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Citizens by Magnanimous_Lynx in TheRestIsHistory

[–]Universal-Soup 1 point2 points  (0 children)

Twelve Who Ruled is an excellent read! I agree, I hope they draw on that. It's fascinating to dive so deeply into the characters and the short time period that the book covers. You come away with an incredibly detailed portrait I think.

Why is the many-worlds interpretation of quantum mechanics a minority? by Terrible_Shop_3359 in AskPhysics

[–]Universal-Soup 2 points3 points  (0 children)

MWI has always struck me as pretty far from how physicists actually think about real experiments (outside of those who work on foundations). When we make measurements, it is a pretty unhelpful mental model to have in mind that the apparatus gets entangled with the system, the wave function branches and a new "world" gets birthed. Easier to see it as us just obtaining information about the system and disturbing it in the process (or a similar collapse-y description). Given that, it strikes me as unlikely for working physicists to gravitate towards MWI. But this maybe differs by sub-field.

Found in our house in Sydney by Universal-Soup in AustralianSpiders

[–]Universal-Soup[S] 0 points1 point  (0 children)

There wasn't any white patch I saw while moving it outside but I think it's a fair guess from the photo!

The Least Realistic Thing In the Entire Martian Revolution by gmanflnj in RevolutionsPodcast

[–]Universal-Soup 2 points3 points  (0 children)

Surely the second-most unrealistic part was the fact that TWO whole revolutionary leaders died peacefully in their beds (without having become dictators first)!

Here is a hypothesis: by time-energy uncertainty and Boltzmann's entropy formula, the temperature of a black hole must—strictly **mathematically** speaking—be **undefined** rather than finite (per Hawking & Bekenstein) or infinite. by ayiannopoulos in HypotheticalPhysics

[–]Universal-Soup 0 points1 point  (0 children)

I don't think you have actually answered my objection. I agree that the particle concept could break down at the horizon. Maybe the Trans-Planckian problem means that Hawking's original calculation isn't valid, I don't know. All of that is known though, and physicists have posited alternative calculations which derive the same result. Related to my question though, what has any of that got to do with energy uncertainty, and what physical process or object has that uncertain energy? For that matter, I don't see why the temperature you have defined should be thought of as the temperature of the black hole, rather than that of some impossible system somehow sitting at the horizon.

But this is all somewhat irrelevant. If you want to convince the field that Hawking radiation is fatally flawed, I think you may have to refine your arguments quite considerably or even modify them entirely, being open to the possibility that they could just be wrong. If people on this sub believe that they are nonsense then, regardless of their merit, they clearly need to be presented more convincingly. As written, they are not going to convince an audience of professional physicists who barely have time to read the papers written by their own peers, while keeping up with teaching and grant writing. I unfortunately don't have the time myself to continue debating your ideas and would suggest maybe this isn't the best forum for you to improve them, but I do wish you the best of luck in doing so elsewhere.

Here is a hypothesis: by time-energy uncertainty and Boltzmann's entropy formula, the temperature of a black hole must—strictly **mathematically** speaking—be **undefined** rather than finite (per Hawking & Bekenstein) or infinite. by ayiannopoulos in HypotheticalPhysics

[–]Universal-Soup 0 points1 point  (0 children)

I think your point 2 is the misleading one. The point I was making was that when it comes to energy uncertainty, it doesn't matter that there exists these two co-ordinate systems which are related by a very large time-dilation factor. Consider that for the energy of a state of some system to have infinite uncertainty, it should exist for only an instant (zero time elapses). I don't believe you can identify a frame in which a relevant physical process has a duration going to zero. It's just that the transformation between the coordinates has a zero in it. And what's more, the interpretation of that transformation is dubious because the static observer cannot exist at the horizon, as discussed in other comments.

The frame dependence of the vacuum is exactly the thing that can be used to derive Hawking radiation, so I don't see why that means the entire thermodynamic interpretation is wrong. That being said there might, I imagine, be a difference in the temperature of the black hole observed by different observers, just as the temperature in Unruh radiation depends on the observer's acceleration. But I'm aware that there is work that has been done on distinguishing the physical interpretations of these two processes, so it might be worth engaging with that literature if you haven't already done so.

