AugustusMinimus

maguffin wrote: »

Is there observable/scientific proof that 'space' is actually expanding?? I thought that it was accepted that 'space' is infinite (since its boundaries cannot be observed or measured) and that the observable 'universe', ie. All stellar matter (created in the big bang) is expanding into it.

Just a thought!

maguffin

It is likely that space itself is not infinite. If this was true then the big bang couldn't have created the universe, it could only have created the matter and energy in it.

The universe in simple terms is 4 dimensional. Height, width, length and time. The universe is theorised to have many shapes. The easiest to think of is a hypersphere. It's impossible to imagine this as your brain can't comprehend 4 dimensional objects.

So think of it like this. Just think that the world is flat. There is length and width, but no height.

In this universe, if space was infinite, it would be like a flat sheet of paper which goes on for ever in all directions, with people living on it. However, to compare this flat universe to our own, you'd have to grab the edges of this sheet of paper and make it into the shape of a sphere.

Think about it. The people living on it wouldn't have a clue that their universe is actually in the shape of a ball. If they walked far enough in their universe, they'd eventually return to where they started.

This is what our universe is like, except we have an extra dimension. Our universe is not infinite. If you start out in one direction, if you keep going, you'll eventually come back to where you started.

Now. How is the universe expanding. Back to our flat world. We claim that our world is in the shape of a sphere. For this world to be expanding, it would be like a baloon being blown up. As it gets blown up, the space in this universe gets bigger and bigger and everything moves further and further apart.

You may ask along what dimension is the universe expanding. Well, it's expanding along the time dimension. The same is happening in this universe. It is expanding along the 4th dimension (time).

There are a lot of theories of what causes time to move forward. By far the easiest, is that as the universe is expanding, the 3 normal dimension we perceive, are moving through the 4th dimension due to the initial shove by the big bang.

Time travel in this setup may also be possible. If you go back to our flat world. There should be an infinite amount of universes within our paper ball like a russian doll. These universes represent the past. There would be onces outside of our paper ball too which would represent the future.

keithoq

I'm fascinated by this topic. Really well explained. I always imagined the universe to be spherical, like a balloon, and we are inside it. Taking into account the time dimension, it's actually just unfathomable.
:eek:

AugustusMinimus wrote: »

It is likely that space itself is not infinite. If this was true then the big bang couldn't have created the universe, it could only have created the matter and energy in it.

The universe in simple terms is 4 dimensional. Height, width, length and time. The universe is theorised to have many shapes. The easiest to think of is a hypersphere. It's impossible to imagine this as your brain can't comprehend 4 dimensional objects.

So think of it like this. Just think that the world is flat. There is length and width, but no height.

In this universe, if space was infinite, it would be like a flat sheet of paper which goes on for ever in all directions, with people living on it. However, to compare this flat universe to our own, you'd have to grab the edges of this sheet of paper and make it into the shape of a sphere.

Think about it. The people living on it wouldn't have a clue that their universe is actually in the shape of a ball. If they walked far enough in their universe, they'd eventually return to where they started.

This is what our universe is like, except we have an extra dimension. Our universe is not infinite. If you start out in one direction, if you keep going, you'll eventually come back to where you started.

Now. How is the universe expanding. Back to our flat world. We claim that our world is in the shape of a sphere. For this world to be expanding, it would be like a baloon being blown up. As it gets blown up, the space in this universe gets bigger and bigger and everything moves further and further apart.

You may ask along what dimension is the universe expanding. Well, it's expanding along the time dimension. The same is happening in this universe. It is expanding along the 4th dimension (time).

There are a lot of theories of what causes time to move forward. By far the easiest, is that as the universe is expanding, the 3 normal dimension we perceive, are moving through the 4th dimension due to the initial shove by the big bang.

Time travel in this setup may also be possible. If you go back to our flat world. There should be an infinite amount of universes within our paper ball like a russian doll. These universes represent the past. There would be onces outside of our paper ball too which would represent the future.

AugustusMinimus

keithoq wrote: »

I'm fascinated by this topic. Really well explained. I always imagined the universe to be spherical, like a balloon, and we are inside it. Taking into account the time dimension, it's actually just unfathomable.
:eek:

We actually live on the surface of a 4 dimensional universe.

