Eventually everything will evaporate, not only black holes(ru.nl)
ru.nl
Eventually everything will evaporate, not only black holes
https://www.ru.nl/en/research/research-news/eventually-everything-will-evaporate-not-only-black-holes
55 comments
The work press-release-announced in the link at the top, the preprint for which is at <https://arxiv.org/abs/2305.18521>, has nothing to do with cosmic inflation. At all. The authors are at pains to contain the dynamical aspect of the spacetimes they investigate. In particular they write, "... we also expect our particle production mechanism to backreact on the spacetime. However, the spacetime background we have used here is constant by construction".
Their investigation works on asymptotically flat spacetimes and so (a) are manifestly not cosmological in itself and (b) can be "knitted" into a wide variety suitable comsological metrics by procedures like Israel-Darmois. Possibly including the (family of) cosmological spacetimes at the links you supplied. However...
I can't imagine even an exceptionally generous reading of only the link at the top (terse as it is) being relevant to any of the four in-English links you push in your comment. Those papers are particularly interested in background gravitational waves and the bulk expansion and contraction of space, all of which are a signature of a dynamical spacetime, quite the opposite of the background in the work at the top. The fifth, in Russian, focuses on black holes and neutron stars in but (a) in a dynamical spacetime and (b) not in a way that is (even trying to be generous) remotely related to the work discussed at the link at the top of the page. [However, I did note the 2021 Astrophysics Bulletin paper's authors' reference 38, which is Hawking's 1975 "Particle creations by black holes", and tried to take that one citation into account. It's raised in §2 around eqn (1) in the context of estimating a whole-universe distribution of black holes. Unfortunately this feels to me a bit like a conversation about laboratory mice swerving into commentary about quaking aspen groves being assessed as OK or not on the basis that both organisms share a distant common ancestor. The connection turns out to be less than tenuous.]
Lastly, I note via <https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...> that you have posted these links to HN at least twice before, and this is the second time they do not fit the context in a reasonable way. I don't think your repetitive posting is doing a service to anyone, including Н. Н. Горькавый and his coauthors.
Their investigation works on asymptotically flat spacetimes and so (a) are manifestly not cosmological in itself and (b) can be "knitted" into a wide variety suitable comsological metrics by procedures like Israel-Darmois. Possibly including the (family of) cosmological spacetimes at the links you supplied. However...
I can't imagine even an exceptionally generous reading of only the link at the top (terse as it is) being relevant to any of the four in-English links you push in your comment. Those papers are particularly interested in background gravitational waves and the bulk expansion and contraction of space, all of which are a signature of a dynamical spacetime, quite the opposite of the background in the work at the top. The fifth, in Russian, focuses on black holes and neutron stars in but (a) in a dynamical spacetime and (b) not in a way that is (even trying to be generous) remotely related to the work discussed at the link at the top of the page. [However, I did note the 2021 Astrophysics Bulletin paper's authors' reference 38, which is Hawking's 1975 "Particle creations by black holes", and tried to take that one citation into account. It's raised in §2 around eqn (1) in the context of estimating a whole-universe distribution of black holes. Unfortunately this feels to me a bit like a conversation about laboratory mice swerving into commentary about quaking aspen groves being assessed as OK or not on the basis that both organisms share a distant common ancestor. The connection turns out to be less than tenuous.]
Lastly, I note via <https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...> that you have posted these links to HN at least twice before, and this is the second time they do not fit the context in a reasonable way. I don't think your repetitive posting is doing a service to anyone, including Н. Н. Горькавый and his coauthors.
I disagree, 'everything will evaporate' assumes a model of one-time ever-expanding universe.
"Everything will evaporate" is the press-release title, and does not fairly capture the Schwarzschild-black-hole-focused work in the paper press-released by the university. The PR title overemphasizes and mischaracterizes the last paragraph of the paper's conclusion as something more than an appeal for further investigation of central masses other than black holes. Their analysis does not rely on the presence of a (particular family of) horizons (cf. Visser Phys. Rev. D 90, 127502 (2014)), and therefore other spherically symmetric non-rotating central masses (possibly even noncompact ones) might induce this gravitational analogue of the Schwinger effect.
> assumes ... ever-expanding universe
No it does not.
I already gave the link to the preprint in your parent comment, but for ease of access <https://arxiv.org/abs/2305.18521>. Equation (5) therein is the line element, standard Schwarzschild, and in particular you'll notice a lack of \Lambda or any other expansion term. I drew explicit attention to the asymptotic flatness and Israel-Darmois junction conditions in my comment you replied to.
