341–350 of 502 posts
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It was mentioned during the press conference today that gravitational waves are not affected by interstellar/intergalactic dust the same way light is. In theory, once our detectors are good enough we should be able to use gravitational wave astronomy to peer all the way back to the big bang!
So, we'll finally be able to hear what god said at the start of the universe?
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The total mass of the Oort cloud is guessed at (3×10^25 kg), or about five Earth masses. With dark matter, we are talking about roughly 5.6x the amount of the total solar system mass. The Oort could would need to be about 371,691x more massive than it is. https://www.wolframalpha.com/input/?i=mass+of+the+solar+syst...
Could be an anthropic explanation for that. In a solar system with a hypothetically-"normal" Oort cloud, comets and debris from the cloud might wipe out life on the habitable inner planets every few hundred million years, never allowing it to advance to human-like levels. So we might be here only because our solar system is surrounded by an unusual amount of nothing.
Consider that we can currently detect differences in luminosity small enough to tell whether an Earth-size planet is passing between us and the star. A 5x mass Oort cloud would be thousands of times more mass than that. It would have noticeable effect on luminosity.
And, while our sun has an Oort cloud, there are a lot of stars out there that probably don't--too small, too big, too hot, too young, too old, etc.
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What do you think of the strong nuclear force? Gluons are the force carriers between color-charged particles. And gluons themselves have a color charge. So gluons transmit force between each other. Does that mean the universe is already too strange to exist? By the way, this is why the strong nuclear force has such a short range. Gravity has infinite range as far as we can tell, so that makes it unlikely that the gra…
How does the mediating particle being affected by the force translate to a shorter range?
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> A graviton wouldn't be able to escape a black hole ... the curvature of the spacetime around the black hole But isn't the curvature of spacetime around the black hole supposed to be the effect of its interaction with the graviton?? Is this where the translation from GR -> QM breaks down?
> Is this where the translation from GR -> QM breaks down? Sort of, to get a graviton you introduce perturbations on a background metric. (Basically small wiggles of spacetime around an 'average.') You don't do anything like that when you solve the Einstein equations. Consequently, the background spacetime ( that is, the black hole) is not really made of gravitons. (At least in some sense.)
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AFAIK no multiverse theory has yet been put forth that is experimentally testable (even in theory given infinite time, energy etc.) So it's not a proper (falsifiable) scientific theory at present, merely a (in my opinion wild) conjecture.
How about a theory where spacetime touches upon another spacetime and interacts with it, perhaps through gravity? Or if spacetime folds back onto itself?
Analogy: it could happen that tomorrow Jesus Christ descends from the heavens and brings the day of reckoning. That would prove Christianity to be true, but the fact that this could happen does not make Christianity a falsifiable theory.
A falsifiable theory is a theory that predicts something that we can (in theory) measure today (possibly requiring infinite resources etc).
Your second example (which is not a multiverse theory at all) is actually a good example of a falsifiable theory. People have calculated [1] that if spacetime was folded back onto itself at even just a single point, it would leave a distinct signature in the cosmic microwave background. We do not observe this signature, so we are pretty sure spacetime does not fold back onto itself.
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>how far we are from being able to create and detect gravitons // Surely we create gravitons whenever we move a mass just like we create photons whenever we move a body that interacts electromagnetically? Isn't the point that we're constantly exchanging gravitons with all matter as they mediate gravitational attraction.
I think you must be right -- but maybe there's some other way to create them, without needing to move a mass. The ability to manipulate gravity itself might be the key to space travel.
And maybe real hover boards
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This comment is making the page formatting gross. Those special characters with the strike-throughs make the entire page over-wide, thus requiring horizontal scrolling to read comments.
The browser layout engine should break on the spaces (Chrome does). They are just normal spaces, the combining character should have no effect. You have a bug somewhere. Also, I cannot edit nor delete it now, so tough luck! " " SPACE Basic Latin 0x0020 "̶" COMBINING LONG STROKE OVERLAY Combining Diacritical Marks 0x0336
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A "competing theory" would first have to match the GR predictions in all the other regimes where it's already been tested. But doing that is an extremely strong constraint on a theory, to the point where the only theory that can meet it is GR itself. Physicists know this because alternative theories to GR have been constructed and tested, and they have all failed. See, for example, here: https://en.wikipedia.org/wiki…
That's a very common sentiment, but a mistaken one. Theories do not get accepted only if they match the predictions of the previous theories. People value other features besides accuracy of predictions, like simplicity and explanatory power. Just recall how Kopernik's theory of solar system got accepted. It had worse predictions than Ptolemy's scheme at the time it was introduced; Ptolemy's scheme was way better in a…
> Just recall how Kopernik's theory of solar system got accepted. It had worse predictions than Ptolemy's scheme at the time it was introduced
Yes, and it wasn't accepted at the time it was introduced. Actually, Copernicus' theory in its original form was never really "accepted"; what was accepted was Kepler's reformulation using elliptical orbits, based on Brahe's more accurate observations. Kepler's model was more accurate than Ptolemy's, and that was a key factor in its acceptance.
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This comment is making the page formatting gross. Those special characters with the strike-throughs make the entire page over-wide, thus requiring horizontal scrolling to read comments.
The browser layout engine should break on the spaces (Chrome does). They are just normal spaces, the combining character should have no effect. You have a bug somewhere. Also, I cannot edit nor delete it now, so tough luck! " " SPACE Basic Latin 0x0020 "̶" COMBINING LONG STROKE OVERLAY Combining Diacritical Marks 0x0336