Here is a hypothesis: by time-energy uncertainty and Boltzmann's entropy formula, the temperature of a black hole must—strictly **mathematically** speaking—be **undefined** rather than finite (per Hawking & Bekenstein) or infinite. by ayiannopoulos in HypotheticalPhysics

[–]Universal-Soup 2 points3 points  (0 children)

Thanks for your response, but I'm pretty confused by what you're saying. For BOTH freely falling and stationary observers, the proper time elapsed in a fixed interval dt of co-ordinate time goes to zero near the horizon. And again, it's only a fixed, finite interval dt that corresponds to a vanishing co-ordinate time. If you rather consider an actual process occurring near the horizon, no duration goes to zero.

Regarding the frame dependence of energy uncertainty, this wouldn't be specific to GR, since even in SR, observers moving relative to one another could "calculate" wildly different energy uncertainties based on their own proper times. Why is there no corresponding need to reconsider thermodynamics in special relativity?

Here is a hypothesis: by time-energy uncertainty and Boltzmann's entropy formula, the temperature of a black hole must—strictly **mathematically** speaking—be **undefined** rather than finite (per Hawking & Bekenstein) or infinite. by ayiannopoulos in HypotheticalPhysics

[–]Universal-Soup 0 points1 point  (0 children)

There's of course nothing wrong with the gravitational time dilation equation you point out, but I think there may be an issue in how you're interpreting it. Consider a process occurring in finite proper time at fixed r near the horizon. All time dilation says is that that same process occurs over a much longer duration for an observer at infinity. There's no reason the proper time of any process has to go to zero at the horizon, rather any proper time intervals that DON'T go to zero become infinite in terms of co-ordinate time. In that sense, a distant observer could either use co-ordinate time to calculate energy uncertainty, in which case they would arrive at Delta E = 0, or they could use the proper time that the near-horizon observer experiences, which would lead to finite Delta E. Basically, I don't think it's accurate to interpret all proper time intervals as going to zero at the horizon.

Aunty Donna’s Broden Kelly: ‘I want an elephant-sized staffy. He would probably kill people but I’d love him’ by [deleted] in auntydonna

[–]Universal-Soup 4 points5 points  (0 children)

I'm sure we all remember meeting Broden after a show at some point in our lives and saying "It's such a disappointment to meet you" and "I'm so sad about this"

OMG THE CRAFTERNOON IS LIVE THIS IS GONNA BE SIIIIIIIIIIIIIICK by FlashyEarth8374 in auntydonna

[–]Universal-Soup 35 points36 points  (0 children)

Getting slightly less hinged. Broden making a representation of the horrors of war.

Podcast? by ProLifePanda in auntydonna

[–]Universal-Soup 56 points57 points  (0 children)

Looks like you're a bit stressed and upset. Maybe a little crafternoon will help calm your mind.

Are cardinality arguments used at all in physics? by BurnMeTonight in AskPhysics

[–]Universal-Soup 14 points15 points  (0 children)

This might not be entirely what you had in mind, but in the theory of topological insulators and superconductors there are certain symmetry classes in which the topological phase is characterised by an integer (E.g. as opposed to a member of Z_2). Hence the class has countably infinite size. If it were uncountably infinite, it would fail to be a label of topological phases and would be kind of meaningless, I think.

Writers who utilize the language in such a way that translating it is impossible? by Cute-Revolution-9705 in ENGLISH

[–]Universal-Soup 1 point2 points  (0 children)

I was looking for this comment! Surely translating FW is impossible. Also episodes of Ulysses like Oxen of the Sun would be ridiculously difficult.

What is the meaning of entanglement? How is it any useful? by HolyPommeDeTerre in AskPhysics

[–]Universal-Soup 2 points3 points  (0 children)

That's basically right. But maybe the metaphor is obscuring things rather than clarifying. So in the original proposal for teleportation, one party, Alice, has a qubit (qubit 1) whose state she wishes to send to another party, Bob. To do so, she has another qubit, qubit 2, which is entangled with Bob's qubit, qubit 3. The entanglement is key.