We can "knit" (using junction conditions) an asymptotically flat solution into a cyclical spacetime like the Gorkavyi model in your set of links. Because the re-collapse timescales there are a lot shorter than the black hole era of the standard model, large black holes may not even stop accreting, but they will however still induce the gravitational pair production that is the topic of the paper. This seems at first glance to be comparable to the outgoing gravitational radiation induced by compact objects that Gorkavyi considers. If one takes the gravitational backreaction of the gravitational pair production idea into account, the incoming gravitational radiation might even make it and Gorkayvi roughly compatible (the idea being that it would induce a small acceleration on the BH similar to the "anti-gravity" idea raised in the appendix of his Astro. Bull. 76, 229-247, 2021 paper, contributing to the "Big Bounce"). A generalization of the Vaidya metric seems like it might be helpful. One might even wonder if there could be a gravitational analogue of the Stark effect induced upon close binaries (esp. with his relict neutron stars with large mass ratios) in a Gorkavyi cyclical model.
Unfortunately, since you engage with the title at the top and practically nothing else, you missed an opportunity for taking this type of synthesis seriously.
> assumes ... ever-expanding universe
No it does not.
I already gave the link to the preprint in your parent comment, but for ease of access <https://arxiv.org/abs/2305.18521>. Equation (5) therein is the line element, standard Schwarzschild, and in particular you'll notice a lack of \Lambda or any other expansion term. I drew explicit attention to the asymptotic flatness and Israel-Darmois junction conditions in my comment you replied to.
We can "knit" (using junction conditions) an asymptotically flat solution into a cyclical spacetime like the Gorkavyi model in your set of links. Because the re-collapse timescales there are a lot shorter than the black hole era of the standard model, large black holes may not even stop accreting, but they will however still induce the gravitational pair production that is the topic of the paper. This seems at first glance to be comparable to the outgoing gravitational radiation induced by compact objects that Gorkavyi considers. If one takes the gravitational backreaction of the gravitational pair production idea into account, the incoming gravitational radiation might even make it and Gorkayvi roughly compatible (the idea being that it would induce a small acceleration on the BH similar to the "anti-gravity" idea raised in the appendix of his Astro. Bull. 76, 229-247, 2021 paper, contributing to the "Big Bounce"). A generalization of the Vaidya metric seems like it might be helpful. One might even wonder if there could be a gravitational analogue of the Stark effect induced upon close binaries (esp. with his relict neutron stars with large mass ratios) in a Gorkavyi cyclical model.
Unfortunately, since you engage with the title at the top and practically nothing else, you missed an opportunity for taking this type of synthesis seriously.
I agree with your last point
Obligatory Last Question reference: https://users.ece.cmu.edu/~gamvrosi/thelastq.html
This stunning video / visualisation features the evaporation of everything. Ultimately everything cools to absolute zero. Time becomes meaningless.
Timelapse of the Future: A Journey to the End of Time
https://www.youtube.com/watch?v=uD4izuDMUQA
edit: discussed previously here: https://news.ycombinator.com/item?id=33046171
Timelapse of the Future: A Journey to the End of Time
https://www.youtube.com/watch?v=uD4izuDMUQA
edit: discussed previously here: https://news.ycombinator.com/item?id=33046171
Things still happen in heat death because of quantum mechanics and fluctuations. Time still has a meaning, but it may lose its arrow if microscopic quantum interactions are what dominates. At a small scale, these have no direction in time. The direction is macroscopic.
My favorite semi related video on this is Susskind’s: Why is time a one way street? https://www.youtube.com/watch?v=jhnKBKZvb_U&t=600s (YouTube) It’s a one way street because the multiverse makes observer moments like ours (ones not in heat death like Boltzmann brains) a common state of affairs. That is unachievable in our universe because of infinite heat death. Something must exist outside of our universe (other universes) to offset the future of our universe where Boltzmann brains will dominate the class of observers. If infinite in time heat death with fluctuations is our universe’s fate, that we are not Boltzmann brains is secured by a multiverse which makes many more universes not in heat death which outpace the ones in heat death. Yes BB’s really are a problem to modern physics/cosmology, and one way out is a multiverse where many many more universes are spawned (and non-degenerate ones) by the time one is in heat death.
