An alternate hypothesis which seems equally interesting, albeit for different reasons, is at the end of the article:
> Another explanation for why the JWST may have seen an overrepresentation of galaxies rotating in one direction is that the Milky Way's own rotation could have caused it.
> Previously, scientists had considered the speed of our galaxy's rotation to be too slow to have a non-negligible impact on observations made by the JWST.
> “If that is indeed the case, we will need to re-calibrate our distance measurements for the deep universe," Shamir concluded. "The re-calibration of distance measurements can also explain several other unsolved questions in cosmology such as the differences in the expansion rates of the universe and the large galaxies that according to the existing distance measurements are expected to be older than the universe itself."
perihelions 2 days ago [-]
I'm utterly confused what's going on. They're measuring galaxies' rotations by looking at images of the subset that are spiral galaxies, and checking which direction the arms spiral. They describe their image processing algorithm in their paper [0]. (it's around figure 3)
How can local movement of stars within the Milky Way affect which way spiral galaxy arms are pointing?
You cannot decide galaxy rotation by looking at it. Consider this gallaxy:
_______
\ _ B\
/ /_\ \
\ \_/ \
\A____ /
\/
Is A side closer to us, or is B side closer to us? You can't tell by just looking at it, if the B is closer that we are seeing bottom of the galaxy and it rotates CW. If A is closer than we are seing top of the gallaxy and it rotates CCW.
AstralStorm 2 days ago [-]
Yes you can, by gravitational lensing of another body. Works exactly by triangulation in Lorentz space. You can thank Einstein for this feature of special relativity.
(Tricky part is deciding it's another body from a picture. You would need a second JWST preferably far in the other Lagrange point. Stereoscopy solves it directly. You can )
The thing is, you need another galaxy in the way to be sure, or a black hole. Theoretically our Sun can serve. [] Or the supermassive black hole in the center of our galaxy, but the sensitivity might be a bit compromised.
There is no absolute direction for a galaxy’s spin—it’s always relative to the observer’s perspective.
So I’d suspect they’re saying time and distance would need to be factored in rather than just looking at static images relative to our position today since our own spin may have caused a particular galaxy to appear to have been spinning in a different direction at another point in space-time
tremon 2 days ago [-]
I don't understand this logic. To me, that's equivalent to saying "there's no absolute direction for which way a wheel spins, it's relative to the speed of the observer". Which makes no sense to me, because my definition of spin is measured against the axis of rotation of the object itself.
I don't see how time-intermittent frame captures from our own position affect that interpretation. Or are we using an astonomy-specific definition of spin here?
doug-moen 2 days ago [-]
It's true, there is no absolute direction for which way a wheel spins. It's relative to the observer.
If you are standing on the side of a road, and a bicycle goes by, then you may observe the wheels to rotate clockwise, while an observer on the other side of the road will observe the same wheels to rotate counter-clockwise.
The sun is said to rotate around the centre of the milky way galaxy once every 225 million years. Over that time frame, some of the galaxies we observe will flip between clockwise and counterclockwise rotation as our viewpoint changes.
But that isn't relevant here. The Space article is too vague and handwavy to make any conclusions about the research, and should be ignored. Only the original scientific paper is worth reading: https://academic.oup.com/mnras/article/538/1/76/8019798?logi...
Section 5.2 "Physics of Galaxy Rotation" seems particularly relevant.
> due to the Doppler shift effect galaxies that rotate in the opposite direction relative to the Milky Way are expected to be slightly brighter than galaxies that rotate in the same direction relative to the Milky Way. Therefore, more galaxies that rotate in the opposite direction relative to the Milky Way are expected to be observed from Earth, and the difference should peak at around the Galactic pole. That observation is conceptually aligned with the empirical data of Fig. 10, and the observation using JADES described in Section 3.
