Physics question, re. why the sky is dark

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Re: Physics question, re. why the sky is dark

Postby Giles on Fri May 22, 2020 6:37 am

Steve James wrote: Will the universe end in a big rip or will something reverse the expansion and lead to a big crunch?


Should at some point the expansion reverse then it should be quite 'obvious': all those distant galaxies and super-clusters will go into blue shift.
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Re: Physics question, re. why the sky is dark

Postby Steve James on Fri May 22, 2020 7:16 am

Trick wrote:Dark matter and dark energy take up 95% of the whole darn thing, no wonder it’s so dark.


Dark matter is matter that scientists predict is there because it has a gravitational effect. Dark energy, otoh, is the force predicted that is causing the expansion of space. Something must be making it happen and accelerating it.

Um, fwiw, ignore the math and it will make more sense. The "cosmological constant" is the c in Einstein's formula.

The question is whether they are related the same way matter and energy are related (a la Einstein's formula)?
Here's a video by one of the newer professors at my old school. He has a great series on PBS/Youtube.

https://www.youtube.com/watch?v=UwYSWAlAewc
Last edited by Steve James on Fri May 22, 2020 7:24 am, edited 1 time in total.
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Re: Physics question, re. why the sky is dark

Postby Steve James on Fri May 22, 2020 7:48 am

Giles wrote:
Steve James wrote: Will the universe end in a big rip or will something reverse the expansion and lead to a big crunch?


Should at some point the expansion reverse then it should be quite 'obvious': all those distant galaxies and super-clusters will go into blue shift.


Just saw this. Yes, if it reversed, but nowadays they don't think that's possible. There isn't enough matter (or dark matter) to create the gravity (to deform space/time) to overcome dark energy (that is increasing the acceleration).

Of course, the problem is that it's mind-boggling and not intuitive. It's quite possible that the acceleration will slow down at some point. We intuitively think in Newtonian terms. But, the only way we know of the universe's expansion via dark energy is math; the same for dark matter. They are things that, so far, we literally cannot see.

Hey, seeing is overrated. We are made of atoms, and atoms (ok, H atoms) are 99.9% empty space (and we're mostly H2O). That doesn't mean we're nobodies, does it? :)
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Re: Physics question, re. why the sky is dark

Postby Dmitri on Fri May 22, 2020 1:59 pm

Steve James wrote:...the only way we know of the universe's expansion via dark energy is math; the same for dark matter. They are things that, so far, we literally cannot see.

That point cannot be overstated. I am convinced there will be some new discoveries (which we're probably unlikely to witness) that will cause dramatic changes to some of the current views, including Heisenberg principle, Planck length, etc.

Here's a very good article:
https://www.forbes.com/sites/startswith ... -in-nature
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Re: Physics question, re. why the sky is dark

Postby Steve James on Fri May 22, 2020 3:00 pm

Well, Dmitri, the thing about math is that it can be disproven. There's a good Youtube vid by a (ex) colleague on the "Crisis in Cosmology."

I saw the Forbes article earlier, and it's true that the universe is not just math. But, that's far from the issue. All of modern physics is based on using mathematical calculations, and without math we wouldn't have a way to explain or test them. I.e., through some form of measurement. Planck length is an example. If there's something smaller, how do we measure it? Is there another (testable/falsifiable) way for humans to understand it?


https://www.youtube.com/watch?v=72cM_E6bsOs
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Re: Physics question, re. why the sky is dark

Postby Dmitri on Sat May 23, 2020 6:57 am

Is there another (testable/falsifiable) way for humans to understand it?

What I'm saying is that there will be one in the future.
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Re: Physics question, re. why the sky is dark

Postby Steve James on Sat May 23, 2020 7:06 am

Dmitri wrote:
Is there another (testable/falsifiable) way for humans to understand it?

What I'm saying is that there will be one in the future.


How will you know it's better without math? There's little doubt there'll be more methods, just none without math --to confirm any theory.

Dmitri, re: math and physics, the most important book in physics before the 20th century was written by a bloke named Newton. It described the laws of gravity, etc., developed "calculus," etc. Well, people call that book "the Principia," but the title is "The mathematical principles of natural philosophy." Newton used math because he wanted to avoid the bullshit.

Btw, Einstein was good at math, but depended on Emmy Noether to do the proofs of his theories. None of his theories has been disproven, even though many -like time dilation- are still counter-intuitive. It's only math that proves it. If the math comes out wrong for any Einstein theory, it is automatically disproven.

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https://galileo.ou.edu/sites/default/fi ... 000-tp.jpg

In cosmology, you are free to come up with your own explanation of the universe. And, you can deny anyone's explanation. If you can't prove/disprove it with math, it's ... nice to have an opinion. :)
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Re: Physics question, re. why the sky is dark

Postby Dmitri on Sat May 23, 2020 10:48 am

:-\ When did I ever suggest math was useless?
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Re: Physics question, re. why the sky is dark

Postby Steve James on Sat May 23, 2020 12:38 pm

I know you don't think it's useless.
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