Big Bang Theory

[Pilbara Pete (Peter)]

Hello to all,
Just a question that perplexes me and i wonder if anyone can shed some light (years). My question arises when astronomers say they can see so far with a telescope they can see a time just after the big bang. I understand that every light year you can see is a year into the past and if you are looking at something billions of light years away then the image is billions of years old but is our world/galaxy, our flesh and blood not a result of the big bang? So, we have travelled physically through space from the origin of the big bang since the big bang. In that case, how can light be just 'catching up' with us now? And, what direction are they looking in? It seems the big bang happened all around us and we are hurtling towards the centre of the universe, but thats another question - they don't end, do they?

[renormalised (Carl)]

The light that was in our part of the universe when the Big Bang occurred is still with us....as it is with everywhere else. It's the CMB, or Cosmic Microwave Background, the photons that have had their wavelengths stretched out so far that the background temperature of the universe is now 2.6K (or thereabouts). What they are saying is that the light that is coming from objects that were separated from our little corner of the universe by a certain distance, is only now coming into our view. So two points separated by a distance "x" in the early universe, during the Big Bang, were out of sight of one another because the horizon distance of our part of the universe at that stage was close by. Now, 13.7 billion years later, the light which was travelling from those objects to us is now within the horizon distance between the two sections of the universe (due to the expansion of the universe) and has allowed us to see those objects. That is, the horizon distance has increased with the expansion over time. You have to remember that this distance of 13.7 billion light years is only to do with the light travel time since those objects began to shine light towards us. Their actual physical distances from the Earth are considerably greater, due to the expansion. An object that is, say 12 billion light years from Earth, in terms of that light travel time, is some 25-30 billion light years away in actual physical distance. That's why you see quoted figures for the actual size of the universe (well, at least our section of it), in terms of its radius, as being around 45-47 billion light years. Here's a site you can goto which will help you to understand what I have just written...

http://www.astro.ucla.edu/~wright/cosmolog.htm

and more specifically...

http://www.astro.ucla.edu/~wright/cosmology_faq.html


Hope that helps

[Solanum]

And my simple understanding of it is firstly that the expansion is not from one point, so you can't think of a small sphere getting larger and that by looking backwards in time we are looking towards the 'origin'/middle. The expansion of the universe is in every direction, not just one, so we haven't travelled 'out' from a centre point, but simply apart. The classic example is to draw points on an uninflated balloon and then blow it up. Considering only the surface of the balloon, the points are now all further apart than they were, but haven't moved from a common origin.

Although we can see more and more of the universe as time goes on (in absolute volume terms) due to the time from the universe changing from being opaque to transparent being further away from the time of observation (i.e. the present), we see proportionally less and less of it as (in relative volume terms), because due to the expansion less and less of the light from the rest of the universe can 'catch up' with us due to light having a finite speed.

Anyone feel free to correct me if my simple interpretation is wrong!

[renormalised (Carl)]

Originally Posted by Solanum

And my simple understanding of it is firstly that the expansion is not from one point, so you can't think of a small sphere getting larger and that by looking backwards in time we are looking towards the 'origin'/middle. The expansion of the universe is in every direction, not just one, so we haven't travelled 'out' from a centre point, but simply apart. The classic example is to draw points on an uninflated balloon and then blow it up. Considering only the surface of the balloon, the points are now all further apart than they were, but haven't moved from a common origin.

Although we can see more and more of the universe as time goes on (in absolute volume terms) due to the time from the universe changing from being opaque to transparent being further away from the time of observation (i.e. the present), we see proportionally less and less of it as (in relative volume terms), because due to the expansion less and less of the light from the rest of the universe can 'catch up' with us due to light having a finite speed.

Anyone feel free to correct me if my simple interpretation is wrong!

The first part of what you wrote is correct. There is no centre to the Universe, as such. However, if you were talking about the centre of the expansion, you would have to move outside of spacetime to find it...i.e. you would have to jump to a higher dimensional state to view it. In effect you'd be placing yourself in superspace, or the space of all spaces. Which is, as far as supersymmetry is concerned, an 11 dimensional object.

