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Offline DERYN

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In what direction is space expanding?
« on: 11/12/2010 16:29:12 »
Hi guys,  am I correct in saying that our universe is expanding outwards rather than inwards ?
And if so, is it expanding in any particular direction ? I'm thinking that if it was then could we determine exactly where the event known as the big bang originated ?

thanks, DERYN


 

Offline Bill S

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In what direction is space expanding?
« Reply #1 on: 13/12/2010 20:06:08 »
Hi, DERYN, as a non-scientist I am probably not the best one to try to answer this, but here are some thoughts, just to get the ball rolling.

Where did the BB happen?  The usual response to this in popular science books is to simply state that the Big Bang “happened everywhere”.  Perhaps this is an area in which the balloon analogy can help.  Imagine an un-inflated balloon on which you mark a small dot.  As you inflate the balloon, the dot grows.  Now, ask yourself where, within that enlarged patch, you might find your original mark.  Obviously, the answer must be “everywhere”.  The same can be said of the Big Bang.

Obviously your original dot has expanded , but has it spread across the balloon?  The answer has to be “no”, because the material of the balloon has expanded, carrying your mark with it.  It is tempting to think that your spot was made in the centre of the extended mark, but such is not strictly the case.

Of course, this does not really answer your question, except, perhaps, to say that the Universe is expanding “outward” from any internal point you care to select.
 

Offline JP

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In what direction is space expanding?
« Reply #2 on: 14/12/2010 07:27:10 »
Good analogy, Bill.  To push your example further, the big bang was supposed to be a singularity, i.e. everything was tightly packed, so imagine your uninflated balloon it just a tiny pinpoint and it inflates from there.  Which point on the balloon corresponds to that pinpoint?  All points on the balloon came from that pinpoint, so you can't really say where it started. 

I guess the scientific version of this would be that space and time as we know them started from a singularity at the big bang, so that asking "where in space did the big bang occur" doesn't make sense, since the big bang itself is the process that created space within our universe.
 

Offline peppercorn

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In what direction is space expanding?
« Reply #3 on: 14/12/2010 10:59:29 »
What has maybe been implied but not directly expressed about the balloon theory is it is a flat-worlders (2D observers) view of expansion.  In other words the surface (with no depth) of the balloon is where the observers 'live'.

The expansion happens everywhere, uniformly around the expanding surface, but the flat-worlders are always moving away from the start point along a (third) dimension they can not directly 'see'.

If I understand the model right are observed expansion is comparable but our 'surface' that we observe from is three dimensions not two.
 

Offline Bill S

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In what direction is space expanding?
« Reply #4 on: 14/12/2010 17:59:38 »
Perhaps the most difficult part to get one's head round is the idea that if you run the expansion backwards until you reach a ridiculously small point, you cannot say that that point is anywhere!
 

Offline DERYN

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In what direction is space expanding?
« Reply #5 on: 14/12/2010 20:54:54 »
Hi and thanks for the answers.

The 'balloon' certainly helped. An image in my head or a diagram speaks more than a thousand words to me. And it also helped because as a non scientist I have a totally non scientific way of looking at and thinking about things. For instance to me the 'big bang' happened at an exact point in time at a precise moment in time. Okay the precise moment can be calculated to a degree I think ? But an exact physical point/location as I have now discovered cannot be determined.

I also struggle with the fact that nothing can travel faster than light if anyone would like to provide me with an image or analogy to make it a bit clearer ?

thanks again,

Deryn (p.s. I realise my name in posts is in CAPITAL letters which doesn't look at all friendly,DERYN, sorry about that.)
 

Offline QuantumClue

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In what direction is space expanding?
« Reply #6 on: 15/12/2010 03:51:59 »
Hi guys,  am I correct in saying that our universe is expanding outwards rather than inwards ?
And if so, is it expanding in any particular direction ? I'm thinking that if it was then could we determine exactly where the event known as the big bang originated ?

thanks, DERYN


Forget the balloon analogy, as its not even a correct analogy. Most likely the universe doesn't even have a spherical shape at all, but has some geometry to it like a saddle, for a quick instance.

No, spacetime does not have a direction - space alone does not have a direction, nor does time. Space in our everyday lives appears to have a direction because the earth is a geometrical object with two poles. There is a bizarre consequence of quantum cosmology which states that universe is like a spherical object when mathematically viewed in imaginary time, but this is a more wierder consequence of the mathematics, and does us no goods to think of a universe in real time.

In real time, space does not have a direction, and the big bang happened everywhere on the spacetime map, meaning that the universe does not even contain a center to be moving from in any particular direction. Without a center, and with nothing existing outside the universe, how can anyone say that the universe is expanding anywhere? For it to be expanding to something, something must be sitting relative to the universe to make such a claim.
 

Offline JP

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In what direction is space expanding?
« Reply #7 on: 15/12/2010 07:39:15 »
Forget the balloon analogy, as its not even a correct analogy. Most likely the universe doesn't even have a spherical shape at all, but has some geometry to it like a saddle, for a quick instance.

I wouldn't go quite so far as to say forget it.  All lay-explanations of what is happening have issues, since they need to resort to 2D surfaces to describe the 3D universe.  This example gets at the idea that space itself is expanding without needing to have a "center," but obviously it isn't a rigorous mathematical model of the universe.

As far as I know, the best evidence shows that the universe is probably flat, but it's not conclusive.
 

Offline QuantumClue

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In what direction is space expanding?
« Reply #8 on: 15/12/2010 07:42:56 »
It seems quite conclusive. I see myself arguing with a lot of people here on this subject now.

With data being processed, all evidence seems to show our universe is almost flat. Now with the observable universe expanding faster than light, things truely are being panned out like flatbread. If also we are to believe we had an inflationary phase to the universe, this surely would have also flattened our early universe considerably.
 

