Relativity, Black Holes and Gravitons

[FredLC]

Thanks, Peter; I'll have a look.

Regards .

 

[FredLC]

Two things: The cosmological constant was added for political/philosophical reasons by Einstein. However, it is theoretically possible to add the term to the field equations, which is quite special. The various properties the field equations need to have, gravely limit the possibilities for terms in the field equations. As such, it might be better to talk about models with cosmological constant 0 than about models without cosmological constant.

Interesting point, I never saw a suggestion that the solidity of the equations would prevent the insertion the constant as a random factor, even though I'd say that a random enough proposal could possibly be inserted anywhere.

On the topic, lemme suggest this excellent TED Talk from David Deutsch where he similarly, though more generically, argues that good explanations are those that do not admit random variation.

Anyway, I'll revisit my readings on the cosmological constant if I truly am misrepresenting its relevance...

Second, the cosmological constant is not just a language filler. It can be interpreted as the energy-density of vacuum. So it basically tells us how much energy a tiny bit of "nothing" possesses. Of course, the question then is, why does a piece of "nothing" have a certain amount of energy associated with it. A microscopic (quantum) explanation explaining correctly the energy density of the vacuum measured in astronomy would surely result in a Nobel prize.

On the energy of nothingness, I've read somewhere (can't pinpoint where, though) that as matter/anti-matter emerge spontaneously and nullify each other in the quantum scale, you have to consider that the wavelength function does not allow us to know exactly where, in a certain radius, will it physically manifest.

Ergo, the particles would emerge and instantly be "powered" with potential/kinetic energy, as the radius of the wavelength, much larger than the particle itself, has only a small probability of bringing them up perfectly rested in the soil.

So, energy would also appear out of nowhere, as none was used to take the particle to its unstable gravitational position, it simply spawned already there.

Gotta admit that this concept does not work where there is no gravity, or at the very least diminish the gravitational push to its "irrelevant" influence in quantum scale; but maybe a whole universe pushing those particles could make up for the vacuum energy...

Regards .

 

[classical_hero]

Fred, are you aware of the wonderful blog Starts With A Bang authored by Ethan Seigel? He has several posts dealing with dark matter, and a couple on dark energy.

He has a particular point of view, I'm sure other experts in the field may disagree with him. But I find his explanations very accessible.

Plus he uses lots of pictures

You mean he is using fudge factors to get his point across?

So much about standard cosmology is basically just guess work and untestable hypothesis.

 

[peter grimes]

You mean he is using fudge factors to get his point across?

Why would you think that?

So much about standard cosmology is basically just guess work and untestable hypothesis.

...says the young earth creationist

No, there are indeed tests! This is where science differs from dogma. You know that!

Feed different values for constants and forces into the models and you get universes that are unlike the one we find ourselves in. The reason there is as much certainty that there is something out there that currently is poorly understood (dark matter and dark energy) is because of all the converging lines of evidence from separate observations and theories.

Try actually reading a few of his entries and decide for yourself. And if you're still certain that he's wrong about something, or using a fudge factor, or whatever, then send him an email. I'll be surprised if he doesn't write you back.

 

[Serutan]

But when modern techniques brought about a second surprise - that the expansion was actually accelerating rather than slowing down - that raised some hairs, because there was no way to accommodate it within Gravity's einsteinian description.

Not quite. I went to an astronomy lecture by Micheal Turner on dark matter/energy
this spring, and he said (and showed) that Einstein's gravity equations allow for negative
results (i.e. dark energy), and said during an informal Q&A after the lecture
that at the moment it appears (but is not yet definitely proven) that GR does in fact
accomodate dark energy. There is a link to the lecture
video on this page.

 

[FredLC]

Not quite. I went to an astronomy lecture by Micheal Turner on dark matter/energy
this spring, and he said (and showed) that Einstein's gravity equations allow for negative
results (i.e. dark energy), and said during an informal Q&A after the lecture
that at the moment it appears (but is not yet definitely proven) that GR does in fact
accomodate dark energy. There is a link to the lecture
video on this page.

All right, I've seen the talk (gonna see the other ones now), and the only new info there (as it was for the laymen again, just as the others I saw before) was that the elasticity of the material can influence gravitational output to be negative. A big information that I'm still digesting, sure, but was it in the original theory of General Relativity, or was it an amendment to it?

I'd love to see that Q&A if there is a link available

Too bad that my middle-sized town has little or no hope of seeing an event such as that. Here in Brazil, I'd guess that São Paulo would be the single city where maybe one could get in touch with thew physics community...

If you live next to the university where the lecture were held, perhaps you can tip some of the physicists to reply my original question in this thread?

Regards .

 

[Serutan]

I'd love to see that Q&A if there is a link available

Unfortunately there is no such beast. It happened after the talk and official Q&A were
over - he was kind enough to hang around for almost 20 minutes to answer questions
from people who didn't get a chance to during the "on the record" part. He said there
was an "alternalte" explanation he didn't elaborate on for dark energy, but the the current evidence pointed
towards GR. I am not familiar enough with the theory to know how much (or not) it
has been modified over the years (besides the infamous 'cosmological constant').
He never mentioned it being a new addition to the theory; I was left with the impression (FWIW) that this was something that had been implicit in the theory
all along, but that no one thought anything about it until dark energy reared its head.