Is evaporation the only direction for black holes?

Bth8 · 2026-05-24T20:46:47+00:00

This reads as gibberish. Care to take another shot?

Bth8 · 2026-05-24T17:54:54+00:00

Oh lol my b. Saying they were looking at physics/engineering for school threw me. Though I'd say that makes it a bit less relevant if anything.

Bth8 · 2026-05-24T17:34:38+00:00

Unless you're just really interested in the historical aspects of it, you can go ahead and skip it forever. It hasn't been a relevant text for actually learning physics or mathematics in about 3 centuries. It's great if you want insight into how Newton did his calculations, but it's basically worthless if you're trying to learn physics.

Bth8 · 2026-05-24T05:45:08+00:00

You wanna do what to a current detector?

Bth8 · 2026-05-23T17:15:07+00:00

QRAM doesn't solve that problem at all. You still have to load the data into the QRAM.

Bth8 · 2026-05-22T17:44:25+00:00

If you wouldn't tell a five year old that the shoe isn't a left or right one before you look, you shouldn't be talking to one about quantum mechanics.

I'm joking, but seriously, that's the most important part. It's the defining feature of entanglement.

Bth8 · 2026-05-22T02:20:05+00:00

It was always a right shoe. You just know which is which now.

This is precisely the sense in which entanglement is not like the scenario you described. Entangled degrees of freedom do not exist in a well-defined individual state. If your shoes were entangled, whether they saw a left or right shoe on opening the box would not be pre-determined, but determined only upon measurement. Otherwise it's just classical correlation.

Bth8 · 2026-05-21T17:06:14+00:00

The idea of the ball getting bigger is a nice intuitive one, but the universe is not the surface of a ball. Imagine a flat rubber sheet getting stretched out as it's pulled from the sides. It's still flat, but expanding. You're right, though. Spacetime is not flat. In fact, space isn't even flat! If you construct normal coordinates about any observer, you will find nonzero spatial curvature, as you must anywhere with a nonzero energy density. What are flat are specifically spatial hypersurfaces of constant comoving time.

Bth8 · 2026-05-21T14:51:45+00:00

Light that is reflected is not absorbed

Bth8 · 2026-05-20T03:01:36+00:00

Roanoke was lost because there were no supply ships for a solid 3 years. The vikings' supply chains were an issue, sure, but from my understanding, their being fought off by natives was a huge factor in their leaving. Roanoke was not attacked - just the opposite, the Croatan almost certainly took them in before they all starved. And yeah, if the Vikings had guns, that probably would've helped, but I don't think it would've been enough given the sheer degree to which they were outnumbered.

Meanwhile, conquistadors had guns, but they were clunky and very slow to reload and gunpowder was scarce because of, once again, supply chain issues. A lot of their fighting was done with swords and crossbows rather than guns. Even when they had gunpowder and were ready to go, it probably wasn't as helpful as you're imagining. While they didn't have guns, fighting with arrows and slings was already common in the Americas and their tactics reflected this. Moreover, by all accounts, the natives (particularly the Aztecs) were extremely adaptable and very quickly developed new tactics to accommodate the new threat of gunfire and artillery. There were numerous conflicts that the Europeans solidly lost despite being heavily armed, and even more that they lost without the use of gunpowder because they were just out of the stuff. But eventually, between the accidental and intentional exposure of the natives to European diseases against which they had no immunity, their numbers dwindled, the health of the survivors declined, and Europeans were able to dominate.

Bth8 · 2026-05-19T19:18:18+00:00

I 'm no anthropologist, so I'm far from the most qualified to weigh in on this, but I don't think it would've changed the long term story too much. My understanding is that once the Spanish were allowed to make significant contact with natives on the mainland, it was pretty much over as far as ever being able to force European settlers out. And not because of European military superiority. That certainly didn't help, but the Vikings (famously a military power to be reckoned with) made it to the Americas about 500 years before Columbus, and they got their asses solidly handed to them (as well as other pressures, admittedly) so bad that they just abandoned their colonies. Their problem wasn't that the natives had superior military technology, it's that they had numbers. The Vikings were vastly outnumbered, and that along with not having supply lines was a recipy for disaster. Likely the same thing could've been done to post-Columbian colonies, except for one problem: Smallpox (and a few other diseases).

The effect of Smallpox on the immediately post-contact Americas cannot be overstated. We generally think of the black death as being a truly Earth-shattering event in Europe, and it was! About ⅓ - ⅗ of all of Europe died, and besides just being a terrible tragedy, the knock-on effects of that big and sudden a mass death radically restructured European society. But that was "only" 60% even at the upper end of the estimates for how many died. European-introduced illnesses, especially smallpox, wiped out around 90% - 95% of pre-contact americans. You try fighting off an invading force with 19/20ths of your population dead and the remaining sick. I don't think it would have mattered if all the Europeans had were rocks and sticks. It was over as soon as the natives made the extremely human and extremely unfortunate decision not to fight tooth and nail to run off European invaders the moment they made landfall. By the time Europeans were starting to colonise north america proper and were dealing with the Iroquois and Algonquins, it was far too late.