My favorite semi related video on this is Susskind’s: Why is time a one way street? https://www.youtube.com/watch?v=jhnKBKZvb_U&t=600s (YouTube) It’s a one way street because the multiverse makes observer moments like ours (ones not in heat death like Boltzmann brains) a common state of affairs. That is unachievable in our universe because of infinite heat death. Something must exist outside of our universe (other universes) to offset the future of our universe where Boltzmann brains will dominate the class of observers. If infinite in time heat death with fluctuations is our universe’s fate, that we are not Boltzmann brains is secured by a multiverse which makes many more universes not in heat death which outpace the ones in heat death. Yes BB’s really are a problem to modern physics/cosmology, and one way out is a multiverse where many many more universes are spawned (and non-degenerate ones) by the time one is in heat death.
> BB's really are a problem to modern physics/cosmology
No, they really aren't. They have never been observed. They are incompatible with present-day observations, and so as far as we can tell probably they have never existed in the history of our observable universe. They thus are a diagnostic on approaches to cosmology which have conditions favourable to BBs in approximately present times (or in the past), essentially killing any theory that does not suppress them.
They also imperil some theories of the far future which rely on fluctuation theory to produce a whole new universe (some decay-of-false-vacuum models, for instance). Very short lived and spatially tiny low-entropy configurations are enormously enormously ENORMOUSLY more likely than large low-entropy configuration that persist. Boltzmann brains describe a very short lived (much less than seconds) fluctuation into a very low entropy configuration, and are thus much more likely than a fluctuation producing Boltzmann being who can survive in outer space for at least minutes, let alone a galaxy in which a thinking being evolved and personally experienced many years of life, or a universe with many such galaxies.
This also means that because of the scale and history of the universe that we have direct experience of, one cannot safely draw a physical-theory parallel between our universe's projected high-entropy far future and our low-entropy past more distant than the dense low-entropy phases about which we have evidence (from the surface of last scattering to baryon species and abundances, ...).
Multiverses are not needed in this analysis, and don't really help one way or another. If you figure out how some other space in a multiverse configuration interacts with ours (and prove it experimentally or observationally), you will have mostly just changed our understanding of our universe and its (quasi-)local physics, particularly thermodynamics.
No, they really aren't. They have never been observed. They are incompatible with present-day observations, and so as far as we can tell probably they have never existed in the history of our observable universe. They thus are a diagnostic on approaches to cosmology which have conditions favourable to BBs in approximately present times (or in the past), essentially killing any theory that does not suppress them.
They also imperil some theories of the far future which rely on fluctuation theory to produce a whole new universe (some decay-of-false-vacuum models, for instance). Very short lived and spatially tiny low-entropy configurations are enormously enormously ENORMOUSLY more likely than large low-entropy configuration that persist. Boltzmann brains describe a very short lived (much less than seconds) fluctuation into a very low entropy configuration, and are thus much more likely than a fluctuation producing Boltzmann being who can survive in outer space for at least minutes, let alone a galaxy in which a thinking being evolved and personally experienced many years of life, or a universe with many such galaxies.
This also means that because of the scale and history of the universe that we have direct experience of, one cannot safely draw a physical-theory parallel between our universe's projected high-entropy far future and our low-entropy past more distant than the dense low-entropy phases about which we have evidence (from the surface of last scattering to baryon species and abundances, ...).
Multiverses are not needed in this analysis, and don't really help one way or another. If you figure out how some other space in a multiverse configuration interacts with ours (and prove it experimentally or observationally), you will have mostly just changed our understanding of our universe and its (quasi-)local physics, particularly thermodynamics.
Just because whole new universes might fluctuate from spacetime patches, doesn't mean the non-fluctuating patches wont be in heat death forever in the far future.
In so far as we can talk about multiple universes in such a picture, "ours" will be in heat death and some daughter spacetimes will not be for some duration.
To say we can't predict more than 14b.y. in to the future seems at odds with most theoreticians and I've seen many predict much further with mainstream theories.
For BBs, yes the "tiny" ones will be exponentially more likely. But it seems like the 'medium to large' BBs in the heat death spacetimes will outnumber natural observers still, unless there are more spacetimes out of heat death comparatively. Some kind of measure of pre-heat death spacetimes vs far-into heat death spacetimes is needed to theoretically match our observation of no BBs. This is a multiverse.
A certain kind of multiverse does this, one where the odds to fluctuate new universes is high enough to outpace the ones in terminal heat death. I mean, we talk about inflation with little hope of the verification you talk about in your last paragraph. This is barely anything beyond inflation, it just sets the proper measure/odds among all the details to match observations. To say it does nothing, what of Susskind's video then? I'm just paraphrasing him. Carroll and Susskind both find it useful to talk of BB's, and use them to weigh on which theories to accept. That's all I was saying. Whether one has actually existed, don't know. Inflation might be so pervasive it makes BBs infinitesimal.