You should read the paper for the full argument.
jacksnipe 2 days ago [-]
But what if you, the observer, are also rotating? What if you’re rotating faster than the thing you’re observing?
cwillu 2 days ago [-]
I don't see how that could be so prominent as to reverse the visible arms of a spiral galaxy, what am I missing?
d1sxeyes 2 days ago [-]
It’s the same as saying you can only work out how fast something is moving in relation to something else. Your car is doing 50mph on the highway, but the earth is spinning round the sun and the sun is moving around the centre of the galaxy and the galaxy is moving compared to other galaxies and so on.
cryptonector 2 days ago [-]
> There is no absolute direction for a galaxy’s spin—it’s always relative to the observer’s perspective.
Not entirely. The galaxy is bound by gravity and the stars rotate in the galaxy around its baricenter. We can compute how fast it must be rotating from the amount of visible matter. Enter dark matter and various complications, but still, you can tell that it's rotating and which way.
And for galaxies we see edge on we can use the difference if redshift on one end versus the other to tell which way it is turning.
Y_Y 2 days ago [-]
I don't necessarily agree, in the presence of a universe (and under some reasonable cosmological assumptions) you can't just get rid of an observed rotation by a change of inertial frame. You can rotate along with it, but you'll produce a tell-tale fictitious force.
Do you or other HN commenters understand it in a satisfying way?
The author writes about the Doppler effect creating a systemic bias in brightness depending on which way the galaxies are rotating. I don't understand that argument either, but it's moot, because they state categorically that that effect would be too small to explain their results. ("This explanation is challenged by the fact that the effect of the rotational velocity have merely a mild impact on the brightness of galaxies, and therefore is not expected to lead to the dramatic difference of 50 per cent in the number of galaxies as observed through JADES.")
That's the only explanation I recognized as an explanation. Then I lost track of their argument following that. They refer to several speculative physics theories like MOND, but I don't understand them to be saying something that concretely predicts distant galaxies to appear to be rotating differently.
I'm appealing to anyone on HN who knows enough about this field to understand the meat of this argument.
perihelions 2 days ago [-]
It's a moot point, but I *really* don't understand the Doppler-shift bias mechanism either. Help?
This one of the author's other papers they cited in this one,
I'm completely lost how they're eliding between the rotation orientation of the Milky Way galaxy, and relative linear velocities with stars in other galaxies. In the special relativity argument, where does the rotation axis of the Milky Way enter?
stogot 2 days ago [-]
This is the simpler explanation. Or they need better measurements. The black hole theories are more “fun” but not logically consistent and there’s no shred of evidence beyond science fiction level ideas
sigmoid10 2 days ago [-]
This newsblog takes one piece of the paper [1] and blows it up like it's the most obvious thing ever and completely hand-waves away the alternative, while the paper itself actually provides some compelling evidence for the alternative explanation: This asymmetry is because of our own galaxy's rotation. It would be an insane coincidence to have the large scale structure of our universe be more asymmetric towards the poles of our galactic plane and the further you go away from our galaxy (especially when velocity blue shifts would obviously make one type of rotation for galaxies more visible in the high-z regime where JWST primarily looked). Forget black hole cosmology, if you believe what this article suggests, then special relativity itself may be wrong. The data is pretty sound and perfectly in line with earlier observations that found no asymmetry if you believe our own galaxy's rotation is the culprit. So if I had to bet, I'd say we misunderstood galaxies and not the universe as a whole. Mostly because galactic physics is incredibly complicated and has very whimsical empirics, whereas we have some really solid theories and data on the universe as a whole.
Thanks for link. Amazing work. I'm less than noob, so barely comprehend this topic, much less this paper.
ELI5: Per "5.2 Physics of Galaxy Rotation", could the Milky Way's relative movement, in addition to its spin, also effect the observed assymetry? In Figure 10, is the Milky Way also moving toward the blue and away from the red?
Thanks for humouring my question. Everything about astronomy and JWST just blows my mind. Like how Figure 10 sorta resembles yinyang. What a time to be alive.
jagged-chisel 2 days ago [-]
> These [baby] universes would be unobservable to us because they are also behind an event horizon, a one-way light-trapping point of no return from which light cannot escape, meaning information can never travel from the interior of a black hole to an external observer.
