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(Guardian)   Has the problem of Dark Energy been solved by Massive Gravity? Once we get the gravitational wave telescopes up and running, then we'll know for sure. Maybe we should get Space Farce involved   ( divider line
    More: Interesting, General relativity, Universe, Dark matter, Prof Claudia de Rham, Physical cosmology, De Rham, inward tug of gravity, latest acknowledgement of the breakthrough  
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1057 clicks; posted to Geek » on 26 Jan 2020 at 4:02 AM (34 weeks ago)   |   Favorite    |   share:  Share on Twitter share via Email Share on Facebook

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2020-01-27 8:41:09 AM  

t3knomanser: The very fact that you use "in a vacuum" shows that you don't understand what c is. c is a constant outside of a vacuum too. Light often moves slower than c because it stops to interact with intervening matter, so the speed of light itself is not a constant, but c is.

Yeah, I muddled my terminology a bit, but you're still missing the fundamental point. *c may not be a constant*. In this model, it would still be the upper speed limit of causality, thus of light in a vacuum, but it would be dependent on local gravitational density.

And as for how strong the gravitation is here on earth/local curvature of space, we're not talking about the local g. We're talking about the cumulative local gravity. Which in a solar system is many orders of magnitude higher than in intergalactic space.

Let me explain it this way - if you have a star, light bends around it, yes? This is because of the local curvature of space-time due to the gravity of the star (speaking very abstractly here, not getting into the details). If you run your light beam past the sun, at say, the average orbit of Mercury, you'd see a noticeable but small bend in the path of the light. Now place a second star equally distant from the light beam so that the beam is passing directly the center point between the centers of the two stars. You'd see no bend.

Now examine the same beam in a theoretical section of space where there are no stars, no *nothing*. Nothing to create gravity at all.

In the current model, those two beams are going to have the same speed. The idea I'm positing is that they won't. The local space between the two stars may be flat, but it sure as heck isn't identical to the space with nothing anywhere near by. Now pile in the cumulative effects of being in the middle of a galaxy. Sure, those star systems have progressively smaller effects as you move away from us, but they do have an effect. Our local space is *gravitationally dense*, even where it's flat. Intergalactic space is a lot "looser" or "less dense", gravitationally speaking.

t3knomanser: If c weren't a constant, gravity wouldn't work as we observe it to work.

Under. the. current. model. You need to add this to every sentence you say, because you can't seem to escape it. Literally EVERYTHING you say has this postpended to it. We don't fully understand how gravity works. We have a model of it. And our model is predicated on the fact that c is constant, so of course c has to be constant for our model to work. Our model is broader than Newton's was, but it doesn't encompass everything. We piece together bits of it for non-local areas based on ASSUMPTIONS about how things work outside the local area. Those assumptions start with c being a constant. You can't then use them to prove it must be everywhere the same. You can say that the model is consistent with our observations if we ignore the parts we can't explain and we keep patching the model to keep up. But like Newton, the model itself may have an underlying flaw due to our limited circumstances that we can directly verify without it.
2020-01-27 9:51:18 AM  

Gordon Bennett: FarkaDark: dryknife: Arguing about physics on Fark is stoopid, when there are "I lahk hur, she purdy" comments needing to be made.

[ image 300x180]

You mean like
I'd teach her the meaning of Plank's Constant
/I am so shameful

You think a theoretical physicist needs to be taught the meaning of Planck's constant?

Well she might know about it butt has yet to experience it.
2020-01-27 9:52:58 AM  

PainInTheASP: Dark energy is God playing hockey with the observable universe. Prove me wrong.

In no religion is there any mention of God using the following words:
Big city slams
2020-01-27 11:58:32 AM  

Guildmaster: Yeah, I muddled my terminology a bit, but you're still missing the fundamental point. *c may not be a constant*. In this model, it would still be the upper speed limit of causality, thus of light in a vacuum, but it would be dependent on local gravitational density.

I think the reason you are getting arguments is that c being a constant is not really anything so trite as an assumption. If c changes, then everything changes.  Like, the distance between atoms would change because causal time in which particles react gets larger or smaller.  And so on.  And once everything changes (and everything would change together, and in the same way because pretty much everything depends on c), it's like nothing changed at all.  If the room you're in grows larger, but the ruler also grows, as well as your own body, how will you know?
It's not unlike the parallel postulate for Euclidean.  It's an assmption, yes, but the whole of Euclidean geometry is so wrapped up in it, if you change it you have a completely new kind of geometry.

Because everything in our current model is so highly dependent on c, the only way a change in c would matter is if you could find something that had some degree of independence from c (fine structure constant maybe?  I don't know), and then show that if c changes, that thing won't change in such a way that everything will remain the same.  But here's the funny part about that: in that case, scientists would almost certainly prefer to say c is still constant, and it's that other thing that changes.
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