In so far as we can talk about multiple universes in such a picture, "ours" will be in heat death and some daughter spacetimes will not be for some duration.
To say we can't predict more than 14b.y. in to the future seems at odds with most theoreticians and I've seen many predict much further with mainstream theories.
For BBs, yes the "tiny" ones will be exponentially more likely. But it seems like the 'medium to large' BBs in the heat death spacetimes will outnumber natural observers still, unless there are more spacetimes out of heat death comparatively. Some kind of measure of pre-heat death spacetimes vs far-into heat death spacetimes is needed to theoretically match our observation of no BBs. This is a multiverse.
A certain kind of multiverse does this, one where the odds to fluctuate new universes is high enough to outpace the ones in terminal heat death. I mean, we talk about inflation with little hope of the verification you talk about in your last paragraph. This is barely anything beyond inflation, it just sets the proper measure/odds among all the details to match observations. To say it does nothing, what of Susskind's video then? I'm just paraphrasing him. Carroll and Susskind both find it useful to talk of BB's, and use them to weigh on which theories to accept. That's all I was saying. Whether one has actually existed, don't know. Inflation might be so pervasive it makes BBs infinitesimal.
Sorry, assume I've read standard textbooks and Ellis-Maartens-Mccallum, and explain to me how inflation controls the spatially flat FLRW chart density of low-entropy fluctuations in the quasi de Sitter +CC phase (ideally beginning with the "dark era", or even the earlier black hole era if you want to deal in nonequilibrium entropy explicitly, rather than just assuming heat death).
(I don't know where you got "14b.y." from; we still have the local group (including Milkdromeda) making new stars that soon from now; it's a cosmological eyeblink).
> This is barely anything beyond inflation, it just sets the proper measure/odds among the details to match observations
"Barely anything" seems to be doing a lot of heavy lifting there, but perhaps I'm missing something simple. See at the end below.
> For BBs, yes the "tiny" ones will be exponentially more likely.
Well, yes, statmech.
The problem is that if you allow non-"tiny" low entropy states you get them even during the matter-dominated era, so our sky should be sufficiently full of Boltzmann-russell-teapots to show up in studies of high-redshift quasars (and H II).
I do not understand the rest of that paragraph.
> That's all I was saying.
If that was all you were saying, I'd agree. I used the word "diagnostic" in the comment you replied to. But you also write:
> Inflation might be so pervasive it makes BBs infinitesimal
???
> ... Susskind ...
Are you trying to summarize stochastic eternal inflation? Or is this something out of his recent investigations of Sachdev-Ye-Kitaev? I haven't looked at his DSSYK stuff because AdS results aren't interesting to me.
ETA (just for me, i had to put this somewhere to find it later): Brandenberger et al 1992 "The Entropy of the Gravitational Field", https://arxiv.org/abs/gr-qc/9208009v1
(I don't know where you got "14b.y." from; we still have the local group (including Milkdromeda) making new stars that soon from now; it's a cosmological eyeblink).
> This is barely anything beyond inflation, it just sets the proper measure/odds among the details to match observations
"Barely anything" seems to be doing a lot of heavy lifting there, but perhaps I'm missing something simple. See at the end below.
> For BBs, yes the "tiny" ones will be exponentially more likely.
Well, yes, statmech.
The problem is that if you allow non-"tiny" low entropy states you get them even during the matter-dominated era, so our sky should be sufficiently full of Boltzmann-russell-teapots to show up in studies of high-redshift quasars (and H II).
I do not understand the rest of that paragraph.
> That's all I was saying.
If that was all you were saying, I'd agree. I used the word "diagnostic" in the comment you replied to. But you also write:
> Inflation might be so pervasive it makes BBs infinitesimal
???
> ... Susskind ...
Are you trying to summarize stochastic eternal inflation? Or is this something out of his recent investigations of Sachdev-Ye-Kitaev? I haven't looked at his DSSYK stuff because AdS results aren't interesting to me.
ETA (just for me, i had to put this somewhere to find it later): Brandenberger et al 1992 "The Entropy of the Gravitational Field", https://arxiv.org/abs/gr-qc/9208009v1
https://en.wikipedia.org/wiki/Conformal_cyclic_cosmology
If everything but what exists at the quantum level then CCC is a possibility.
If everything but what exists at the quantum level then CCC is a possibility.
I’m petty sure this is loosely agreed by Susskind except CCC is a more specific version. Entire bubble universes have a chance to fluctuate out of any patch of spacetime. (Colemann-Delucca process or something). That fractal nature of spacetime is appealed to by Susskind in the video.