Also meaning that “our” blackhole (the one containing us) is unobservable from the parent universe for the same reason. So where is all this extra light/energy going in our universe? Should we not have detected an increase of energy in our universe?
alabastervlog 2 days ago [-]
I figure our whole universe so far has existed in the first nanosecond (or whatever) after the creation of the black hole in the parent universe, so very little energy or light has had time to enter.
By one or two seconds in the parent universe’s time scale, our universe will have settled down to its extremely long state of being a cold, dark void of slowly decomposing subatomic particles.
No good reason to think this, just feels right.
Aerroon 2 days ago [-]
Scales are a very interesting thing to think about. There's a theory that the universe didn't really 'start' with the big bang, that it was always there, but at a different scale. The big bang was essentially an increase in the scale of the universe, possibly in terms of time and space.
dghughes 2 days ago [-]
Our universe may be a rotating detonation engine only it's our universe being made not combustion.
lostmsu 2 days ago [-]
Time in high gravity usually flows slower than in flat regions, not faster.
jagged-chisel 2 days ago [-]
With our math, yes. But maybe that’s because we are the imaginary part of the equation.
itronitron 2 days ago [-]
what exactly is a flat region in high gravity?
jagged-chisel 2 days ago [-]
The relative time part is a really interesting thought. Thanks!
flowerthoughts 2 days ago [-]
(Complete hypothesizing from a very cursory understanding.)
Perhaps that's dark energy or vacuum energy? If mass and time truly switches places when crossing into a black hole, it would make sense that the spacetime size of this universe translates into observable mass outside it. Which might tie it to the expansion of the universe.
nextaccountic 2 days ago [-]
> If mass and time truly switches places when crossing into a black hole
What do you mean by that?
api 2 days ago [-]
It'd be neat if the universe were essentially a nested Russian doll of black holes. Our universe is a black hole with black holes inside and black holes inside them and so on, and the larger universe outside ours is also an even bigger black hole. Some of the really huge black holes in our universe might be big enough to host interesting things within, but the smaller ones probably just contain "toy" universes without much happening.
I recall reading about our universe as a black hole once -- one thing posited is that everything that is happening and what we think of as space is really information processing occurring just at the surface of the event horizon. There was some possible way of explaining non-local phenomena like entanglement that way, but I forget the details.
It's fascinating to think about how the actual universe might be something quite alien from our ordinary perception. It's not that our ordinary perception is wrong. What we're perceiving is just one perspective on something much larger and weirder. In this case our perspective would be from within this information substrate. It's almost universe-as-simulation, except that the simulation does not have a builder. It's a naturally occurring phenomenon. The Matrix has no architect, or if it does it's something fully outside the event horizon of this object and thus un-observable.
Of course at this point we're well into physicists smoking pot territory.
dingnuts 2 days ago [-]
at the bottom of the article the mundane hypothesis is presented that the measurement seen by JWST might be a calibration error caused by the rotation of the Milky Way making it appear that other galaxies have a preferred rotation.
sadly, this is likely the real explanation, but that's not very exciting
rocqua 2 days ago [-]
How does this work with matter falling into 'our' black hole and hawkins-radiation leaving our black hole?
Heck, Hawkins radiation means black holes can evaporate. Does that correspond to a universa collapsing?
Would matter falling into our black hole come shooting out of the white-hole we see?
Would time on either side of the event horizon even be related?
Aerroon 2 days ago [-]
Perhaps dark energy is hawking radiation. We just see what it's like from the inside.
Something to consider is a possible time scale difference. Eg time could be dilated for us for being around so much density.
rocqua 2 days ago [-]
It would need to be the other way around, dark energy being matter falling into our black hole. Hawking radiation should 'suck' energy out of our universe. I can't think of a satisfying source of this energy.
The best I can imagine is either space contracting (but that is gravity) or entropy increasing (but that doesn't leak energy, just free energy).
cryptonector 2 days ago [-]
> How does this work with matter falling into 'our' black hole and hawkins-radiation leaving our black hole?