Offline JP

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In what direction is space expanding?
« Reply #9 on: 15/12/2010 11:56:27 »
It seems quite conclusive. I see myself arguing with a lot of people here on this subject now.

With data being processed, all evidence seems to show our universe is almost flat. Now with the observable universe expanding faster than light, things truely are being panned out like flatbread. If also we are to believe we had an inflationary phase to the universe, this surely would have also flattened our early universe considerably.

It's conclusive that it's very close to flat, but very close to flat and perfectly flat are two different things.
 

Offline DERYN

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In what direction is space expanding?
« Reply #10 on: 15/12/2010 19:38:30 »
Quantum Clue,  you say the universe is expanding 'faster than light'. That relates to the rest of my question. Can in fact anything travel faster than light ?

Deryn
 

Offline imatfaal

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In what direction is space expanding?
« Reply #11 on: 16/12/2010 12:15:31 »
Deryn - nothing travels from point A to point B locally faster than the speed of light.  The universal expansion is a different concept - it is not that things are moving WITHIN SPACE, it is better to think that SPACE itself is getting bigger. 

As the latest example on this site of a very difficult concept:
- Write 1,2,3,4,5 in a row each along the length of an elastic band (these represent two galaxies)
- Stretch the elastic band
- You will notice that the 1 and 2 (2&3, 3&4 etc ie next to each other) move apart from each other
- But the distance increase between 1&2 is smaller than the distance increase between 1&3 and <1&4<1&5
- 1&5 are now a much longer way apart than before in the same time as 1&2 moved less far apart
- relative to each other 1&5 travelled faster than 2&3; in general the further apart they are to start with the further they travel when the band is stretched
- Space is expanding (like the elastic band was stretching) - some galaxies are so far apart that like 1&5 the distance increase is huge, bigger than light could bridge, but like the numbers on the elastic band  in local space they are not really moving at all.

The elastic band was only expanding in one dimension - space is doing it in 3 (I think only three).  You could thing of the surface of a balloon as a 2D exampled and the raisins in a cake for 3D. 

 As a numerical example of this expansion of space - galaxies that emitted light 13 billion years ago (which has just reached us) are not 13 billion light years away (that would be too easy) - in fact they are over 40 billion light years away.  the light has travelled 13 billion light years distance, but space itself has expanded more than twice that much since the light set out.  Its all mind-boggling - but I hope this has helped 
 

Offline DERYN

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In what direction is space expanding?
« Reply #12 on: 16/12/2010 19:26:47 »
Well done, I totally got the elastic band bit. The current cake image was brilliant ! My expanding universe will forever resemble a cooking bara brith !

many thanks,

Deryn
 

Offline QuantumClue

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In what direction is space expanding?
« Reply #13 on: 17/12/2010 13:03:19 »
Quantum Clue,  you say the universe is expanding 'faster than light'. That relates to the rest of my question. Can in fact anything travel faster than light ?

Deryn

When I say the universe is expanded, one must not think that kinetically objects are moving at this speed enclosed within the universe. They are moving faster than light relative to us because the vacuum literally ''drags'' matter at this speed, and so does not violate relativity.
 

Offline Bill S

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In what direction is space expanding?
« Reply #14 on: 17/12/2010 18:03:50 »
Quote
Can in fact anything travel faster than light?

Would I be right in thinking that relativity does not forbid FTL travel, only acceleration from sub-luminal to super-luminal speeds? 
 

Offline QuantumClue

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In what direction is space expanding?
« Reply #15 on: 17/12/2010 18:25:57 »
Well, it has to do with a relativistic link between a gravitational mass and inertial mass. Things which contain matter cannot exceed lightspeed because it would require more energy in the observable universe. Accelerating matter to this speed therefore, is in fact impossible.

Subluminal, which we call particles as Bradyons, are particles which travel less than luminal speeds (lightspeed). Particles already travelling at this speed are called luxons, such as gluons, photons and even the unseen higgs boson.
 

Offline Bill S

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« Reply #16 on: 17/12/2010 22:45:55 »
If the tachyon exists, it spends its time travelling at above light speed.  Right?  I assume there is no physical evidence for its existence, though.
 

Offline QuantumClue

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In what direction is space expanding?
« Reply #17 on: 17/12/2010 22:58:52 »
If the tachyon exists, it would be a particle with negative matter, and one which exists for a superluminal speed, as you well know. What you might not know is that the tachyon exhibits an infinite energy at it's lowest energy, the speed of light. When we usually think of lowest of energies, we never tend to think about speeds of light, when we usually attribute it to lots of energy in the energy-mass equivalance principle. At it's lowest speed, it cannot go any lower because it needs an infinite amount of mass to do so.

This is how relativity enters and allows tachyonic matter. Tachyonic matter never existed at speeds lower than lightspeed, nor any which existed for the speed of light itself. These particles would begin their lifetime with an infinite amount of speed, oscillating through time, but at the same time, could never be observed.
 

Offline QuantumClue

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In what direction is space expanding?
« Reply #18 on: 17/12/2010 23:00:17 »
But also, I forgot to mention, tachyon condensate exists, which rules out their existences mathematically, so they are certain mathematically never to be found.
 

Offline Bill S

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In what direction is space expanding?
« Reply #19 on: 18/12/2010 15:34:37 »
Quote from: QC
I forgot to mention, tachyon condensate exists

What's a tachyon condensate, and why does its existence preclude the existence of tachyons?  (Mathematically, of course, but please try to keep any maths in the answer as simple as possible. ???
 

Offline QuantumClue

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Offline Bill S

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In what direction is space expanding?
« Reply #21 on: 18/12/2010 21:44:16 »
Thanks! ??? ;D
 

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In what direction is space expanding?
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