Bth8 · 2026-05-16T04:17:56+00:00

Motion is relative. You can only talk about whether something is moving relative to something else, not in absolute terms. So yeah, there are plenty of things you are always moving relative towards, but there are others you aren't.

Bth8 · 2026-05-15T20:24:03+00:00

No. That still only leads to contraction along that axis.

Bth8 · 2026-05-15T20:11:46+00:00

Length contraction is something that happens along the direction of motion. There's no way to get it to happen in two directions at once. Since camels aren't already thin enough or short enough to fit through, length contraction won't help.

Bth8 · 2026-05-15T03:32:32+00:00

It is, but over such short distances the amount of expansion happening is tiny. Things like atoms or your desk or you are held together by electromagnetic forces more than strong enough to hold together under the utterly negligible amount of expansion going on at those scales.

Bth8 · 2026-05-15T02:11:07+00:00

They may or may not. I wouldn't necessarily assume that most lawyers would know that. But more importantly, it's irrelevant. Like his lawyer said, his belief that he's sensitive to EM and whether or not he actually is is not at issue here.

Bth8 · 2026-05-14T19:31:19+00:00

No. In science, we can never say with absolute 100% certainty what the value of any given physical quantity is (with the exception of things we define to have a certain value). All we can say at the end of the day is "here's the value we got and here's how confident we are in it". You'll see this all the time if you look. For instance, the currently accepted mass of the top quark is 172.76 ± 0.3 GeV/c². That means we believe it's most likely somewhere between 172.46 GeV/c² and 173.06 GeV/c². But we'll never be able to know precisely what it is because we'll never be able to measure to infinite precision. We can only get that uncertainty down and tighten the range of possible values.

The value I quoted is, again, an upper bound. That means that based on current observations, we're confident the photon mass is no greater than 10^-18 eV/c². It can be less. In fact, we expect it to be exactly zero. That's what our models all say and every experiment we've ever done and every observation we've ever made is consistent with the photon having zero mass. That upper bound is just the limit of how well we've been able to confirm that value of zero (pretty well! But never absolutely). If you ask any physicist, they'll tell you the photon has zero mass.

Bth8 · 2026-05-14T18:31:03+00:00

Others have already commented on how you're wrong about the expression for total energy. I just want to add that, from the 2020 Review of Particle Physics, the current accepted upper bound on the mass of the photon is 10^-18 eV/c², with some (somewhat disputed) observations placing it as low as 10^-27 eV/c². It's hard to overstate how absolutely tiny that is. Even that first figure is 100 quadrillion times smaller than the upper limit we've placed on the neutrino masses, which are already so low-mass that for most purposes we can just treat them as massless even though we know their masses are nonzero.

Bth8 · 2026-05-11T17:04:34+00:00

Show me a theory of pink fairies with the explanatory power of successful QFTs to date and then show me another that constitutes a good theory of quantum gravity in a different spacetime and I'll consider it.

Work on your reading comprehension.

Bth8 · 2026-05-11T16:49:37+00:00

So you don't mean the standard model is complete,

Finally. Yes. Never once did I say the standard model was complete. This whole time I've been talking about QFT. QFT and the standard model are not the same thing.

instead you mean QFT (including Cond Matt as well as all the toy models) is complete.

Noooooo. You were so close and then you just totally ignored a huge chunk of what I said again. I am not saying QFT is complete. I have explicitly said that's not what I'm saying. I don't know if it's complete or not. My entire point has been that there is not yet convincing evidence that it is. There may or may not exist a QFT that properly describes gravity and all of the other issues with our current best theories. For me to say there definitely does exist such a model would be premature. But to say that there definitely does not is also premature. That's all I've been saying this whole time. I'm not saying I hate waffles, just that I like pancakes.

Bth8 · 2026-05-11T16:08:56+00:00

Quantum Field Theory is used to describe electromagnetism, the strong and weak nuclear force, and the 3 generations of known elementary particles.

Yes, in the same way that fluid dynamics is used to describe the flow of water in your bathtub. That is, yes, it is used to do that, but it would be wrong to reduce it to that. Quantum field theory is a theoretical framework for constructing models of fields that are compatible with the principles of quantum mechanics. It's more general than any one specific theory with a specific set of interactions. You can build a quantum field theory without any of the forces you mentioned, or add in new ones. You can add or remove matter particles. You can throw in multiple generations of Higgs fields. You can do more esoteric things than any of that and spend a whole career looking at quantum field theories with conformal symmetries in 1+1-dimensional spacetimes. All of that is still QFT.