The second part is a little harder. We do see more and more of the Universe over time, in terms of an increasing horizon distance bringing more of the Universe within the horizon. However, what we see is in effect a mirage, because those objects we see are only what we see of those objects as they were "x" billion years before. What they are now will be unknown as those objects now are much farther away from us than what they were then, and beyond the horizon limit. In effect we never catch up with those objects and by the time we did reach where they are "now", those objects would most likely no longer exist.

[Solanum]

Originally Posted by renormalised

Which is, as far as supersymmetry is concerned, an 11 dimensional object.

And some claim 20+ dimensions! It's going to be interesting to see if physics can come up with any evidence of all those rolled up little 'spaces'.

Originally Posted by renormalised

The second part is a little harder. We do see more and more of the Universe over time, in terms of an increasing horizon distance bringing more of the Universe within the horizon. However, what we see is in effect a mirage, because those objects we see are only what we see of those objects as they were "x" billion years before. What they are now will be unknown as those objects now are much farther away from us than what they were then, and beyond the horizon limit. In effect we never catch up with those objects and by the time we did reach where they are "now", those objects would most likely no longer exist.

Sure, like I said, it was a simple interpretation!

[renormalised (Carl)]

They only appear to be rolled up and small from the perspective of our own spacetime. In actual fact, they're much, much larger than our Universe. We're much like the surface of a bubble on the froth on a cappuccino. As they say about the Transformers....there's more than meets they eye

[Morepower (Craig)]

Personally I wouldn't be surprised to see the Big Bang Theory debunked in the near future. It seems scientists are clutching at straws. They say at an early point during the Big Bang it had to expand faster than the speed of light (expansion ?), just like that ! Even though for many years it was said nothing could exceed the speed of light, especially considering the amount of energy required to move matter near to the speed of light, let alone faster. And yet we still say nothing can go faster than light. And now again they say we have reached the limits of what we can see due to the fact that everything after a certain point is travelling faster than light. Not to mention when things don't seem to fit the model of the Big Bang they just keep adding Dimensions, first ~9, then 11, and now 20+ ? Then there is the before the Big Bang where there is a particle (?) that is infinitely smaller than an Atom and is infinitely dense and infinitely hot. I realise that it is just a "Theory", and I was an avid believer in it untill just recently. Now, for me at least, there are just too many holes and infinately's in it. BTW i'm not trying to start any arguments, however i am wondering if anyone else is questioning the Theory ? Apologies to the OP if I have thread jacked.

Respectfully
Craig

[Solanum]

Originally Posted by Morepower

They say at an early point during the Big Bang it had to expand faster than the speed of light (expansion ?), just like that !

Inflation, and actually there are quite a lot of observations that fit with it. I think many physicists thought it a kludge at first as well, but most have come round. I don't have the background to judge the validity of the evidence though!

I don't think the 'extra' dimensions are an inherent part of the big bang theory, they are one potential explanation for the properties of particles that we observe and also an explanation for the apparent appearance of the universe out of nothing. I also don't think any of the string or super symmetry theories are yet accepted by the majority as part of any 'standard model', but I may well be wrong in that.

I'm not sure anyone should be a 'believer' in anything, we can only go with the most plausible explanation that best fits our observations and allows testable predictions. One problem at the moment is that mathematical theory is well ahead of our ability to test it physically.

[sjastro]

Originally Posted by Morepower

Personally I wouldn't be surprised to see the Big Bang Theory debunked in the near future. It seems scientists are clutching at straws. They say at an early point during the Big Bang it had to expand faster than the speed of light (expansion ?), just like that ! Even though for many years it was said nothing could exceed the speed of light, especially considering the amount of energy required to move matter near to the speed of light, let alone faster. And yet we still say nothing can go faster than light. And now again they say we have reached the limits of what we can see due to the fact that everything after a certain point is travelling faster than light.

