How much of Einstein Online have you read?

[Martin]

Einstein Online is an amazingly informative website that the AEI (Albert Einstein Institute) started in 2006 and is still adding to.

 

They have a section on cosmology that is the best introduction I know of not requiring a lot of math. Indeed it is math-free but still manages to be up-to-date and accurate, which is quite an accomplishment.

 

To get there, google "einstein online spotlights cosmology".

 

They have other sections that spotlight other topics as well, like relativity, black holes, quantum theory,...

 

The section that spotlights cosmology has 8 articles they call basics, plus some extras that go beyond those 8 basics.

 

I'm wondering how many other people besides myself have been reading Einstein Online, particularly the cosmology basics.

 

If you too have visited the site, which of the 8 cosmology basics have you read?

 

If you have read one or more you want especially to comment on or recommend, please post the name(s) or link(s)!

 

Which of these have you read? (The poll allows multiple answers.) If none just check option 9.

 

1. The shape of space

2. Cosmic sound: curvature and the cosmic background radiation

3. A tale of two big bangs

4. Big bang nucleosynthesis

5. Equilibrium and change

6. Elements of the past

7. The mathematical universe

8. Of gravitational waves and spherical chickens

9. None read (at least so far)

[john5746]

thanks for the reference! Awesome site.

 

I read the following:

 

Avoiding the big bang

Taming infinities with loops

Searching for the quantum beginning of the universe

A tale of two big bangs

 

Have a question regarding loop quantum gravity. Does it predict or have an explanation for the contraction of the universe?

[Martin]

thanks for the reference! Awesome site.

 

I read the following:

 

Avoiding the big bang

Taming infinities with loops

Searching for the quantum beginning of the universe

A tale of two big bangs

 

Great! You are voracious reader. I particularly liked the piece called A tale of two big bangs. I had never heard the issue of what people mean by it discussed like that, and it checks out with my experience. I realized that there are actually two distinct meanings.

 

There was another keen observation in the same section, that showed the author was familiar with cosmologists and their informal shoptalk. I will try to find it.

 

Have a question regarding loop quantum gravity. Does it predict or have an explanation for the contraction of the universe?

 

Loop QG applied to cosmology is sometimes called Loop Quantum Cosmology. And it's still early days for LQC. It doesn't, is the simple answer. In a typical LQC computer run, they put in some parameters---like some matter, maybe something like dark energy, maybe not, try different things---and typically all they get is that there is a prior contraction phase. they have no idea where it comes from. there may just be one bounce, or there may be several. Let's focus on the single bounce case.

 

As far as I've seen, all that happens is the universe contracts to a certain very high density and then quantum effects take over and (quantized) gravity begins to act different from usual and turns repulsive, and there's a bounce and the universe expands back to less extreme density at which point things behave normally.

 

As far as I've seen, they don't answer any Big Questions, they just are working on a simple quantization of the standard model universe that will allow them to run time back past the blow-up.

And that will then allow them to make predictions about early universe structure aspects that will make their model testable.

 

As far as I know, no one has been asking "where did it come from".

I suppose that day might come, when they ask that, but there is a lot to do before that day arrives:D

 

I liked that question. It was fun trying to answer it. I'm not a QG expert. I'm just an interested observer of that research scene.