We would see that at the edge (if we could see it) there's new mass and energy, but that would be obscured by what appears as the CMB for us.
> Heck, Hawkins radiation means black holes can evaporate. Does that correspond to a universa collapsing?
No, it corresponds to stuff disappearing from our universe, until someday nothing is left.
> Would matter falling into our black hole come shooting out of the white-hole we see?
We'd see it as being part of the Big Bang, behind the CMB, so we wouldn't see it.
> Would time on either side of the event horizon even be related?
Er, not in any way that we could observe, so it's not a question we could answer. But we could receive information from the outside, except that the CMB would hide it from our prying eyes.
rocqua 2 days ago [-]
Hawking radiation can't just be stuff dissapearing, because the actual singularity can dissolve. Besides, where would the stuff even leave from? I could imagine the mass flux through our event horizon being related to the energy driving space expansion (or contraction). That only makes sense if time on the inside is related to time on the outside though.
The idea that any mass that will ever fall into our black hole all simultaneously appeared at the big bang doesn't feel correct. That suggests a very specific relationship between time on the inside and outside. There are at least two moments that are distuinishable on both sides. The singularity appearing, and the singularity dissapearing. Compressing all time on the outside into the big bang means weird things for the timing of when the singularity dissapears.
d1sxeyes 2 days ago [-]
Yes but this is not a completely alien idea. We know that things that are moving through space with 100% of their movement through space (i.e., moving at the speed of light), 0% of their movement is through time.
Take a proton for example. From the proton’s perspective, its creation and destruction happen in the same instant. From our perspective, it may travel through space for some period of time between the two events.
We’re not completely sure about the nature of gravity, but given how gravity seems to interact with spacetime, it seems at least plausible that time outside the singularity compresses to a single instant from the perspective of someone inside the event horizon.
cryptonector 2 days ago [-]
> Hawking radiation can't just be stuff dissapearing
It has to be the case that black hole evaporation means that mass-energy inside the black hole "disappears" from inside the black hole. It doesn't disappear from the rest of the universe, but if we are inside a black hole then we would "see" (if we could) that Hawking radiation means stuff disappears from our inside-a-black-hole-universe.
cvoss 2 days ago [-]
> Would time on either side of the event horizon even be related?
I think that's exactly the right question to ask. And ask it for space too. Perhaps the entire history of the interior universe unfolds between the black hole's formation and its final evaporation. Perhaps a heat death of the interior universe, where everything spreads out until nothing interesting is left, can fit inside this ever shrinking volume.
rognjen 22 hours ago [-]
Wow! space.com does pretty much everything you can think of to "extract max value" from each visitor.
It's got a lot of ads, traffic arbitrage, floating unrelated videos and even back jacking...
> "The discovery by the JWST that galaxies rotate in a preferred direction would support the theory of black holes creating new universes, and I would be extremely excited if these findings are confirmed.
Its an interesting theory but to be honest, given the conditions of the event horizon, I don’t see HOW it could be proven.. That said I do feel this will turn out to be a nuance of the measurement itself but maybe that’s just my mind not comprehending the scales of what’s being measured here.
gchamonlive 2 days ago [-]
Does this mean we could look at deep space for clues about the physical rules that govern what happens beyond a black hole's event horizon?
rvogler 2 days ago [-]
i have always been wondering if the added up velocities of a series of rotating sub-systems has a relativistic effect that impacts what we observe and measure. the moon is rotating itself, around the earth, which is rotating around the sun, which is rotating ...
xqcgrek2 2 days ago [-]
This result is a big deal, and actually seems under-hyped. None of the explanations make any sense.
vitiral 2 days ago [-]
Some confusion in this thread. I think it would help folks to know that in addition to conservation of energy, our universe has conservation of angular momentum, aka mass spin.