The surface itself actually has 3 dimension which is what we expierience as the world around us. It's impossible for us to imagine this though.

Bruthal

stoneill wrote: »

As you look out into the universe, the endless expanse dotted with stars from our own galaxy, and further, distant galaxies, regressing faster and faster with the expanding universe the further away they are.

When anything expands, the further any 2 points are apart, the faster they will move away from each other. For example, 12 cars start in the centre of a circle, and all drive away in straight lines from the centre at 100kph. Any car will see that the farther they are from any given car they observe, the faster they are actually seperating from that car.

AugustusMinimus

robbie7730 wrote: »

When anything expands, the further any 2 points are apart, the faster they will move away from each other. For example, 12 cars start in the centre of a circle, and all drive away in straight lines from the centre at 100kph. Any car will see that the farther they are from any given car they observe, the faster they are actually seperating from that car.

I think the easiest example is that of an accordian.

When any accordian is pulled apart, if you take two points on each end, they are seperating apart faster than two points nearer to the middle of the accordian.

Bruthal

AugustusMinimus wrote: »

I think the easiest example is that of an accordian.

When any accordian is pulled apart, if you take two points on each end, they are seperating apart faster than two points nearer to the middle of the accordian.

I would of thought the big bang resulted in everything moving from a common point, like an explosion. And in an explosion, all the particles moving apart will observe any others at a higher velocity the farther away they are from the observing particle.

AugustusMinimus

robbie7730 wrote: »

I would of thought the big bang resulted in everything moving from a common point, like an explosion. And in an explosion, all the particles moving apart will observe any others at a higher velocity the farther away they are from the observing particle.

The big bang did start at a point. However, that point doesn't exit in the present. It only exists in the past. There is no place in our universe presently where the big bang happened.

Picture a 2 dimensional universe. Flat people are living on the surface of a ball. They have no idea they are living on a ball as they can't look up. To them it looks flat. Their universe is also finite in size. The surface of the ball is their entire universe. Their universe also has no edge.

Now, in such a universe, guess where the big bang happened ? Well, it would have happen inside the ball right at the centre. If their universe is expanding, the ball would be inflating. This would give the impression to them that every single thing in their universe is moving away from each other.

The universe would be expanding along the time dimension. They expierence the ball inflating in two ways.

1. Their universe is getting bigger.
2. Time is moving forward as their two dimensional "surface of the ball" is moving along the x axis.

What is inside the ball is the past (hence the big bang is in the past and the spatial dimension does not exist anymore).

For our universe you must add a 3rd spacial dimension. This is obviously impossible to think about. Similarly, our universe is expanding. But there is no centre of our universe and all the galaxies are all moving away from each other uniformly.

Back to the baloon. Points further away from each other on the baloon will move away from each other faster when the baloon is blown up compared to points closer together. This is because there is less space inbetween them to expand.

In linear motion, two cars driving away from each other (for instance) will be driving away from each other at the same rate, no matter what distance they are apart.

(A long post I know. This stuff is really hard to express in writing).

Amtmann

There is a good podcast from Astronomycast.com dealing with this topic at the following addresses:

What is the shape of the universe?

How big is the universe?

EDIT: Can't get the links to work; they're episodes 78 and 79 respectively.

AugustusMinimus

I scrapped my last post. I realised that the growth of the circumference of the universe would indeed be linear in relation to the growth of it's radius.

However, this would not be the case if the universe was 5 dimensional and was expanding along 2 axis.

AugustusMinimus

Tremelo wrote: »

There is a good podcast from Astronomycast.com dealing with this topic at the following addresses:

What is the shape of the universe?

How big is the universe?

EDIT: Can't get the links to work; they're episodes 78 and 79 respectively.

Two of the main theories is that it's either a 4d sphere or a 4d torus (donut).

For some reason, the 4d torus just doesn't seem eloquent enough for me. It would also require the place where the big bang to have happened to now not be within the 4d universe at all. I dunno if this is even possible.

Arpa

I remember seeing this programme with Alan Davies,

http://www.youtube.com/watch?v=6cu4_Vd6TTw

where Marcus du Sautoy uses the Grande Arche in Paris,

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

to explain the 4 dimensional nature of the Universe.

Really interesting stuff and helps put it in context perfectly.

Part 3/6 is where he discusses the 4 dimensional cube.