Sean Carroll disagrees wrt Boltzmann brains will dominate the class of observers.
https://youtu.be/nqQrGk7Vzd4?t=2614
https://youtu.be/nqQrGk7Vzd4?t=2614
That’s because he disagrees with mainstream cosmology models in a different way than Susskind. Susskind takes the cosmology of our bubble universe as more settled, but addendums a huge inflationary multiverse on top. I’m pretty sure Carroll disagrees with the cosmology model of our bubble universe, and uses that to rule out BB’s dominating instead. Susskind’s says BB’s dominate any single universe over time, but not the multiverse as a whole.
There's also the branches of our multiverse where we simply don't experience heat death due to being on the unlikely side of the 2nd law of thermodynamics. Infinite simulations in those branches could account for a lot of "normal" experience. I haven't done the math but it seems intuitively like a simulation that keeps running in 10^-M branches (effectively quantum immortality) due to avoidance of entropy increase are more frequent than the 10^-N occurrence of boltzman brains where N>>M.
Given that decoherence is not perfect, I'd expect those branches to lack the "normal" macroscopic structure and maybe the time arrow as they interfere with each other.
Melodysheep in general is just amazing, both for the Symphony of Science remixes (and film/TV ones) and the more recent science-y videos.
The Museum of Alien Life is stunning and reminds me of a sci-fi Encarta MindMaze.
https://youtube.com/watch?v=ThDYazipjSI
The Museum of Alien Life is stunning and reminds me of a sci-fi Encarta MindMaze.
https://youtube.com/watch?v=ThDYazipjSI
There’s also one of MetaBallStudios perspective comparisons. They usually get recommended for less serious videos, but this one is something else: https://youtube.com/watch?v=Zb5qTdb6LbM
This reminds me of Wikipedia's Timeline of the Far Future (and they do mean far).
[0]: https://en.wikipedia.org/wiki/Timeline_of_the_far_future
[0]: https://en.wikipedia.org/wiki/Timeline_of_the_far_future
Super interesting. This far future allows for highly improbable events to occure, like the formation of Boltzmann brains.
https://en.wikipedia.org/wiki/Boltzmann_brain
> "Around this vast timeframe, quantum tunnelling in any isolated patch of the universe could generate new inflationary events, resulting in new Big Bangs giving birth to new universes."
it's ok guys we will get new universes
it's ok guys we will get new universes
That will take 10^10^10^56 years.
There are about 10^50 atoms on earth, and about about 10^82 atoms in the observable universe. There aren't nearly enough atoms in the universe to store the number written out in full.
1/10: terrible delivery time.
There are about 10^50 atoms on earth, and about about 10^82 atoms in the observable universe. There aren't nearly enough atoms in the universe to store the number written out in full.
1/10: terrible delivery time.
eventually the universe becomes so empty that there is nothing that can actually change so time becomes meaningless.
i'm not an expert in inflationary events but i assume they would be outside of our 'light cone' anyway
So not only will delivery take forever it will also be delivered at the wrong address? Seems like some things will never change...
... and when it finally arrives, the box will be empty. :-)
The universe is a funny mix of the ultimate free lunch and just getting reamed by entropy and expansion. I wish it would make up its mind.
The universe is a funny mix of the ultimate free lunch and just getting reamed by entropy and expansion. I wish it would make up its mind.
What a fascinating document!
I understand only bits and pieces bit it’s weirdly satisfying nonetheless.
I discovered it in 2020 when it seemed the world really was falling apart, and agree that it was strangely calming to think about such huge timescales.
Cool to see Radboud university on the front page. It was my alma mater for both my bachelor‘s and master‘s degrees.
I have to assume through some form of leptogensis or similar that we could engineer our galaxies or maybe entire universe so that this feature is at least delayed much longer, if not avoided entirely
We have no clue what is going to happen in billions of years. We are just extrapolating some known local parameters over a time span we can't directly observe.
A fundamental premise of physics and cosmology is that the universe is consistent.
Unlike prescientific beliefs which held that the celestial sphere was comprised of some non-earthly material (in some conceptualisations, a quintessence or fifth element), what current astronomical observation, and both theoretical and applied physics show is that the laws and substance of the universe are consistent so far as we can observe. Well, aside from that pesky dark matter and dark energy stuff ...
... but the things we can see and detect ... show normal matter, mostly hydrogen, some helium, a bit of lithium, and a smattering of heavier elements in supernovae and neutron-star explosions, with gravity and light behaving as they do locally (again: relativistic effects notwithstanding).
