sudoreboot

Tl;dr: Someone please explain to me why some physicists think something could ever cross the event horizon of a black hole.

There is a conflict between my understanding of what the event horizon of a black hole is vs the way that many theoretical physicists talk about them.

I understand that a result in general relativity is that time progresses more slowly in the presence of energy, and this is why light bends around massive objects.

The way I understand the dynamics around a black hole is that the surface of an event horizon is the region of space where the energy is so great that time literally grinds ~~to~~towards a halt (edit/clarification: from the perspective of an observer farther out). Light moves at the speed of causality, and when causality slows down, so does light. Light is bent and redshifted due to time dilation, and only when time stops does the wavelength of light go to zero. That's the event horizon as I understand it.

If an object falls towards a black hole, it shouldn't matter if we are that object or if we're just observing it from farther away, everyone should agree that it never crosses the boundary of the event horizon.

From a spectating observer's perspective, the object is redshifted until it fades entirely as it gradually stops moving through time (so light stops being emitted from it). But it will only ever approach the boundary asymptotically; it will never cross it.

~~From the perspective of the object itself, the universe around it will progressively speed up and the entirety of the history of the universe will play out behind it~~ (Edit: that only happens if the object accelerates to remain stationary). An infinite amount of time would pass everywhere else before it crosses the horizon. Now, that will never happen if black holes evaporate in finite time (and we have good reason to think they do). The black hole will evaporate long before any eternity passes anywhere. The more slowly you move through time, the faster this process will appear to you. When you are more or less frozen in time, the black hole will be evaporating at a rate that approaches 'instantaneously' - so the closer you get to it, the hotter it will appear and the faster it evaporates. You and everything else would literally radiate away from this noticeably shrinking event horizon before ever crossing it.

So, in this view, I feel utterly confused by physicists talking about "what it's like to cross the event horizon" or "what the interior of a black hole is like". Either my understanding is incorrect, or these physicists are just indulging themselves with hypotheticals rather than thinking about physics (or working on alternative models where black holes are fundamentally nothing like what I describe).

It's most likely me not understanding this properly, so.. what am I missing?

Update

As I mentioned in this comment, it has been shown that an event horizon may never form at all, and that all one ever sees is a shell of fading signatures followed by radiation from all the matter that falls into it.

I have more to learn about the particular dynamics around the area surrounding a black hole, but I believe I've managed to reduce my antecedents to the assumption that quantum information is conserved and the following counterfactuals, which appear promisingly independent of whichever dynamical model one might prefer:

1. A sufficiently long-lived asymptotic (sufficiently distant) observer would be able to identify a particular point in time at which a black hole will have fully evaporated.
2. A sufficiently long-lived asymptotic observer would be able to track the signature of something falling towards a black hole until it is radiated out.

Counterfactual (1) is supported by the prediction of Hawking radiation and means that the black hole has a finite life span. Counterfactual (2) is supported by the common claim that, to an observer far away, the wavelength of emitted light from an infalling object will go towards infinity as they get closer to the event horizon.

This means that the observer just has to wait long enough to detect each subsequent photon until the source of the emission has been radiated out, and so the observer is a witness of the fact that the infalling object was never inside the event horizon. For information to be conserved, there can never be disagreement between the objective experience of the witness and the information encoded in the radiation, and so if the infalling observer were to be reconstructed after being spat back out by the black hole, it would agree that it was never inside the horizon.

Feedback on my reasoning would be very welcome.

I think all of us here can agree that seeking to describe our universe in terms of laws and principles that allow us to make predictions about its dynamics is a worthy and fascinating pursuit. It is also undeniably valuable to any species that wishes to live and thrive in it.

However, us humans have developed this need to explain everything in terms of reasons for why things happen. What that means, exactly, varies between different contexts, but some interpretations are

• reasoned (practical or theoretic) justifications for actions taken by an agent;
• (primary) causes of events ("which of recent events was most necessary for this event to occur?");
• teleological purposes attributed to objects or events which explains their behaviours or occurrences (e.g. involving attractors in complex adaptive systems);
• sets of rules (dynamics) governing the evolution of systems which demonstrably gives rise to observed phenomena - the type of reasons most physicists are primarily concerned with.

There are a lot of finer distinctions to make - this was mostly off the top of my head. The point is: given any reason at all, one can always additionally demand a reason for that reason - but at which level in this hierarchy of explanations would you find the final, most fundamental and satisfactory explanation for why anything at all? Could such a level exist, or is the hierarchy infinite? Is the notion of what constitutes a 'reason' fundamentally anthropic, and is then requiring explanations for natural events a case of category error?

tl;dr: why, when and where is 42?

"Do you know how fast you were going?" asks the cop. "No," Heisenberg replies, "but I know precisely where I am!"

My partner ordered it for me a couple of weeks ago as a surprise, but she had to tell me shortly after because I was talking about it and she didn't want to risk me ordering it too. The anticipation has been torturous.

My partner and I are sharing our libraries with each other on both the Steam Deck and our desktop PCs, but the list of actually borrowed games constitutes only a fraction of our complete libraries. I would expect all (non-F2P) games to show up under either borrowed or excluded.

From searching around, it seems to be a recurring problem for various people, and it either spontaneously fixes itself or after deauthorising and reauthorising (some reporting they had to clear Steam's cache - which is the only thing I haven't tried yet because that would be a massive inconvenience). But I'm not finding a lot of solutions or answers to what the deal is.

Has anyone else dealt with this?

Edit: it looks as if the listed "borrowed" games are only those that have been actually played at some point, so it's possible the list isn't meant to be exhaustive. Doesn't explain the missing majority of games however.

Edit 2: I don't know if it was always the problem, but I just realised I had "show only ready to play games" selected, which obviously excludes all uninstalled games. I noticed because I tried downloading a game through the other account to see if that changed anything, and indeed it showed up. Mystery solved, hopefully.

(In a petty attempt at salvaging some dignity I want to add that I've had the problem of shared games not showing up before and I could swear this was not the problem...)

It's almost exclusively about USA right now and frankly I'm sick of this US-centrism.

You don't have to justify your fascination, but you are most welcome to!

'Proposed' includes old and new ideas alike. Consensus isn't a requirement either - it could be speculative, contentious or entirely uncontroversial, as long as it doesn't contradict what is currently known.

A place to discuss and share content about what may or may not be, and why it is so.

Natural Philosophy / !naturalphilosophy@slrpnk.net

This is one of my favourite episodes of Sean Carroll's Mindscape podcast. He talks about his recent work in attempting to derive the kind of spacetime geometry we observe from little more than the mere existence of a universal quantum wavefunction.

Shownotes:

I suspect most loyal Mindscape listeners have been exposed to the fact that I've written a new book, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime. As I release this episode on Monday 9 September 2019, the book will officially be released tomorrow, in print, e-book, and audio versions. To get in the mood, we've had several podcast episodes on quantum mechanics, but the "emergence of spacetime" aspect has been neglected. So today we have a solo podcast in which I explain a bit about the challenges of quantum gravity, how Many-Worlds provides the best framework for thinking about quantum gravity, and how entanglement could be the key to showing how a curved spacetime could emerge from a quantum wave function. All of this stuff is extremely speculative, but I'm excited about the central theme that we shouldn't be trying to "quantize gravity," but instead looking for gravity within quantum mechanics. The ideas here go pretty far, but hopefully they should be accessible to everyone.

Others are not broken, such as !twoxchromosomes@slrpnk.net. .

It's not a general functionality problem with subscribing or blocking. If you go to any thread in a community, the buttons work from there. It also works to sub from the community list.