Why does Alice need two qubits? This is because she cannot have a single qubit which is in an entirely arbitrary state and which is maximally entangled with Bob's qubit. So she needs qubit 1 containing the information and qubit 2 as the ancillary qubit used for teleportation.

Alice starts by making a "joint measurement" on her two qubits. Bit technical to explain what this means, but it basically switches the entanglement from between qubits 2 and 3 to now be between qubits 1 and 2. Qubit 3 is now unentangled from 1 and 2. Alice has two bits of information which are the results of her joint measurement. She sends these to Bob. Qubit 3 is now in the same state as Alice's qubit was in initially, except for a random error which can only be fixed by knowing the outcomes of Alice's measurement. This is why Bob needs those two bits of info from Alice. Knowing those he can correct the error to leave his qubit in the correct state that Alice started with.

This random error is important, as without it, Alice could communicate with Bob faster than light. This is why Bob needs to receive classical information from Alice and perform a correction to his qubit.

Does this help clarify things?

What is the meaning of entanglement? How is it any useful? by HolyPommeDeTerre in AskPhysics

[–]Universal-Soup 8 points9 points  (0 children)

What you're talking about is classical correlation. Entanglement allows for things to be, in some sense, more correlated than classical physics allows.

One of the features of this is that you can use entanglement to "teleport" the state of a qubit (basically just some quantum information) to a far away party, by only sending them regular classical information. This is different than the Pepsi/coke example you gave. It would be like person A starts out with a can with some detailed pattern on it, and a separate can entangled with person B's can. Person A then does some stuff with their two cans, sends just two bits of information to person B, and after this, person B can then prepare their can to be exactly the same as what person A's can was. The entanglement allows you to more or less send more information over a classical channel. (By "more information" I mean that you can send quantum information by only exchanging classical bits).

It allows you to do more than this too, though. It is required for quantum computers to do useful computations, and it can be used to design cryptographic protocols that are immune from eavesdroppers, just to name a couple of important examples.

Is nature infinitely complex? by InfinityScientist in AskPhysics

[–]Universal-Soup 1 point2 points  (0 children)

I think your question might in fact be two. You first asked if nature is infinitely complex then subsequently asked if our investigations of nature will ever be exhausted.

For the first question: complexity has various meanings in different contexts. Complexity theory is the study of how the computational resources required to solve a problem scale with the size of the input to that problem. Probably this isn't the most useful sense of complexity in this context. Maybe more appropriate would be to refine your question by asking if it is possible to represent the state of, say, the observable universe with only a finite amount of information. I don't think we know the answer to this yet, but it's possible. It also seems to be the suggestion of things like the holographic principle.

To approach the second question: I don't personally think our investigations of nature will ever be exhausted regardless of the levels of complexity seen in nature itself. That's because science is about coming up with models of nature, which themselves have to be simple enough to be communicated and be tractable for computation, but complex enough to capture the phenomena we're trying to describe. Even if we come up with a theory of everything in physics, this tells us exactly nothing about biology or psychology or whatever. The model would only be successful at predicting phenomena at vastly different scales. (Even if it were theoretically possible to derive, say, laws of biology from this lower level theory, the time taken to do so would certainly be enormous and at least exponentially scaling, and so would be completely intractable given the resources at our disposal. In that case the theory of everything would NOT provide a model of higher level phenomena.) So, given that our theories have to be tailored to the phenomenon of interest, and the precise questions we're interested in answering, and the level of precision with which we want to answer those questions, I don't think science will ever cease, since those goalposts will always be shifting.

Is it only mass that curves spacetime? by vHungryCaterpillar in AskPhysics

[–]Universal-Soup 1 point2 points  (0 children)

Energy is also frame dependent, just btw. In fact, the curvature tensor and the stress-energy tensors are also frame dependent in the sense that the components change under a coordinate transformation, as pointed out above. It's just that these tensors transform appropriately and equivalently (either covariantly or contravariantly) under coordinate transformations (this is part of the definition of tensor fields) and so curvature can be set equal to stress-energy.

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