Hello Craig,

There is nothing contradictory about this.
An object moving in space-time cannot exceed the speed of light for the reasons you have given. Space-time expansion however can exceed the speed of light. It's important to realize that as space-time expands, objects in space-time do not change their spatial positions unless they are gravitationally influenced by other objects.

If the Universe in its very early history didn't expand faster than the speed of light then the Universe would violate causality (horizon problem).

Not to mention when things don't seem to fit the model of the Big Bang they just keep adding Dimensions, first ~9, then 11, and now 20+ ?

String theory uses Pure Mathematics, it is not a physical theory. The 10 or 26 dimensions has no relevance to physical cosmology.
Cosmologists are perfectly happy with their 4 dimensions.

There is also considerable debate in the physics community if String Theory is a scientific theory which is falsifiable or nothing more than an exercise in Philosophy which can neither be proven nor disproven.

Regards

Steven

[renormalised (Carl)]

Originally Posted by Morepower

Personally I wouldn't be surprised to see the Big Bang Theory debunked in the near future. It seems scientists are clutching at straws. They say at an early point during the Big Bang it had to expand faster than the speed of light (expansion ?), just like that ! Even though for many years it was said nothing could exceed the speed of light, especially considering the amount of energy required to move matter near to the speed of light, let alone faster. And yet we still say nothing can go faster than light. And now again they say we have reached the limits of what we can see due to the fact that everything after a certain point is travelling faster than light. Not to mention when things don't seem to fit the model of the Big Bang they just keep adding Dimensions, first ~9, then 11, and now 20+ ? Then there is the before the Big Bang where there is a particle (?) that is infinitely smaller than an Atom and is infinitely dense and infinitely hot. I realise that it is just a "Theory", and I was an avid believer in it untill just recently. Now, for me at least, there are just too many holes and infinately's in it. BTW i'm not trying to start any arguments, however i am wondering if anyone else is questioning the Theory ? Apologies to the OP if I have thread jacked.

Respectfully
Craig

Actually, SR doesn't say that nothing can travel faster than light. That is a great mistake that has been perpetrated by both laypeople and many scientists for many years. What Einstein said was this....no particle or object, other than light itself, can travel at the speed of light. The important bit to remember is that it is at the speed of light, that is the crucial piece of the statement. Due to the way objects (particles, planets, spaceships etc) behave and interact with the spacetime field which they occupy, they cannot be accelerated to the actual speed of light. This is because the energy required to do so is absurdly large, as close to infinity as you will get. It's only photons, which have their intrinsic properties of no rest mass or size, which can be made to move at light speed (they are, after all, particles of light!!!). All particles of light, regardless of their wavelengths, frequencies etc, move at the speed of light, in a vacuum. Unless, of course, they are slowed by some other agency...like glass, gas, water, gravity etc.

It may come as a surprise to many here (except those that have studied relativity at uni), that there are instances in which the equations for SR can only be applied to objects that always move at velocities faster than light!!!. These outcomes to the equations are valid answers, however, some of the characteristics of those answer would seem strange to us, such as "imaginary mass". But because things such as "imaginary mass" sound wacky, it doesn't mean it can't exist. There are stranger things in physics that are bandied about in labs and on blackboards that are being talked about every day.

As for spacetime itself tavelling fater than light, that is perfectly acceptable under SR (or GR for that matter). The speed of light limitation only applies to objects moving within and through spacetime itself. There's no speed limitation to spacetime's movements anywhere. It could expand at whatever velocity inflation imparted to it, and given what we observe, most likely did. What you have to remember is that spacetime itself is what was expanding. Not anything else or into a pre-existing space. Even given that it may have expanded out of a much larger multidimensional space, it still expanded into it's present state outside of that spacetime. Those other spacetime dimensions now appear to be miniscule to us, because of that shift in perspective caused by the expansion. It's hard to conceptualise for many, but that's what happened. In effect, the expansion due to inflation has cut us off from the other dimensions, except at the quantum level, where spacetime is most likely fluctuating randomly and chaotically....what they term the "spacetime froth".

