[Rubinelli, Peter M]

Rubinelli, Peter M  asked the Naked Scientists:
   
Hello,
� 
My name is Peter Rubinelli.

I would like to know why the big bang model is favoured over the steady state model for explaining the expansion of the universe.

What is the evidence that leads to the big bang as the favoured model?
� 
Thank you. I really enjoy your show.
 
 
Peter M. Rubinelli, Ph.D.
Purdue University
USA

What do you think?

[graham.d]

It fits with a lot of observation - particularly Hubble expansion and the microwave background. The Bondi, Hoyle et al Steady State theory made valiant attempts to stave off defeat but became more or less untenable after the microwave background data was produced.

[Farsight]

I think there's also evidence in fundamental physics, epitomized by Einstein's stress-energy tensor. Stress is akin to pressure, and things under pressure tend to expand. We can see this in the Casimir effect, wherein space demonstrates an innate pressure.

The issue is that if the universe was in a steady state, there would have to be something to stop the galaxies moving together due to gravity. Einstein introduced his lambda (Λ) term for this, see http://en.wikipedia.org/wiki/Cosmological_constant. The problem isn't with Λ per se, it's making it exactly counteract gravity to maintain the steady state. I don't know how he missed the "pressure" expansion aspect, and I guess it's why he later said it was his greatest blunder. He could have predicted the expansion of the universe before Hubble spotted the redshift, see http://en.wikipedia.org/wiki/Edwin_Hubble.

As an aside, I read a really interesting article recently called Dark Energy: back to Newton? which suggests that Newton had a lambda term. See http://www.thenakedscientists.com/forum/index.php?topic=28014.msg294505

But having said all that, there are people who don't agree with me. See for example http://www.hiltonratcliffe.com/. Hilton describes himself as a "heretic" and advocates a steady-state universe. He's more cosmologist than fundamental physicist, but it's only fair that I mention the counter-argument.

[PhysBang]

OK, there are a number of misconceptions here.

But before getting to that, it's worth noting that the Steady State theory has been out of favour for decades. Even those who promoted the Steady State theory switched to different theories by the 1990s.

Simply put, there is too much evidence for significant change in the nature of the universe over its observable history.

I think there's also evidence in fundamental physics, epitomized by Einstein's stress-energy tensor. Stress is akin to pressure, and things under pressure tend to expand. We can see this in the Casimir effect, wherein space demonstrates an innate pressure.

First, stress and pressure are two very different things in physics.

Second, while the Casimir effect might be a measure of the pressure of empty space, it is not necessarily one that influences the overall expansion of the universe. To date, no scientists has made a convincing argument linking the Casimir effect to cosmological expansion, primarily because there are not measurable comparisons between the two.

Third, the Steady State theory incorporated expansion, and it even incorporated a form of dark energy. As dark energy is what one often attempts to associate with the Casimir effect, the Casimir effect cannot be thought to be something that speaks against the Steady State theory.

The issue is that if the universe was in a steady state, there would have to be something to stop the galaxies moving together due to gravity. Einstein introduced his lambda (Λ) term for this, see http://en.wikipedia.org/wiki/Cosmological_constant. The problem isn't with Λ per se, it's making it exactly counteract gravity to maintain the steady state. I don't know how he missed the "pressure" expansion aspect, and I guess it's why he later said it was his greatest blunder. He could have predicted the expansion of the universe before Hubble spotted the redshift, see http://en.wikipedia.org/wiki/Edwin_Hubble.

Gamow claimed that Einstein called the cosmological constant a blunder, but there is no other source for this quote. Einstein did speak vehemently against the constant following 1929, though.

And, again, the steady state of the steady state theory does not mean that there is no expansion. Standard steady state theory had expansion, with the density of the universe being "filled in", so to speak, by the creation of matter and energy from a field that took the place of the cosmological constant.

As an aside, I read a really interesting article recently called Dark Energy: back to Newton? which suggests that Newton had a lambda term. See http://www.thenakedscientists.com/forum/index.php?topic=28014.msg294505

It is misleading to say that Newton had anything like a dark energy term. The authors of that article went too far in trying to sell their position to a popular science audience. Most of the article is good, and actually makes clear that what Newton examined (and correctly rejected) is only superficially like dark energy.

[yor_on]

There is no pressure that I know of to a 'free vacuum'?
If you are of the view of photons, or waves, traveling in space ala Feynman's 'many paths' you would have a radiative pressure, but then you would have to ask yourself how it introduces itself when there is no matter interacting?
outer Space
Problems with the 'steady state'

[LeeE]

An expanding universe cannot, by definition, be a steady state universe.

[PhysBang]

An expanding universe cannot, by definition, be a steady state universe.

Well, everyone who ever proposed a steady state universe disagrees with you.

[LeeE]

Umm... do you want to think that through again?

[PhysBang]

No.

The steady state theory proposed that the universe always looked the same, including the expansion that we have seen since 1929. To account for this, the steady state theories proposed a field that created matter so that the average density of the universe remained the same. This means that the universe can always expand and always look about the same.

[JP]

There is no pressure that I know of to a 'free vacuum'?
If you are of the view of photons, or waves, traveling in space ala Feynman's 'many paths' you would have a radiative pressure, but then you would have to ask yourself how it introduces itself when there is no matter interacting?
outer Space
Problems with the 'steady state'

There is in theory pressure in a vacuum.  It comes from the idea of empty space as having a bunch of virtual photons popping into and out of existence.  If you put two conducting plates close together, you can exclude some of those photons from the region between the plates.  Since you have more possible photons outside than inside, they exert a net pressure on the plates, which is the Casimir effect. I think another way of putting the idea is that empty space still has a slight bit of energy associated with these quantum fluctuations, and this gives empty space an energy.  However, quantum mechanics predicts an immense amount of energy in the universe from this--far more than we actually observe.