To argue that things we cannot observe might (or more strongly, do) behave differently ... is to argue on the basis of ignorance. That might be interesting, but it isn't scientific, in the sense of knowledge based on empirical observation and theory derived therefrom.
Yes, at extreme extents, especially of time, things become uncertain. But we do the best we can.
Over the past 150 years, human understanding of the greater universe has progressed profoundly. In the 1870s, the Earth and Sun were believed to be perhaps a few millions to hundreds of millions of years old, with extant theories failing to account for the observed energies of the overall system in a consistent way. The Universe was the Milky Way, other galaxies didn't exist. We've since determined the age of the Earth to within a few tens of millions of years, that there are galaxies beyond our own, and with present tools (including the James Webb Infrared Space Telescope) can look back to very nearly the practical limits of visual observation of the Universe. And we can see what stuff is made of, how fast it is moving relative to us, and how massive it is.
The notion of truth values about future events has always confounded philosophy and epistemics. There is the problem of future contingents ("there will be a sea battle tomorrow"), or in the case of the cosmology of the far future, noncontingent futures (the ultimate outcome won't depend on our own actions), whose states we'll never be able to directly observe. The only guide we ultimately have is the presumption of consistency.
Unlike prescientific beliefs which held that the celestial sphere was comprised of some non-earthly material (in some conceptualisations, a quintessence or fifth element), what current astronomical observation, and both theoretical and applied physics show is that the laws and substance of the universe are consistent so far as we can observe. Well, aside from that pesky dark matter and dark energy stuff ...
... but the things we can see and detect ... show normal matter, mostly hydrogen, some helium, a bit of lithium, and a smattering of heavier elements in supernovae and neutron-star explosions, with gravity and light behaving as they do locally (again: relativistic effects notwithstanding).
To argue that things we cannot observe might (or more strongly, do) behave differently ... is to argue on the basis of ignorance. That might be interesting, but it isn't scientific, in the sense of knowledge based on empirical observation and theory derived therefrom.
Yes, at extreme extents, especially of time, things become uncertain. But we do the best we can.
Over the past 150 years, human understanding of the greater universe has progressed profoundly. In the 1870s, the Earth and Sun were believed to be perhaps a few millions to hundreds of millions of years old, with extant theories failing to account for the observed energies of the overall system in a consistent way. The Universe was the Milky Way, other galaxies didn't exist. We've since determined the age of the Earth to within a few tens of millions of years, that there are galaxies beyond our own, and with present tools (including the James Webb Infrared Space Telescope) can look back to very nearly the practical limits of visual observation of the Universe. And we can see what stuff is made of, how fast it is moving relative to us, and how massive it is.
The notion of truth values about future events has always confounded philosophy and epistemics. There is the problem of future contingents ("there will be a sea battle tomorrow"), or in the case of the cosmology of the far future, noncontingent futures (the ultimate outcome won't depend on our own actions), whose states we'll never be able to directly observe. The only guide we ultimately have is the presumption of consistency.
Well nevermind the unknown unknowns. There are even known unknowns, like quantum gravity. Like yeah it's fun to speculate what will happen billions of years from now, but with many known gaps in physical theories, it's quite possible or even likely that our current prediction will have to undergo significant revision.
True (a known known), but ...
... one of my broader and highly significant points reponding to treprinum is that models of the future beyond our ability to actually witness them are a fraught epistemic space.
Of the various definitions of "science" is Popper's notion of falsifiability. There are numerous criticisms of that criterion, and the one I'm highlighting here is that we cannot falsify that which we will never witness.
It's tough enough to make a prediction about the next five minutes, tomorrow, week, month, or year. The span of a human lifetime (or adult awareness) spans roughly 50--100 years. The span of a given civilisation or culture anywhere from roughly a century to a few millennia. Of civilisation, ten millennia, of modern humans, roughly 100--200 millennia, of humans as a species, about 2 million years.
You and I will in all probability not be here to witness what will occur in the year 2123 (and quite probably much sooner, even given a long life). There are predictions which exist for what will transpire in that timespan, but our touchstone for judging these is largely based on what we have observed in the past, in various domains (astronomy, geology, climate, biology, ecology, social sciences, history, humanities). But in the sense that we can make and test a prediction ... we're sort of up a creek.
I'll go out on a limb (and emphasize the point again) that consistency is our only guide.
... one of my broader and highly significant points reponding to treprinum is that models of the future beyond our ability to actually witness them are a fraught epistemic space.
Of the various definitions of "science" is Popper's notion of falsifiability. There are numerous criticisms of that criterion, and the one I'm highlighting here is that we cannot falsify that which we will never witness.
