Is the universe a black hole? No

[p1t1o]

So you guys know this idea - a black hole with a mass of the universe would have an event horizon roughly the same size as the universe. Or that technically the edge of the observable universe is an event horizon because light cannot escape. Or something. And that this causes some people to think that the universe itself is a black hole that we live inside.

Now I remember someone quite convincingly show that this is not true, but I cant remember why nor can I track down the thread.

Can anyone sum up the refutation briefly?

Thanks!

[Soupspoon]

Not a refutation, but given that beyond the EH 'inward' is a dimension that cannot be fought against (in either direction, it really doesn't matter which) I've always thought it wise to treat the radial dimension as we outside deal with time. The other two space dimensions can wrap over to the other two spherical coordinates. If this has applied to our universe then the universe beyond has a spacial dimension in the place of that which we see as time.

OTOH, time goes screwy when crossing the EH. Factored by √(1-(v²/c²)) (as with the inexorable space dimension) that which we currently know of as it in d² = x² + y² + z² + (it)² is maybe transformed to a non-imaginary dimension via iit. Maybe we are the other side of an event-horizon, to an equivalent (but still transformed) universe.

Or via the singularity. One 'logical' idea is that the upper-limit of our universe folds out into an infalling event horizon, as much as it is possible that the infalling 'through' the singularity is the feedstock to the Big Bang singularity of an adjacent cosmos.

Now discuss whether the quantity of 'feedstock' of a black hole within one cosmos is in direct correlation to the mass of the universe beyond, before realising that this might be moot for other reasons.

For one, black holes evaporate (if Hawking wasn't too far wrong), so maybe that's the refutation? Our universe is clearly not evaporating. Though that does happen by the hole swallowing one of a pair of virtual particles (sort of), so that the other carries mass away. Does the captured one provide the mass? Or if we might have doubts about the temporal polarity across the join of existence, could the particles and the end-of-life 'popping' of the dying singularity be related to the expansionist acceleration of the early (flipside) cosmos? (Mind you, it's also possible to 'explain' a steady-state universe away, if that were the favoured theory, by similar twists giving us the 'infill' matter for our reality, so I wouldn't so easily trust such simplistic phiosophical 'enlightenments' as these.)



I doubt this actually helps answer the question, but and of course there are many pitfalls in the logic, but it'll get you past the standard armchair philosophy in ways slightly better than taking on the Timecube theory!

[doogly]

Here we go

https://www.preposterousuniverse.com/bl ... lack-hole/

[ijuin]

As to the universe evaporating via Hawking radiation, a black hole with the mass of the observable universe would take on the order of 10^120 years to evaporate, meaning that within the lifespan of the Earth it would have lost less than ONE solar mass.

[Soupspoon]

Lifespan at our side. Greater minds than ours know quite what factors (and signs) the experience of time and quantity seen on the other side. Especially across a possibly necessarily asymmetric joining of realities.

(As to there being nothing outside the universe to be expanding into as a disequivalence to the black hole, as per the article, it sort of ignores the topology of the black hole having nothing beyond at least one of its limits, in a manner that may injectively relate. Not to say that everything does so map, but it probably needs to be refuted comprehensively before it can be called a fait accompli.)

[p1t1o]

Is there any school of thought that says "Look, we currently have very-little-to-no idea what it is like inside a black hole, in physical reality, so the question is unverifiable either way and therefore meaningless." ?

[doogly]

Is there any school of thought that says "Look, we currently have very-little-to-no idea what it is like inside a black hole, in physical reality, so the question is unverifiable either way and therefore meaningless." ?

No, we can definitely say that it is a bad question. The answer isn't NULL, it's NO.

[Tub]

Is there any school of thought that says "Look, we currently have very-little-to-no idea what it is like inside a black hole, in physical reality, so the question is unverifiable either way and therefore meaningless." ?

We have zero experimental evidence about the inside of a black hole, but we do have experimental evidence that the laws of physics aren't overturned by crossing an event horizon (remember, you're crossing somebody's event horizon right now), and we have experimental evidence for those laws of physics to remain valid in a broad range of circumstances.

The center of a black hole is certainly outside the range of physics we can accurately describe (still lacking a tested theory of quantum gravity), but we can make many predictions about the outer parts that we're confident about - like the curvature. The inside of a black hole is certainly not spatially flat; the universe we live in is.

[doogly]

(remember, you're crossing somebody's event horizon right now)

If you are at this moment doing some very deep boning or surgery, maybe.

[SuicideJunkie]

A time-reversed, higher dimensional equivalent of a black hole? Space is expanding because our 3d shell is collapsing towards the big bang but we're experiencing it backwards?
Could be a story plot. Once matter is diluted to a critical point, time becomes spacelike but with a lot of momentum by default, and hijinks ensue with half the cast moving through ex-time at arbitrary speeds while always able to get to their meetings on time despite not being able to get there at the right age.

[Carmeister]

randall mentioned this hypothesis in a what-if https://what-if.xkcd.com/140/ (look in the note [6]) the short answer is that it's not true, http://www.preposterousuniverse.com/blo ... lack-hole/, I see that someone linked this article earlier in the thread too.

[Soupspoon]

(As to there being nothing outside the universe to be expanding into as a disequivalence to the black hole, as per the article, it sort of ignores the topology of the black hole having nothing beyond at least one of its limits, in a manner that may injectively relate. Not to say that everything does so map, but it probably needs to be refuted comprehensively before it can be called a fait accompli.)

Not saying it's not false, but that refutation still doesn't go far enough to show why various (obviously non-obvious) versions are false, as well as the simple one it covers.

[IvanD]

I would say that on the contrary, the universe is space-time, just the black hole is surely the absence of space-time, or rather, the black hole will be just the inverse of the universe. Nice symmetrical environment....

[Xanthir]

A black hole is not the "absence of space-time".

[Soupspoon]

Time-space?

[Xanthir]

Yes, that's correct. A black hole is time-space.

[ucim]

Yes, that's correct. A black hole is time-space.

But if Apple made a black hole, it would be negative space-time. Which brings us back to do.

Jose

[p1t1o]

Yes, that's correct. A black hole is time-space.

But if Apple made a black hole, it would be negative space-time. Which brings us back to do.

Jose

If Apple made a black hole, it would only attract very specific types of particle, and probably not the same types as most other black holes.
It would also be white.

[Pfhorrest]

Apple's version isn't called a black hole, it's called a Reality Distortion Field™, and it is mediated by bogons rather than gravitons. Steve Jobs was the only known example of one.

[ucim]

Apple's version isn't called a black hole, it's called a Reality Distortion Field™, and it is mediated by bogons rather than gravitons. Steve Jobs was the only known example of one.

You're obviously not following the news from Washington.

Jose

[Quizatzhaderac]

Our universe is clearly not evaporating.

<BS>That's happens to photons when they red-shift to be longer than the Hubble length</BS>

Is there any school of thought that says "Look, we currently have very-little-to-no idea what it is like inside a black hole, in physical reality, so the question is unverifiable either way and therefore meaningless." ?

Although, I'd say the question of "Given that the universe isn't technically a black hole, is it still a black hole like thing?" would be regarded as meaningless nonsense. Which is basically what lay people are asking when they keep talking about black hole universes once they learn the Schwarzschild solution doesn't apply.

[Eebster the Great]

To be fair, the Schwarzschild metric doesn't apply to real black holes either, but it applies pretty well to most normal stars.