Those increasing numbers of spacetime dimensions you mentioned....it depends on which equations of state for spacetime you use, the degrees of supersymmetry that are allowed for those equations, which determine how many spacetime dimensions there are. Some systems need upto 26 dimensions, most of them usually need 11, and it appears that given what we know of the numbers of fundamental particles and the interactions between them that this universe is composed of 11 dimensions overall.

Hope that helps with explaining things for you

[Morepower (Craig)]

Hi guys, and thanks for the replies, they have all been very helpful. Looks like I need to read up some on Space Time expansion. But what happens to the light that is being emitted from those objects that are travelling faster than it ? Won't we eventually see it ? Just like we eventually hear the sound from something travelling faster than sound ?

I may be confusing the "Theory of Everything" with "The Big Bang", however don't Cosmologists need some of these dimensions to explain the weakness of, or lack of Gravity after the "Super Force" was split ?

Many thanks
Craig

[renormalised (Carl)]

Any object that is beyond the horizon distance of the Local Universe will, by definition, be traveling faster than the speed of light w.r.t. our local reference frame. However, once enough time has passed and the horizon distance has increased in size, we will begin to see those objects as they were when they emitted the light coming to us at that particular point in time (when the horizon distance has reached them). Or, in reference to a ship traveling at warp speeds, you would see a mirage like effect where the light trailing the ship....effectively the ship's image....would eventually catch up to where the ship stopped. It would have to be slowed down, of course, as you wouldn't be able to see it otherwise. It would happen too quickly.

What they (cosmologists) are trying to say is that the reason why gravity is so weak compared to the other forces, is that most of its strength is being bled off into higher dimensional space. They theorise that it all depends on the geometry of cosmic strings w.r.t. to M-Brane Theory. If you consider that the universe we live in is the surface of a large, multidimensional object called a brane, then it's how the cosmic strings interact with the brane that determines whether gravity leaks away into the higher dimensions or is trapped within the brane itself. It depends on the geometry (shape) of the strings and how they attach themselves to the brane.

[Solanum]

Originally Posted by renormalised

What they (cosmologists) are trying to say is that the reason why gravity is so weak compared to the other forces, is that most of its strength is being bled off into higher dimensional space. They theorise that it all depends on the geometry of cosmic strings w.r.t. to M-Brane Theory. If you consider that the universe we live in is the surface of a large, multidimensional object called a brane, then it's how the cosmic strings interact with the brane that determines whether gravity leaks away into the higher dimensions or is trapped within the brane itself. It depends on the geometry (shape) of the strings and how they attach themselves to the brane.

And from memory, isn't the Higgs boson that the LHC is looking for supposed to be the particle associated (carrying the energy - whatever the proper term is!) with the brane on which we sit, so that if they find the Higg's Boson it will be a fair bit of evidence that all that stuff is correct? Carl?

[sjastro]

Originally Posted by renormalised

Any object that is beyond the horizon distance of the Local Universe will, by definition, be traveling faster than the speed of light w.r.t. our local reference frame. However, once enough time has passed and the horizon distance has increased in size, we will begin to see those objects as they were when they emitted the light coming to us at that particular point in time (when the horizon distance has reached them).

That would only be true if we lived in a matter dominated flat Universe where the Universe expands forever but at a decreasing rate until it reaches an asymtopic value.

Since the expansion of the Universe has been recently found to be accelerating the opposite is true. The Universe is becoming progressively more "unobservable" as more and more distant objects slip beyond the event horizon as the recession velocity of these objects due to space-time expansion exceeds the speed of light. Unless space-time expansion slows down these objects will never be observed again.

What they (cosmologists) are trying to say is that the reason why gravity is so weak compared to the other forces, is that most of its strength is being bled off into higher dimensional space. They theorise that it all depends on the geometry of cosmic strings w.r.t. to M-Brane Theory. If you consider that the universe we live in is the surface of a large, multidimensional object called a brane, then it's how the cosmic strings interact with the brane that determines whether gravity leaks away into the higher dimensions or is trapped within the brane itself. It depends on the geometry (shape) of the strings and how they attach themselves to the brane.