It's tough enough to make a prediction about the next five minutes, tomorrow, week, month, or year. The span of a human lifetime (or adult awareness) spans roughly 50--100 years. The span of a given civilisation or culture anywhere from roughly a century to a few millennia. Of civilisation, ten millennia, of modern humans, roughly 100--200 millennia, of humans as a species, about 2 million years.
You and I will in all probability not be here to witness what will occur in the year 2123 (and quite probably much sooner, even given a long life). There are predictions which exist for what will transpire in that timespan, but our touchstone for judging these is largely based on what we have observed in the past, in various domains (astronomy, geology, climate, biology, ecology, social sciences, history, humanities). But in the sense that we can make and test a prediction ... we're sort of up a creek.
I'll go out on a limb (and emphasize the point again) that consistency is our only guide.
That’s what we get for living in a giant explosion. Who thought this was a good idea?
Wasn't it widely regarded as a bad move?
I thought that was coming down from the trees? And didn't some people think even the trees were a mistake?
I believe they're referring to Hitchhiker's Guide to the Galaxy. It's kind of an iconic line for those who have read it because of how it sets the tone of the book: "In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move."
https://www.goodreads.com/quotes/1-the-story-so-far-in-the-b...
https://www.goodreads.com/quotes/1-the-story-so-far-in-the-b...
Parent comment is also referencing HGTTG. Right at the beginning, in fact:
"Many were increasingly of the opinion that they'd all made a big mistake coming down from the trees in the first place, and some said that even the trees had been a bad move, and that no-one should ever have left the oceans."
"Many were increasingly of the opinion that they'd all made a big mistake coming down from the trees in the first place, and some said that even the trees had been a bad move, and that no-one should ever have left the oceans."
Right? Feels like there has to be a better way to do this
That one requires getting it right at the first time, unlike this one.
Sounds like Mahapralaya in Hinduism. It means the great dissolution where the universe dissolves back into... whatever you want to call it. Hindus call it God but you could equally think of it as nothingness.
What? So we not coming back, it will be forever? It’s cool that think about what forever feels like after we are gone
Here's a link to the actual paper, which for some reason this press release neglected to link.
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.13...
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.13...
Unless we can control it the black holes at that time.
I don't understand this explanation of Hawkins radiation:
> A particle and its anti-particle are created very briefly from the quantum field, after which they immediately annihilate. But sometimes a particle falls into the black hole, and then the other particle can escape
Is it not equally likely that an anti particle falls into the black hole than a normal particle? Why is there evaporation?
> A particle and its anti-particle are created very briefly from the quantum field, after which they immediately annihilate. But sometimes a particle falls into the black hole, and then the other particle can escape
Is it not equally likely that an anti particle falls into the black hole than a normal particle? Why is there evaporation?
That's the popular explanation, and yes, it's incorrect.
What's really going on is more deeply rooted in some esoterica of General Relativity, where it does make sense. I don't pretend to understand it.
What's really going on is more deeply rooted in some esoterica of General Relativity, where it does make sense. I don't pretend to understand it.
It's not that the in-falling particle is an anti-particle which annihilates with a particle inside the black hole. There are no particles inside the black hole, in theory, it's just a singularity. Instead it's that when one of the particle escapes, whether it's antimatter or not, the energy of that spontaneously created particle must be balanced out somewhere (conservation of energy), and that balance comes from the black hole.
The press release at the top is very thin. There is a better summary and discussion at <https://bigthink.com/starts-with-a-bang/hawking-radiation-bl...>.
> Is it not equally likely that an anti particle falls into the black hole than a normal particle?
A photon is its own antiparticle. If a pair of photons is produced via a mechanism similar to the one in the paper from the press-release at the top then each can develop a very different trajectory from the other.
Conversely, an electron and a positron are each other's anti-particle. They have the same invariant mass. If they are formed as a pair, they can quickly annihilate (being electrically attracted to one another), or may in some cases separate (e.g. because of immersion in an electric field, as discussed in the paper and the summary of it by Ethan Siegel at the bigthink link above). A question then arises: if the Schwinger effect means a strong electric field can separate a positron-electron pair that pops into existence (taking energy from the electric field), can a strong gravitational field also separate them (taking energy from the gravitational field)? That's essentially what the paper explores, but using a simple electrically uncharged, massive, minimally-interacting scalar particle field for ease of calculation.
The model particle does not self-attract nor self-repel and does not require assessment of collinear momentum, particle decays, bound states, (inverse) Compton scattering, and so forth. The particles and antiparticles are indistinguishable; they just happen to pop up in correlated pairs. The trajectory of each half of the pair is freer to evolve in a gravitational field than for Standard Model physics (which has much stronger interactions than gravitation), but the simplified model plausibly translates to qualitatively similar results for real particles as we know them.
