Understanding the Zero Energy Principle of the Universe

[Mark M]

Definitions are based on such assumptions, so call it what ever you want.

Right, but considering it's generally accepted that dark energy is a cosmological constant (See here), we arrive at the conclusion that it doesn't make a contribution to the energy density.

 

[twofish-quant]

Right, but considering it's generally accepted that dark energy is a cosmological constant (See here), we arrive at the conclusion that it doesn't make a contribution to the energy density.

It's not anywhere near that certain.

The problem with the current WMAP measurements is that there is a degeneracy between the curvature of the universe and evolution of the dark energy equation of state. The current results are consistent with zero curvature and zero evolution of the cosmological constant, but if both are non-zero, their effects will cancel each other out.

Now we *will* be able to establish that both are effectively zero pretty soon (just take more measurements to beat down the error bars in the next few years) but it's too early to declare this yet.

 

[twofish-quant]

What is more interesting me at the moment are other questions like how pressures of radiation and vacuum can be handled through thermodynamics, which originally is based on gases? Is this just a heuristic assumption or is there more behind it, that is, has radiation and vacuum pressure some similarity with gas pressure?

Nope. It's all hot gas. That's why people are pretty certain about the interpretation of things like big bang nucleosynthesis and the cosmic microwave background. They just involve gas and radiation for things that we can do Earth based experiments for.

One other good thing is that the "weird physics" for the most part does not effect the basic calculations that happen at between say 10 seconds and 500,000 years after event zero. The thing about dark energy is that it's a "constant" energy field which means that in the early universe, any pressure and energy that comes out of it is going be much less than "normal" gas and radiation pressure.

One weird thing about dark energy is that it doesn't seem to matter until very recently. This bothers a lot of people.

Another question is how infinite curvature at the big bang must be considered.

Some people take a look at the problem, throw up their hands and then look at some other part of the problem.

 

[twofish-quant]

Thanks Marcus for your search. However, I think that we cannot really crasp what happened at the big bang so research on that subject will always stay speculative in my humble opinion.

The cool thing is that this is *NOT* the situation, and we are likely to have a very good idea of what happened at "event zero" in the next decade. What you basically do is to take the data that is coming from PLANCK and WMAP, and "peel away the onion." You remove effects that happened at various times in the early universe, and what you have left is pretty close to event zero.

see http://www.cmu.edu/cosmology/events/cosmic-acceleration/will_kinney.pdf

The reason theorists are busy writing these papers is that we've got a lot of data that's coming.

 

[twofish-quant]

One other thing. It's tempting to say "the numbers look close to zero so they must be zero" but in this situation there are in fact good reasons to think that the both the flatness of the universe and the "constantness" of the cosmological constant could be close to zero, but not zero.

Getting a "flat" universe is a pretty generic feature of an inflationary universe. You take a curved object, blow it up, and it looks flat. So if inflation is right, we ought to expect a flatness of the universe near zero, but fluctuations in the early universe would set things up so that it's not zero.

Similarly, there are theoretical reasons why the cosmological constant may turn out to be non-constant. Either the dark energy is increasing, constant, or decreasing. If dark energy were decreasing then we wouldn't be here. The universe would have blown itself apart before stars formed and so we wouldn't see it.

So that means that dark energy could must be either increasing or constant. There are limits on how much dark energy could increase. At has to have started at zero, 13 billion years ago, and then gradually increased to it's current tiny amount, and that puts limits on how quickly dark energy has increased, and it turns out that distinguishing between dark energy that grows from zero to the current amount, and one that was always at the current amount is difficult.