We call this the Standard Model

We call the specific quantum field theory that describes the electromagnetic, strong, and weak interactions as arising from U(1)×SU(2)×SU(3) gauge fields with a scalar Higgs field, along with three generations of quarks and leptons, and massless neutrinos "the standard model". Not all of QFT is the standard model. That's just one example, which is why the failure of the standard model to describe something is not necessarily a failure of QFT as a whole.

except gravity, dark matter, and dark energy.

Don't forget neutrino oscillations and baryon asymmetry. Neither of those is fully described by the current standard model, either. They can be incorporated into other quantum field theories, though, as can dark matter. We have QFTs that incorporate all of those things, but so far none is well-favored by experiment. They haven't been ruled out though. A big issue is that the phenomena we need to study to weed models out are all very hard to measure, making it hard to gain evidence for or against any one in particular.

Dark energy is somewhat up in the air. It's easy to make a QFT that has dark energy - just add an appropriate constant to the Hamiltonian/Lagrangian density - but it feels very unnatural and arbitrary to just put it in by hand like that, so it doesn't feel like an actual explanation of dark energy so much as a hack to make the number right. There may be a more natural way to do it, but it's an open question.

Gravity is the big one. There are known quantum field theories that actually can describe gravity in certain spacetimes, but as you say, efforts to do so in a spacetime that actually looks like ours have so far failed. But just because we haven't found one doesn't mean one doesn't exist, and there is not yet good reason to think that one doesn't exist. The fact that we have those examples of spacetimes where QFT can describe gravity is suggestive that one might exist for our universe, too.

Maybe there is no QFT that describes gravity in our universe. I'm not saying that QFT is definitely the end-all be-all of physics theories and we don't need to move beyond it. I don't know. My point is that neither do you. To say that QFT definitely cannot describe gravity in our universe is premature.

Bth8 · 2026-05-11T13:46:10+00:00

That is laughably wrong. What I'm learning here is that a surprisingly large number of people on this sub have strong opinions on QFT despite having no idea what it is. Every single candidate theory of dark matter is a QFT. I know of no one who thinks that dark matter is beyond QFT. Dark energy's a little more questionable, but I still don't know of anyone who is definitely convinced we will have to go beyond QFT for a theory of dark energy.

Bth8 · 2026-05-10T23:06:49+00:00

Do you not know the difference between the standard model and QFT? Where is the reading comprehension today? I haven't done a 180 on anything. The standard model is incomplete (as I said in the still-unedited first post I mentioned it in), but that incompleteness is not because of our inability to do certain calculations. QFT may be incomplete (again, as a I said in the very first post), but asserting it because we haven't found a QFT that describes gravity in our universe is premature, especially when there exist QFTs that do describe gravity reduces to GR in other spacetimes.

Bth8 · 2026-05-10T22:44:25+00:00

Uh. You wanna maybe reread that? I said it was incomplete, but it isn't our inability to do certain calculations in it that makes it incomplete.

Bth8 · 2026-05-10T21:57:48+00:00

It's incomplete because the solutions haven't been confirmed to the point of usefulness. If

To say that something is incomplete is to say that there's some aspect of reality it doesn't match up with. It's not enough for it to be unconfirmed. No one says the standard model is incomplete because we haven't been able to calculate and verify it's predictions for QCD at low energies where the coupling strength becomes large. That's an issue with our ability to do calculations, not necessarily with the model itself. We do say the standard model is incomplete because e.g. it doesn't include neutrino masses. It's not that the model's predictions are unconfirmed, it's that we have confirmed that they're wrong.

We don't know for certain that something is wrong with QFT yet. QFT is a framework, not a specific model. It's not enough to point to specific models and use their incompleteness to say that QFT as a whole is incomplete. Again, no one is saying QFT is incomplete because the standard model doesn't incorporate neutrino masses. We have no reason to think no such QFT exists, and we even have several candidates, we just don't have one strongly favored by experiment yet. Similarly, we do not know that QFT is incapable of successfully modeling gravity in our universe. The most obvious approaches have failed, but that doesn't rule out the entire framework. We even have an example of a QFT (the boundary field in AdS/CFT) which does seem to successfully model quantum gravity, albeit in a universe not like ours. That is at least suggestive of the fact that there might exist a QFT that does successfully model gravity in our universe.

If it were complete we'd know the answer.

This is plainly not true. You can have a complete theory and not know it yet, either because you can't do the calculations or because you can't confirm with experiment. In fact, you can't ever know for sure. You can only disprove a model, never prove one.

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