A fundamental problem with cosmological string theories is that multi-dimensional space is a solution for flat space-time.

One possibility of an accelerating universe is that space time rather than being flat has an open geometry. How do the cosmological string theories deal with this?

Regards

Steven

[renormalised (Carl)]

Originally Posted by sjastro

That would only be true if we lived in a matter dominated flat Universe where the Universe expands forever but at a decreasing rate until it reaches an asymtopic value.

Since the expansion of the Universe has been recently found to be accelerating the opposite is true. The Universe is becoming progressively more "unobservable" as more and more distant objects slip beyond the event horizon as the recession velocity of these objects due to space-time expansion exceeds the speed of light. Unless space-time expansion slows down these objects will never be observed again.



A fundamental problem with cosmological string theories is that multi-dimensional space is a solution for flat space-time.

One possibility of an accelerating universe is that space time rather than being flat has an open geometry. How do the cosmological string theories deal with this?

Regards

Steven

Yes that's correct, given that the universe appears to have an accelerating expansion, more and more of the Local Universe will slip over the event horizon and disappear off into the distance. But that is also predicated on the belief that this accelerated expansion is in fact a real phenomenon and not some illusion created by other factors, such as an imperfect understanding of supernova dynamics and evolution, unobserved dust and gas between the supernovae and ourselves, or some other effect we're as yet unaware of. Although, using Occam's Razor, it most likely going to be a real effect of expanding spacetime. So therefore what is being observed is real and means things are picking up pace.

It looks as though a theory of Quantum Gravity is needed to account for acceleration, if I understand what I'm reading. I haven't read up on this for quite awhile, so I'll have to acquaint myself with the latest literature. Here's a site to look at...

http://www.damtp.cam.ac.uk/user/gr/public/qg_qc.html

There's bucket loads of articles and sites to goto, so it'll take some time to absorb everything.

[renormalised (Carl)]

Originally Posted by Solanum

And from memory, isn't the Higgs boson that the LHC is looking for supposed to be the particle associated (carrying the energy - whatever the proper term is!) with the brane on which we sit, so that if they find the Higg's Boson it will be a fair bit of evidence that all that stuff is correct? Carl?

The Higgs boson is the particle which mediates mass....such that any other particle which interacts with the Higgs Field gains mass by the transfer of that property from the Higgs Field to the particle via the Higgs boson. And like all other particles, including the graviton (which they haven't found either, BTW) can be described as just another particular harmonic vibration of a string.

Have a look at this, it'll help you to understand it and suggest some further reading (which will be needed)....

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

[sjastro]

Originally Posted by Solanum

And from memory, isn't the Higgs boson that the LHC is looking for supposed to be the particle associated (carrying the energy - whatever the proper term is!) with the brane on which we sit, so that if they find the Higg's Boson it will be a fair bit of evidence that all that stuff is correct? Carl?

No it doesn't. It will confirm the Standard Model of Particle Physics.

The application of the Higgs field to cosmology (of which the Higgs boson is the QM particle of interaction) was one of the first applications of a scalar field to explain inflation. It wasn't very successful and has been replaced by more exotic scalar fields.

Regards

Steven

[renormalised (Carl)]

Originally Posted by sjastro

No it doesn't. It will confirm the Standard Model of Particle Physics.

The application of the Higgs field to cosmology (of which the Higgs boson is the QM particle of interaction) was one of the first applications of a scalar field to explain inflation. It wasn't very successful and has been replaced by more exotic scalar fields.

Regards

Steven

That's correct. Unless they don't find the Higgs and/or it turns out to not fit their predictions for what it's supposed to be. Or they may find something else entirely, who knows.

When is the LHC supposed to be back in full order and up and running??

[Jen]

Wow that was very well explained Carl
Thanks

[Morepower (Craig)]

Originally Posted by Jen

Wow that was very well explained Carl
Thanks

Yes agreed, and many thanks to all who replied. I love this stuff, it's just a shame I am unable to remember it all, and that some unfortunately goes over my head.

Craig