[Farsight]

Yor-on: re stress being akin to pressure, see http://en.wikipedia.org/wiki/Pascal_(unit). Also see http://en.wikipedia.org/wiki/Stress-energy_tensor which says "In particular Tⁱⁱ (not summed) represents normal stress which is called pressure when it is independent of direction." JP's reference to the immense amount of energy is known as the vacuum catastrophe.

[yor_on]

Yes I know about 'vacuum energy' JP

But if you read the experiments done by Ken Olum there is no 'pressure' to the vacuum. What you have when you introduce those Casimir-type systems is a new relation that produces a effect not seen before that. There's a crucial difference between that and an 'pressure' existent at all times to me. It's back to square one in our discussion about potential energy, sort of

And whatever else sort of 'energies' we attach to the vacuum it will still only be a 'potential' energy as long as we don't 'manipulate it', and even then it seems as if we only will create a 'debt' needed to be payed back. Can you see my point here?

“No collection of Casimir-type systems in flat space can violate the ANEC,” Olum said. “This we succeeded in showing. So the next thing to do is to try this for interacting fields, and curved space.” Olum is skeptical of any exotic outcomes, however. There is no free negative energy lunch in the special case and, he suspects, there isn’t going to be one in the general case. “I have tried to construct these exotic things before, using what seemed to be promising ideas, and I have not been able to construct them. So I think that it’s impossible. And I have good reasons to think that it’s impossible,” he said. “Without constructing the proof, though,” he added, “one can’t be certain.”

Rivers of time

==
The way I think of it (pressure) may be expressed like this. A pressure should introduce retardation in a free, or if you like, deep space for objects moving in it, but there is no such effect that I've heard of? Or at least be noticeable as being something more than just gravitational forces even if equally 'pressuring' objects from all sides. Is this making sense


Furthermore I don't really know what 'space' is more than it is a 'distance'

[Geezer]

Furthermore I don't really know what 'space' is more than it is a 'distance'

Yoron: I think the "vacuum" idea is highly misleading. (Substitute "Electrolux" []) Seriously, "space" has very distinct, and quite measureable properties. If it was truly "nothing", why would it have any properties at all?

[JP]

I don't think Olum is ruling out the Casimir effect there.  I think he's just ruling out using it to extract energy from the vacuum, which makes a lot of sense.  That aside, I don't think anyone's questioning that there is some zero-point energy in the vacuum, the effects of which have been experimentally observed (the Lamb shift and spontaneous emission come to mind from quantum optics). 

Thinking of it as pressure is problematic because you would only see it as pressure (i.e. a force per unit area) if you construct a Casimir-type system.  Otherwise, you'd see it as energy fluctuations in the vacuum, whose (tiny!) forces would all average out to nothing when you looked at large objects.

And this is the reason why we got along so well for so long by saying the vacuum had zero energy and was completely empty.  In most cases, and for large objects, it averages to zero, so that classical theories work quite well by just assuming that the vacuum is completely empty. 

[LeeE]

No.

The steady state theory proposed that the universe always looked the same, including the expansion that we have seen since 1929. To account for this, the steady state theories proposed a field that created matter so that the average density of the universe remained the same. This means that the universe can always expand and always look about the same.

First of all, if the universe is expanding it is not in a steady state, but even if new material were to be created (by some sort of undefined field) in such a way that the universe 'looked' the same it would have to be in the form of 'new' galaxies, which although 'new' would have to appear to be 'old'.

[PhysBang]

First of all, if the universe is expanding it is not in a steady state, but even if new material were to be created (by some sort of undefined field) in such a way that the universe 'looked' the same it would have to be in the form of 'new' galaxies, which although 'new' would have to appear to be 'old'.

Well, you could take up this issue with everyone who worked on the steady state theory, but they've all abandoned it, so the point is pretty much moot.

[LeeE]

Why would I want to take up such a pointless and flawed issue, which I was, in any case, disagreeing with ?

[graham.d]

JP, I work in an industry that actually makes practical use of the Casimir effect. It seems to be widely assumed that this effect demonstrates zero-point energy, and it may do, but it is far from certain. There are other, more mundane, possible causes that can't be ruled out.

But, that aside, it does seem likely that there should be ZP energy. Can you explain why you think such spontaneous pair creation and annihilation would not create a pressure? Unless you assume that there is a sea of particles and virtual particles (those on the "other side" waiting to spring into existence) such that the virtual particles create a negative pressure balancing the positive pressure from those in existence at any one time. However, isn't a feature that dark energy has to have negative pressure to give the right sign for the cosmological constant to explain accelerated expansion? That is even harder to explain, although I admit I am looking this rather crudely.

Then there is the factor of 10^120 (or maybe only 10^55 with some other theories) of error! I think there is one thing everyone agrees on: nobody understands the reasons for the cosmological observations and the QM theory does not tie in with any of the current hypotheses in any consistant way.

[JP]

I should have set "net force."  I think you should get a pressure, but usually from all directions equally.  You wouldn't be able to see it except for in special cases, such as the Casimir effect, where you set up a system so that the pressures on both sides are unequal.

[graham.d]

I don't think you get no pressure, JP. A vacuum is not a vacuum if it has particles in it with a temperature that is not at zero Kelvin. That means there is a pressure. There is not net force on the walls of a box of air at the same pressure as the air outside the box, but it would be wrong to say that there is no atmospheric pressure, just, as you say, it is not exerting any net force.