Hope that helps!
m3kw9 2 days ago [-]
Ok but then the theory of black holes are wrong because this isn’t dense at all.
rocqua 2 days ago [-]
Black holes aren't really infinitely dense. The matter isn't concentrated at the centre, its spread out over the event horizon. As i understand the theory, they effectively suggest you could glue another universe onto the event horizon of a black hole. From the outside that is indistinguishable from 'just a black hole'.
nextaccountic 2 days ago [-]
Only the infinitesimally small singularity that is in the future of all objects inside the event horizon is supposed to be very dense. The space inside the event horizon is supposed to be normal-ish
Aerroon 2 days ago [-]
If such a singularity exists at all. The thing we "observe" about black holes is the event horizon. It could be that space inside a black hole is just regular space.
nextaccountic 2 days ago [-]
Yep! Generally speaking singularities only appear because the math is deficient in some way. Other areas of physics successfully got rid of unphysical singularities by employing better math, it's just that we don't know how to fix this aspect of general relativity (maybe quantum gravity will?)
ShinTakuya 2 days ago [-]
Black holes need not be dense. The black hole at the centre of galaxy M87 has the density of air in our atmosphere. The larger the black hole, the less dense it is. So that alone doesn't preclude us existing inside of one.
m3kw9 2 days ago [-]
That’s news to me, I was taught that the mass collapses into it self it creates more gravity and more matter gets sucked in because the mass is so dense. So at which point does it become less dense?
ShinTakuya 2 days ago [-]
Keep in mind that my own knowledge of physics is very rusty, so some of this is definitely making bad assumptions.
The density in the singularity (centre) of the black hole is in theory infinite. But the event horizon (the part where light no longer escapes) is not the singularity, it's simply where the gravity becomes so strong that light can't escape.
Think of it as the sun vs the planets - we're not in the sun, but we still feel its effects. The density of the solar system isn't the same as the density of the sun. This is bad analogy because the same mathematics/physics doesn't apply, but it should help you get the general picture based on your original assumption.
In general, the heavier the black hole, the less dense it is when measured from the event horizon. So in theory, it's possible to have a black hole so heavy that the event horizon contains the entire universe. In fact, the known universe is heavy enough to be a black hole 3 times the known radius of the universe. But as we know from stars that turn into black holes, just because something is heavy enough to be a black hole, doesn't mean it is one yet.
d1sxeyes 2 days ago [-]
As long as it’s dense enough that light can’t escape, it’s a black hole. You can achieve that with extreme density or huge volumes of mass. The more massive an object, the less dense it needs to be to be a black hole.
jpalawaga 2 days ago [-]
An entire universe crammed inside the event horizon seems pretty dense to me! Makes you wonder how much matter would be in the parent universe.
Sharlin 2 days ago [-]
Something something Betteridge's law of headlines.
Rendered at 17:56:06 GMT+0000 (Coordinated Universal Time) with Vercel.
> Another explanation for why the JWST may have seen an overrepresentation of galaxies rotating in one direction is that the Milky Way's own rotation could have caused it.
> Previously, scientists had considered the speed of our galaxy's rotation to be too slow to have a non-negligible impact on observations made by the JWST.
> “If that is indeed the case, we will need to re-calibrate our distance measurements for the deep universe," Shamir concluded. "The re-calibration of distance measurements can also explain several other unsolved questions in cosmology such as the differences in the expansion rates of the universe and the large galaxies that according to the existing distance measurements are expected to be older than the universe itself."
How can local movement of stars within the Milky Way affect which way spiral galaxy arms are pointing?
[0] https://academic.oup.com/mnras/article/538/1/76/8019798.
(Tricky part is deciding it's another body from a picture. You would need a second JWST preferably far in the other Lagrange point. Stereoscopy solves it directly. You can )
The thing is, you need another galaxy in the way to be sure, or a black hole. Theoretically our Sun can serve. [] Or the supermassive black hole in the center of our galaxy, but the sensitivity might be a bit compromised.
And long observation time.
[] https://en.m.wikipedia.org/wiki/Solar_gravitational_lens It's a bit hard to put satellites in the right place.
