What is spacetime?

72MachOne99GT

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I didn’t know we were going straight around a warped space. I just thought we orbited around.

Learn something new every day. Well, maybe every other day.
 

James Snover

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What I’ve learned is that you nerds get laid a lot less than some us.

Just keep telling yourself that. Chicks dig gravity. They’re all about General Relativity. Can’t keep their hands off a guy who knows his Special and General Relativity. You walk into any bar and start talking Mach’s Equivalence Principle or Lorentzian Compression, you better be ready for full night of bed-frame destroying non-stop action. Know why most physicists are skinny? Because they have to prioritize cardio. They _have_to.


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James Snover

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Conversely, what keeps gravity from essentially crushing us? I understand the earth’s gravity is weak, relatively speaking, but I always thought gravity counteracted the also weak centrifugal force. That’s the suspected reason behind the earth bulging along its equatorial diameter compared to its polar.


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The only thing that keeps gravity from crushing is the fact that atoms will only compress so far under ordinary conditions. Earth doesn’t have anywhere near the mass to do that.

When you get up to the size of stars, then gravity starts forcing atoms to fuse by crushing them beyond their ability to resist. And yet, even in stars, atoms are still fairly discreet items.

When you get a neutron star, though, now gravity is so strong it crushes the electrons and the nuclei of the atoms together, creating neutrons. The atoms resistance to being crushed together is completely overwhelmed.

The only thing denser, with higher gravity, is a black hole.


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ShelbyGT5HUN

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This whole "curved space time", was proven back on May 29, 1919, during a solar eclipse. Stars that were "behind" the sun, became visible during totality, because of the curving of space by the sun, allowing their light rays to be seen.
 

wizbangdoodle

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That video is fine and dandy, but the sun(and associated planets) don't sit on a 2 dimensional plane. We also tend to look at things as up, down, side to side. Who's to say that the galaxy shouldn't be viewed vertically? What are the 3 dimensional effects of mass?

Move on, nothing to see here.
 

wizbangdoodle

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Ok, nevermind. After thinking about this a bit, it dawned on me that the video and other representations are only showing 1 plane for clarity and simplicity. In actually, it would form a "bubble" of warp around the sun.

Move on, nothing to see here.
 

DaleM

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Your son has got a sharp mind! Can't wait to see what the young man will do with it, in time.

I'm going to intersperse the replies in your original post, hopefully to avoid confusion:
55 bucks for the hard back. Holy hugeness. This book is so heavy it is creating its own black hole.
IMG_20210413_135245.jpeg


OK Bozos, stop clowning around.
 

thomas91169

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To conceptualize spacetime, I believe, will require 4th dimensional thinking. We barely do three dimensional thinking. On top of which, we are limited to what our physiology allows us to perceive of the universe, which is insanely small range of things compared to what's going on at any given moment.

Also, the further I get into engineering studies, the more I realize the idea of spacetime or gravity is likely just waiting for some genius to create some set of mathematical equations to solve. The whole F=ma and all that jazz, but the gravity or spacetime equivalent of it.
 

BigPoppa

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I've always loved General Relativity.

If spacetime can be compressed, which is what we perceive as gravity, does that mean that the universe is finite? If not, how can it be compressed if it is infinitely expanding?

If it is infinitely expanding, does spacetime compression indicate that the compression of spacetime occurs at a faster rate than the expansion of the universe?
 

72MachOne99GT

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What blows my mind absolutely out of the water is the concept of time being bent, or non-linear.

How can someone standing in one place experience the equivalent of 24 hours, and someone else standing somewhere else not experience 24 hours in the “same” timeframe.
 

BLOWN PONY

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I knew I was going to feel dumb for clicking a Snover post.
Turns out I was correct.
 

James Snover

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To conceptualize spacetime, I believe, will require 4th dimensional thinking. We barely do three dimensional thinking. On top of which, we are limited to what our physiology allows us to perceive of the universe, which is insanely small range of things compared to what's going on at any given moment.

Also, the further I get into engineering studies, the more I realize the idea of spacetime or gravity is likely just waiting for some genius to create some set of mathematical equations to solve. The whole F=ma and all that jazz, but the gravity or spacetime equivalent of it.
Yep. Whoever figures out how we can manipulate gravity like we do electromagnetics is going to go down as the most significant person in history.
 

James Snover

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To conceptualize spacetime, I believe, will require 4th dimensional thinking. We barely do three dimensional thinking. On top of which, we are limited to what our physiology allows us to perceive of the universe, which is insanely small range of things compared to what's going on at any given moment.

Also, the further I get into engineering studies, the more I realize the idea of spacetime or gravity is likely just waiting for some genius to create some set of mathematical equations to solve. The whole F=ma and all that jazz, but the gravity or spacetime equivalent of it.
Yep. Whoever figures out how we can manipulate gravity like we do electromagnetics is going to go down as the most significant person in history.
I've always loved General Relativity.

If spacetime can be compressed, which is what we perceive as gravity, does that mean that the universe is finite? If not, how can it be compressed if it is infinitely expanding?

If it is infinitely expanding, does spacetime compression indicate that the compression of spacetime occurs at a faster rate than the expansion of the universe?
Actually, parts of the universe have been expanding faster than the speed of light from the moment it was created. Or so goes some of the current thinking. Can't help but think they're on to something.
 

James Snover

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Ok, nevermind. After thinking about this a bit, it dawned on me that the video and other representations are only showing 1 plane for clarity and simplicity. In actually, it would form a "bubble" of warp around the sun.

Move on, nothing to see here.
Here's my unanswered question: Does the universe spin? Everything in the universe does spin. Conservation of angular momentum seems to be an absolute. So: does the universe itself spin? And how could we tell, if it does? Or doesn't? And what would the answer, either way, mean to us?
 

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