311–318 of 318 posts
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How do you know?
Because measurements confirm a homogeneous and isotopic universe. A spherical universe would imply a special point, the center, which would go against these cosmological principals.
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From what I remembe of Undergrad physics this isn't actually possible. According to GR, within an event horizon, space-like pths become "time-like" which effecitvely means the singularity is unavoidably "in the future". No matter how big a black hole is, you can't just drift around inside it as literally all paths lead downward (hence even light not escaping) If you were inside a black hole you wouldn't be able to se…
All paths _eventually_ lead downward. Is there any limit to how long? Can't we just be near the outside of the blackhole and can't see the doom yet?
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Can you link the proof for these claims? I don’t see any obviously titled ones on Google Scholar, such as proving it’s impossible for turbulence to “introduce net angular momentum”.
I don't have anything more than Newton's third law for you and that its effects also hold in general relativity. The "far away parts of the universe are disconnected" is from my astrophysics courses back in university and the number of lectures to the cosmic microwave background, mostly coming from people discussing the Planck mission. But.. no, I don't have a convenient citation for you. And at least for the "angula…
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All paths _eventually_ lead downward. Is there any limit to how long? Can't we just be near the outside of the blackhole and can't see the doom yet?
There are no stable orbits inside the event horizon, and my understanding is even things like atom vibration can't move further from the sigularity so I'm guessing timespans would be limited!
I'll have to read up on that, I always had the vague sense that on ~finite scale of time there existed a region of space where you couldn't really tell the difference if you're inside of a big enough black hole or not.
Which sounds like I'm probably just wrong.
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What does "above" or "below" even mean in the context of something without a top or bottom? Or are you defining "above" to mean "the vantage point from which the galaxy appears to be rotating in the direction of earth clocks" for the purpose of this question?
Not to disagree with your justified Socratic questioning, but this sparked my interest and I figured I'd share my (novice!) TIL: it appears the IAU uses a coordinate system based on our solar system on January 1st 2000, 00:00 AM, or "J2000.0". Thus (0, 0, 0) is at the ~center of Sol and the x and y are within Earth's orbital plane, which means the z axis is orthogonal to that. In other words, it seems like "above"/"u…
I don't think I understand how your reply relates to the question either, though, because I was asking what it means to see other galaxies "from above" or "from below," when it seemed like that had to do with which direction they appear to be spinning from here.
Your answer is about what we consider "above us" or "below us," but we can still see a galaxy "below us" "from below" relative to it, if it (or we) are "upside down," and I couldn't figure out how we determine the orientation of "upside down" or "backward" for every other galaxy.
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It’s not possible for Alice and Bob to be within each other’s light cones but observe galaxies that aren’t in the other’s light cone? That seems wrong - there are galaxies that disappear from our light cone due to the expansion of the universe and they have neighbors that are still visible to us which would imply that the neighbors can still see the galaxy that became invisible to us. I’m willing to concede I don’t k…
It is about when they are or aren't in the light cones. If we remove relativity for a moment and define some time T=0, then Alice and Bob do see different things. The thing is that at 0, Bob and Alice aren't in each other light cones. Future Bob is in Alice's light cone and future Alice is in Bob's light cone, but at current they aren't. So you in the case of Alice, it is a question of what is in Bob's light cone. Th…
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There are no stable orbits inside the event horizon, and my understanding is even things like atom vibration can't move further from the sigularity so I'm guessing timespans would be limited!
Interesting, thanks. That does sound like you could tell from inside if you there or not. I'll have to read up on that, I always had the vague sense that on ~finite scale of time there existed a region of space where you couldn't really tell the difference if you're inside of a big enough black hole or not. Which sounds like I'm probably just wrong.
The way I see it is every surface inside an event horizon is another slightly "stronger" event horizon
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*raises the question
Off-topic, so I hope not to spark too much side discussion here. While I agree with your correction and this always bugs me, the common usage of the phrase "begs the question" seems to have become synonymous with "raises the question", as opposed to what I understand to be its former — and perhaps original — meaning which was associated with the informal logical fallacy by the same name.