So, because there's no difference between the particle and the anti-particle (crucially the masses are identical) it doesn't matter which one goes which way. The argument in the paper for black holes (and other compact masses) is that some fraction of particles will fall inwards and some will escape to infinity, and the fraction is mostly determined by distance from the large central mass.
There is evaporation because the pairs pop up outside the black hole because its dynamical spacetime creates the equivalent of an acceleration (accelerations generally produce differences in particle-counts; the no-particle vacuum of an observer can be full of particles for an accelerated observer). Causing a particle-pair to appear outside it has reduces total mass of the black hole ("gravitational backreaction"). Hawking (and this paper) feed a fraction of the particles back into a black hole to make the spacetime less dynamic (in particular keeping the black hole mass constant), for ease of calculation.
The paper however goes further and generalizes the mechanism to any gravitating mass, not just black holes. A less-compact mass with no horizon (e.g. a neutron star) also causes particle pairs to pop up around it, and some fraction of those particles will fall onto the surface of the object as a reasonable proxy for a more technical treatment of gravitational backreaction. Many particles may hover around in the area like a very thin and very cold atmosphere. Others may escape to infinity.
> Is it not equally likely that an anti particle falls into the black hole than a normal particle?
A photon is its own antiparticle. If a pair of photons is produced via a mechanism similar to the one in the paper from the press-release at the top then each can develop a very different trajectory from the other.
Conversely, an electron and a positron are each other's anti-particle. They have the same invariant mass. If they are formed as a pair, they can quickly annihilate (being electrically attracted to one another), or may in some cases separate (e.g. because of immersion in an electric field, as discussed in the paper and the summary of it by Ethan Siegel at the bigthink link above). A question then arises: if the Schwinger effect means a strong electric field can separate a positron-electron pair that pops into existence (taking energy from the electric field), can a strong gravitational field also separate them (taking energy from the gravitational field)? That's essentially what the paper explores, but using a simple electrically uncharged, massive, minimally-interacting scalar particle field for ease of calculation.
The model particle does not self-attract nor self-repel and does not require assessment of collinear momentum, particle decays, bound states, (inverse) Compton scattering, and so forth. The particles and antiparticles are indistinguishable; they just happen to pop up in correlated pairs. The trajectory of each half of the pair is freer to evolve in a gravitational field than for Standard Model physics (which has much stronger interactions than gravitation), but the simplified model plausibly translates to qualitatively similar results for real particles as we know them.
So, because there's no difference between the particle and the anti-particle (crucially the masses are identical) it doesn't matter which one goes which way. The argument in the paper for black holes (and other compact masses) is that some fraction of particles will fall inwards and some will escape to infinity, and the fraction is mostly determined by distance from the large central mass.
There is evaporation because the pairs pop up outside the black hole because its dynamical spacetime creates the equivalent of an acceleration (accelerations generally produce differences in particle-counts; the no-particle vacuum of an observer can be full of particles for an accelerated observer). Causing a particle-pair to appear outside it has reduces total mass of the black hole ("gravitational backreaction"). Hawking (and this paper) feed a fraction of the particles back into a black hole to make the spacetime less dynamic (in particular keeping the black hole mass constant), for ease of calculation.
The paper however goes further and generalizes the mechanism to any gravitating mass, not just black holes. A less-compact mass with no horizon (e.g. a neutron star) also causes particle pairs to pop up around it, and some fraction of those particles will fall onto the surface of the object as a reasonable proxy for a more technical treatment of gravitational backreaction. Many particles may hover around in the area like a very thin and very cold atmosphere. Others may escape to infinity.
I prefer (and submitted) the summary of this work at https://bigthink.com/starts-with-a-bang/hawking-radiation-bl... which also has the advantage of linking to the arxiv preprint https://arxiv.org/abs/2305.18521 unlike this terse and not-very-enlightening press release by the authors' institution.
However, cyclical cosmology model recently got a good theoretical basis in the works of Nick Gorkavyi. He found a mechanism for expansion-collapse cycles that is purely based on General Relativity without any quantum gravity theory.
If you are interested, here are the papers:
https://pos.sissa.it/335/039/
https://academic.oup.com/mnras/article/476/1/1384/4848298
https://academic.oup.com/mnras/article/461/3/2929/2608669
https://arxiv.org/abs/2110.10218
https://www.sao.ru/Doc-k8/Science/Public/Bulletin/Vol76/N3/A...