Has physicist's gravity theory solved 'impossible' dark energy riddle?

www.theguardian.com ^ | Sat 25 Jan 2020 06.40 EST | Hannah Devlin Science correspondent

[discostu]

Not really. Dark Matter theory is really just a place holder. It says there’s something there we haven’t found that makes the math work. If it’s gravitons it actually proves the theory, by finding the thing that makes the math work.

[TheNext]

The greatest question is with a 45 billion radius universe, how did WE get here?

And why here?

Where else have we been and where shall we future be?

[Boogieman]

“would gravitational waves ripple back to the center once it reached the edge of the expansion?”

Yes, probably, but a couple problems:

* Normal gravitational effects happen instantaneously, not through gravitational waves. Gravitational waves only happen when there is some sudden change in the local spacetime geometry, like two massive bodies colliding or a black hole being formed, something like that.

* Gravitational waves can only travel at the speed of light, and the rate of the expansion of the universe is high enough that gravitational waves from the center of the universe would never be able to reach the “edge” to bounce back. Even if waves starting near the edge of the universe could reach it and bounce back, they would be swimming against the current and wouldn’t get very far back towards the center.

[Boogieman]

“They tell us that 97 or 98% of the “visible” universe, is moving away from us, due to universal expansion (space itself is expanding) faster than the speed of light...”

Ok the problem is you are confusing two different facts. One fact is that 97-98% of the visible universe is moving away from us. A separate and distinct fact is that the universe is expanding faster than the speed of light. You can’t put those together and conclude that 97-98% of the stars and galaxies are moving away from us faster than the speed of light, because most of them are not.

Think of the universe like a balloon. As it inflates, the distance (measured along the surface) between our dot on one side of the balloon and a dot on the other side of the balloon expands very quickly. But the distance between our dot and a dot right next to us expands much more slowly. So the farthest points in the galaxy are moving away from us faster than the speed of light, but the closer ones are not.

[HamiltonJay]

I understand that the speed of expansion is proportional to distance.

97-98% of the visible universe moving away from us faster than the speed of light, was a quote from someone on one of the Science channel shows... I have to assume that he misspoke when he stated this, if this is not the case.

Because my brain instantly went to, if 98% of the visible universe is moving away from us faster than the speed of light, how is it we even see the “visible universe” at all.

[Boogieman]

He must have misspoke, or maybe he was just being dramatic. But yeah, we wouldn’t see many stars at all in the sky if 97% of the universe were moving away from us that quickly.

[yesthatjallen]

Dark Energy: The Universal Fudge-Factor

[mlo]

"...Seems to me that explanation would blow a huge hole in the Big Bang theory, because, my understanding was that the Big Bang occurred when the universe collapsed into a very small, tightly compacted mass."

No, the Big Bang does not include the premise that the universe collapsed into a dense state. The theory starts with the universe in that state. What happened before that, if anything, is external to the theory.

Both ideas, dark matter, and this gravitons with mass, necessarily include the Big Bang.

[mlo]

"If gravity has waves then would gravitational waves ripple back to the center once it reached the edge of the expansion?"

Gravitational waves travel at the speed of light. The entire observable universe is too large for them to traverse and reflect back, if they were to do such a thing.

Which they wouldn't. The entire universe is larger than what we can observe, and we have no way of knowing just how large it may be. And an "edge" to it isn't going to be the sort of classical boundary you are familiar with, as there would be no space on the other side.

[SuperLuminal]

"Anyway, these are the sorts of questions Insomnia sometimes brings..."

Here's the answer... Just factor the so-called graviton "mass" into the Stress-Energy Momentum Tensor and re-figure the Cosmological Constant...

Sleep soundly... {:-)

R_mn - 1/2g_mnR + g_mnΛ = 8πG/c⁴T_mn

R_mn==Ricci Tensor (which is derived from Riemann Tensor)
m==mu (Summation Index)
n==nu (Summation Index)
g==Metric Tensor
R==Ricci Curvature Scalar (Derived from Ricci tensor)
Λ==lambda = Universal Cosmological Constant (Expansion/Dark Energy)
π ==PI== (My favorite is strawberry-rhubarb)
G==Gravitational Constant
c==Speed of Light
T==Stress-Energy Momentum Tensor

[gnarledmaw]

Unless our universe is the inner bubble in a ball of universe bubbles then there is a different universe on the other side...then again, maybe its just the raspberry filling inside a giant jelly donut.

[Larry - Moe and Curly]

Thanks, Sword.

I know you’re aware of Suspicious Observers, but a good intro to the plasma universe (where we really live), including recent discoveries. Dark matter not required.

It’s about an hour long, but if you’re interested in this subject...:

https://youtu.be/E4pWZGBpWP0?t=25