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Bit of an aside, but: > But physicists seek the more fundamental, quantum theory of gravity that underlies Einstein’s picture; it’s this quantum gravity theory
by uoaei 3y ago
Bit of an aside, but:
> But physicists seek the more fundamental, quantum theory of gravity that underlies Einstein’s picture; it’s this quantum gravity theory that governs extremes like the Big Bang and black holes. And one way to inch toward this complete theory is to study quantum fluctuations in the space-time fabric.
I'm uncomfortable with the implicit framing that quantum gravity is The One True Theory and we just need to figure out how to formalize it. I'm sure this comes from the author and not the researcher, maybe something was lost in translation from the technical to the colloquial, but nonetheless it is still inaccurate to say that there is any kind of certainty that this is the right path forward. (Ditto for dark matter and dark energy, though those could more accurately be described as lacks of models than models per se.)
- ndsipa_pomu 3y agoWhat other approaches are there that wouldn't lead to a quantum theory of gravity?
- trhr 3y ago[flagged]
- quickthrower2 3y agoAre you hinting at infinitesimals?
- trhr 3y agoNo, those are fine. Well, almost. They're not uniquely broken, at least. Mathematics would have me believe "the sum of all positive integers" is a negative number. They can provide glorious proofs of that fact. When you insert the result into the physics equations, the equations work. But the idea is, on its face, stupid. Any child would tell you as much. The equations only "work" on that premise because they're almost right. But that's not a problem with infinity, it's a problem with something we're assuming when we go to write the proof in the first place. And whatever that problem is... it's almost certainly the thing stopping us from solving the Riemann hypothesis.
- ndsipa_pomu 3y agoThere's more than one "math" system and Riemann Spheres allow division by zero. How does that help visualise the universe?
- trhr 3y agoOh, you mean the system that defines pi to be infinity minus infinity? That's the one that's correct? Okay, good luck with that.
- dang 3y agoCan you please stop posting unsubstantive comments and definitely please not post in the flamewar style to HN? You've done that a lot in this thread and it's not what this site is for. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
- tnecniv 3y agoYou could define the Big Bang to be at any value of t, i.e., pick t0 > 0. Such a shift changes nothing and won’t fix any singularities in the dynamics.
- trhr 3y agoYou, by definition, cannot. Our best science suggests that `t` ceases to be a linear value at t=0. It's why we define t=0 to be there. The problem is the absurdity of the idea that `t` could ever cease to be a linear value. Causality is a fundamental truth. To lose the idea of "before" and "after" is to lose causality. If your fundamental theorem of the universe requires you to forego causality, you should consider looking elsewhere.
- Attrecomet 3y agoThis is literally just a string of buzzwords connected to form a grammatically correct sentence.
- trhr 3y agoGoedel, Russell, and Frege proved from first principals that our understanding of basic arithmetic cannot be both complete and consistent. One or the other, but not both. If children's arithmetic cannot be proven complete and consistent, what does that say about the sort of math used to define the universe? Building upon a broken structure is how you get broken results.
- mhh__ 3y agoIronically zero is the only number unlike any other number.
- trhr 3y agoFair. I misstated my premise. "Find the math that allows zero to be treated like any other number, or, find the math that treats it like it's definitely the wrong answer." Consistency is the key. What we have now is only locally consistent. You can break it into pieces with set theory, geometry, etc. You're never going to find a unifying equation in a version of mathematics where geometry and algebra don't mesh.
- uoaei 3y agoThere is more focus of late on theories of "emergent gravity", i.e., that gravity is not a fundamental force. The most interesting one to me is so-called "entropic gravity", which also resolves the issues plaguing the theory of dark matter and gives credence to MOND. Such theories have been long derided by old-school physicists raised in the golden era of quantum mechanics (and their acolytes), but have surprisingly powerful explanatory power that other theories cannot achieve without tacking on seemingly arbitrary or else otherwise unmotivated factors. Dark matter especially has always been suspect to me, since even after all this time, it is defined as little more than "the gap between our models and observations" with no strong underpinnings that would explain its existence in satisfying ways. I am not affiliated with this blog in any way but find the arguments compelling: https://tritonstation.com/ https://tritonstation.com/ Here's an interview with a researcher who is also trying to move beyond quantum formalisms for spacetime vis a vis gravity: https://www.quantamagazine.org/the-physicist-who-bets-that-gravity-cant-be-quantized-20230710/ https://www.quantamagazine.org/the-physicist-who-bets-that-g...
- klyrs 3y agoMy understanding is that quantum gravity is a gaping hole in our theoretical understanding of the universe, and until that hole is plugged, we have no hopes of finding a One True Theory. That's quite different from quantum gravity being The theory.
- uoaei 3y agoWhat I was trying to get at is that gravity may not even be quantized. The insistence that it act like the other three fundamental forces is a holdover from earlier interpretations of physics but in retrospect there's still no solid reason to assume it has to be quantum at all.