So I’d suspect they’re saying time and distance would need to be factored in rather than just looking at static images relative to our position today since our own spin may have caused a particular galaxy to appear to have been spinning in a different direction at another point in space-time
I don't see how time-intermittent frame captures from our own position affect that interpretation. Or are we using an astonomy-specific definition of spin here?
If you are standing on the side of a road, and a bicycle goes by, then you may observe the wheels to rotate clockwise, while an observer on the other side of the road will observe the same wheels to rotate counter-clockwise.
The sun is said to rotate around the centre of the milky way galaxy once every 225 million years. Over that time frame, some of the galaxies we observe will flip between clockwise and counterclockwise rotation as our viewpoint changes.
But that isn't relevant here. The Space article is too vague and handwavy to make any conclusions about the research, and should be ignored. Only the original scientific paper is worth reading: https://academic.oup.com/mnras/article/538/1/76/8019798?logi...
Section 5.2 "Physics of Galaxy Rotation" seems particularly relevant.
> due to the Doppler shift effect galaxies that rotate in the opposite direction relative to the Milky Way are expected to be slightly brighter than galaxies that rotate in the same direction relative to the Milky Way. Therefore, more galaxies that rotate in the opposite direction relative to the Milky Way are expected to be observed from Earth, and the difference should peak at around the Galactic pole. That observation is conceptually aligned with the empirical data of Fig. 10, and the observation using JADES described in Section 3.
You should read the paper for the full argument.
Not entirely. The galaxy is bound by gravity and the stars rotate in the galaxy around its baricenter. We can compute how fast it must be rotating from the amount of visible matter. Enter dark matter and various complications, but still, you can tell that it's rotating and which way.
And for galaxies we see edge on we can use the difference if redshift on one end versus the other to tell which way it is turning.
See e.g. https://en.wikipedia.org/wiki/Mach's_principle
The author writes about the Doppler effect creating a systemic bias in brightness depending on which way the galaxies are rotating. I don't understand that argument either, but it's moot, because they state categorically that that effect would be too small to explain their results. ("This explanation is challenged by the fact that the effect of the rotational velocity have merely a mild impact on the brightness of galaxies, and therefore is not expected to lead to the dramatic difference of 50 per cent in the number of galaxies as observed through JADES.")
That's the only explanation I recognized as an explanation. Then I lost track of their argument following that. They refer to several speculative physics theories like MOND, but I don't understand them to be saying something that concretely predicts distant galaxies to appear to be rotating differently.
I'm appealing to anyone on HN who knows enough about this field to understand the meat of this argument.
This one of the author's other papers they cited in this one,
https://www.mdpi.com/2073-8994/15/6/1190
I'm completely lost how they're eliding between the rotation orientation of the Milky Way galaxy, and relative linear velocities with stars in other galaxies. In the special relativity argument, where does the rotation axis of the Milky Way enter?
[1] https://academic.oup.com/mnras/article/538/1/76/8019798
ELI5: Per "5.2 Physics of Galaxy Rotation", could the Milky Way's relative movement, in addition to its spin, also effect the observed assymetry? In Figure 10, is the Milky Way also moving toward the blue and away from the red?
Thanks for humouring my question. Everything about astronomy and JWST just blows my mind. Like how Figure 10 sorta resembles yinyang. What a time to be alive.
Also meaning that “our” blackhole (the one containing us) is unobservable from the parent universe for the same reason. So where is all this extra light/energy going in our universe? Should we not have detected an increase of energy in our universe?
By one or two seconds in the parent universe’s time scale, our universe will have settled down to its extremely long state of being a cold, dark void of slowly decomposing subatomic particles.
No good reason to think this, just feels right.
Perhaps that's dark energy or vacuum energy? If mass and time truly switches places when crossing into a black hole, it would make sense that the spacetime size of this universe translates into observable mass outside it. Which might tie it to the expansion of the universe.
What do you mean by that?
I recall reading about our universe as a black hole once -- one thing posited is that everything that is happening and what we think of as space is really information processing occurring just at the surface of the event horizon. There was some possible way of explaining non-local phenomena like entanglement that way, but I forget the details.
