The Nature of the Universe

[fuindordm]

For all those interested in cosmology, relativity and astrophysics:

We just had a press release from the folks studying the expansion of the universe, the acceleration of that expansion, and the cosmological constant.

http://www.edpsciences.org/journal/...iv1=others&niv2=press_release&niv3=PRaa200512

The first year's worth of data from measuring the distances to far-off supernovae are in, and the results are impressive. Not only has the acceleration been confirmed and measured to 10% precision, but they've determined that the 'dark energy' is wholly consistent with Einstein's cosmological constant. The physical origin of the cosmological constant is still unknown, but the article notes that the magnitude of the vacuum energy density required is still 10^60 times LESS than the lowest estimates from particle physics.

And yet, not zero. Everything would have been so simple if it had been zero... the eternal lament of physicists.

Enjoy!
Ben

 

[Zappo]

Correct me if I'm wrong, as I'm not an expert. Einstein's cosmological constant was required to make the universe static over time. It was rejected with the acceptance that the universe isn't static.

This "new" cosmological constant is required to explain the acceleration of the universe's expansion. How can it be "consistant" with Einstein's constant? Numerically, I mean.

 

[fuindordm]

Correct me if I'm wrong, as I'm not an expert. Einstein's cosmological constant was required to make the universe static over time. It was rejected with the acceptance that the universe isn't static.

This "new" cosmological constant is required to explain the acceleration of the universe's expansion. How can it be "consistant" with Einstein's constant? Numerically, I mean.

You have it right. Einstein proposed it because (a) an arbitrary constant was allowed by his equations, and (2) because he wanted a steady-state universe, but since gravity inevitably caused the universe to collapse, a repulsive force was necessary to establish equilibrium. He quickly scrapped this model, however, both because it was an unstable equilibrium at best and because Hubble and Leavitt had recently discovered that the redshifts of distant galaxies indicated an expanding universe.

So for about 70 years everyone was happy with the standard Big Bang model... an evolving universe, and the cosmological constant set to zero because it makes more sense for *any* unconstrained constant to be zero.

Then in the 1990's people started studying distant supernovae and finding that Hubble's famous linear relation wasn't entirely linear... and that the wrinkles in the cosmic microwave background didn't quite look like what was expected either. So the cosmological constant was re-introduced and became a major player in cosmology again.

It looks to me like it's here to stay. No one expected it to make a comeback, but there you are!

Ben

 

[Umbran]

We just had a press release from the folks studying the expansion of the universe, the acceleration of that expansion, and the cosmological constant.

Smallest of quibbles - "the folks"? As in "all the folks"? As if every cosmologist on the planet was in on it?

Kind of like saying that 3e was published by "the folks who develop rpgs..."

 

[fuindordm]

Smallest of quibbles - "the folks"? As in "all the folks"? As if every cosmologist on the planet was in on it?

Kind of like saying that 3e was published by "the folks who develop rpgs..."

I'll take that quibble as a bump.

There's only one research team studying the supernovae, which give the most direct picture of the universe's expansion history--it's an extension of the Hubble diagram relating redshift to distance. Other research teams are approaching the problem from different directions, studying the large-scale distribution of matter in the universe (e.g. the Sloan Digital Sky Survey) or the cosmic microwave background (the WMAP and Plack satellite experiments).

Cosmology has entered the era of Big Science, where the research groups are growing to dozens of people and grants of tens of millions of dollars.

Ben

 

[Desdichado]

Smallest of quibbles - "the folks"? As in "all the folks"? As if every cosmologist on the planet was in on it?

Kind of like saying that 3e was published by "the folks who develop rpgs..."

Hey, Umbran--try clicking on the link; the authors of the press release are listed.

 

[Angel Tarragon]

Not a professional opinion - just one that is mine: When the universe has expanded to its limit, it will start to shrink.

 

[Umbran]

Hey, Umbran--try clicking on the link; the authors of the press release are listed.

Yes, I know. And I did click on the link. I wasn't objecting to the press release itself. I was commenting on the reporting about the release. Science news reporting is generally done poorly. And it won't improve unless someone speaks up.

 

[fuindordm]

Not a professional opinion - just one that is mine: When the universe has expanded to its limit, it will start to shrink.

There's not enough stuff in the universe for gravity to pull it back together, so some other mechanism is needed.

There are still some viable cyclical universe theories out there, but they're all tied up with string theory (bad Ben! no biscuit!) and the details are beyond my ability to judge. In essence, they propose that the universe will undergo another phase transition when dark energy dominates, provoking another 'Big Bang' period of exponential expansion and matter-energy creation.

Here's a mind-boggler for you: if the universe is expanding, then what is it expanding into? Some scientists are comfortable with the universe being infinite and yet expanding--after all, if you multiply infinity by five you don't get a higher order of infinity. Others think that the universe is finite (but very very large), and postulate that the Big Bang is just a bubble forming in a higher-energy medium.

Ben

 

[Turanil]

Here's a mind-boggler for you: if the universe is expanding, then what is it expanding into?

Infinity or not infinity: I think I got a headache...