It's fascinating to think about how the actual universe might be something quite alien from our ordinary perception. It's not that our ordinary perception is wrong. What we're perceiving is just one perspective on something much larger and weirder. In this case our perspective would be from within this information substrate. It's almost universe-as-simulation, except that the simulation does not have a builder. It's a naturally occurring phenomenon. The Matrix has no architect, or if it does it's something fully outside the event horizon of this object and thus un-observable.
Of course at this point we're well into physicists smoking pot territory.
sadly, this is likely the real explanation, but that's not very exciting
Would matter falling into our black hole come shooting out of the white-hole we see?
Would time on either side of the event horizon even be related?
Something to consider is a possible time scale difference. Eg time could be dilated for us for being around so much density.
We would see that at the edge (if we could see it) there's new mass and energy, but that would be obscured by what appears as the CMB for us.
> Heck, Hawkins radiation means black holes can evaporate. Does that correspond to a universa collapsing?
No, it corresponds to stuff disappearing from our universe, until someday nothing is left.
> Would matter falling into our black hole come shooting out of the white-hole we see?
We'd see it as being part of the Big Bang, behind the CMB, so we wouldn't see it.
> Would time on either side of the event horizon even be related?
Er, not in any way that we could observe, so it's not a question we could answer. But we could receive information from the outside, except that the CMB would hide it from our prying eyes.
The idea that any mass that will ever fall into our black hole all simultaneously appeared at the big bang doesn't feel correct. That suggests a very specific relationship between time on the inside and outside. There are at least two moments that are distuinishable on both sides. The singularity appearing, and the singularity dissapearing. Compressing all time on the outside into the big bang means weird things for the timing of when the singularity dissapears.
Take a proton for example. From the proton’s perspective, its creation and destruction happen in the same instant. From our perspective, it may travel through space for some period of time between the two events.
We’re not completely sure about the nature of gravity, but given how gravity seems to interact with spacetime, it seems at least plausible that time outside the singularity compresses to a single instant from the perspective of someone inside the event horizon.
It has to be the case that black hole evaporation means that mass-energy inside the black hole "disappears" from inside the black hole. It doesn't disappear from the rest of the universe, but if we are inside a black hole then we would "see" (if we could) that Hawking radiation means stuff disappears from our inside-a-black-hole-universe.
I think that's exactly the right question to ask. And ask it for space too. Perhaps the entire history of the interior universe unfolds between the black hole's formation and its final evaporation. Perhaps a heat death of the interior universe, where everything spreads out until nothing interesting is left, can fit inside this ever shrinking volume.
It's got a lot of ads, traffic arbitrage, floating unrelated videos and even back jacking...
To cross her course
Are swallowed by
A fearsome force
Through the void
To be destroyed
Or is there something more?
Atomized — at the core
Or through the Astral Door —
To soar…"
https://www.rush.com/songs/cygnus-x-1-book-one-the-voyage/
Its an interesting theory but to be honest, given the conditions of the event horizon, I don’t see HOW it could be proven.. That said I do feel this will turn out to be a nuance of the measurement itself but maybe that’s just my mind not comprehending the scales of what’s being measured here.
Hope that helps!
The density in the singularity (centre) of the black hole is in theory infinite. But the event horizon (the part where light no longer escapes) is not the singularity, it's simply where the gravity becomes so strong that light can't escape.
Think of it as the sun vs the planets - we're not in the sun, but we still feel its effects. The density of the solar system isn't the same as the density of the sun. This is bad analogy because the same mathematics/physics doesn't apply, but it should help you get the general picture based on your original assumption.
In general, the heavier the black hole, the less dense it is when measured from the event horizon. So in theory, it's possible to have a black hole so heavy that the event horizon contains the entire universe. In fact, the known universe is heavy enough to be a black hole 3 times the known radius of the universe. But as we know from stars that turn into black holes, just because something is heavy enough to be a black hole, doesn't mean it is one yet.