This notion that Stranger posted earlier has been niggling at my brain.
As a way of visualization, picture a universe next to ours (in multiverse theory) and a gravity well was created in it so strong it tore out the ‘bottom’ (white hole?) and splashed into ours. That entry point would be the singularity and the speeding up of the expansion is the result of matter continuing flush into our universe from the other.
And don’t bother asking me for details, I’ve done the math - it checks out.,
The reason I asked is my (flawed, I’m sure) understanding that Einstein considered space and time to be so related that he referred to them as space-time. Which seems to me to say that if there is no end of space in the universe, then there is no end of time. That is, if we are in continuous expansion of the universe, then it is unending. OTOH, if there is such a thing as heat death of the universe (where time would end), then there is obviously a space limit as well.
From what I understand, in addition to the Big Bang itself, we’re talking about black holes. When you say that they might not all be the same thing, I assume you mean that the supermassive black holes at the center of galaxies, like our own Sagittarius A* might be something different than the black holes that form when a really big star goes supernova, and that both of those things might also be different from what are called primordial black holes. Or maybe they are all the same, just different sizes. Either way, I assume that what you mean by saying the the term “singularity” does not actually apply to those physical entities is that none of those things are actually infinitely small and therefore not infinitely dense, because the denominator in the mass / volume = density formula doesn’t actually equal zero. Does that sound correct?
Well we occasionally refer to the start of time as involving a singularity. Black holes currently throw up singularities in understanding them. Whether the black hole is rotating or not makes a big difference. So the history of a black hole may matter. But other than that they are all the same.
But nobody actually believes that there is a magical thing called a singularity actually there. Just a region where we don’t understand what is going on.
Some singularities are just an artefact of how we do the mathematics and can be eliminated easily. Black holes currently can’t be tamed so easily.
But I really don’t believe that many physicists think that matter is actually squeezed out of existence in an infinity dense point. That raises more questions than it answers. Given we know our theories are incomplete in just these areas it seems very presumptuous to be making statements about the nature of universe based on them.
Infinity gets thrown around as if it is just another number. And its partner, the singularity, just as much. There really isn’t much actual science here. Boundaries to science yes, but science you can write checks on, no.
Even the nature of space-time gets shaky at these limits. Hence questions about the nature of time wrt space. The mathematics of 4D space time are very solid. But the question of whether time exists into the past or future gets messy. Mostly it is ignored. But if you want to talk about infinite space and time it might be worthy of question.
There are certainly those of the opinion that space-time as we find it is an emergent property of something deeper. Given existing problems with locality and maybe causality, this is likely true.
Imagine a circle sitting atop a line…a tangent.
tangent.png (650×450)
The line has a slope of zero.
As you rotate the line to a 45 degree angle, the slope is 1.
desktop_5197b052-c5ad-4a0f-86a5-2359b826cfbf.png (472×280)
Rotate the tangent line vertically,
Circle3.gif (196×205)
The slope is infinite.
So infinities can be generated from finite initial conditions.
That is an interesting and thought provoking example… But slope is just a concept - it’s a way of looking at something - it’s not an entity that has existence in its own right, right?
Well it isn’t far off asking where two parallel lines intersect.
Just depends on your geometry basis. Lots of Euclidean bias here as well.
Lots of simple numerical infinities can be removed by suitable changes in your coordinates. If your tangent has an annoying slope, move where you stand. If it is still being annoying ask what you are using it for. You will probably find that not calculating the slope but expanding the calculation of what you really want, you can reduce the arithmetic so that you don’t actually need to calculate a slope and never get a singularity.
This sort of thing is numerical methods 101.
Sometimes things work much better with a different coordinate system. The favourite next in line is polar coordinates. A huge amount of grief vanishes for some problems just doing that. Again basic toolset stuff for engineers and physicists. Various dual spaces come next in line. And for signals engineers, a quick Fourier transform and work in frequency space will get you far. And it keeps on going. I still remember when I learnt how weather models can usefully run in spherical harmonics aka spectral models. Not perfect, but fix a lot of annoying issues. Including annoying problems at the poles.
The problem we have with black holes is that there isn’t any such magic. They resolutely refuse to budge. But this doesn’t give us license to start making shit up. Sadly there is a lot of made up crap, a lot from people who know better, but having once tasted the limelight crave it more. That and making money writing books.
There are Penrose–Hawking (et al.) type theorems that give some general conditions that force a space-time to have an “edge”, as it were. It is geometric, not merely a coordinate trick.
Can you expand on this a bit? Does this depend on frame of reference? I’m confused.
Although that is deemed correct by scientists (and Chronos, so it must be true) I cannot see how it is possible to distinguish this hypothesis from the hypothesis that the Universe is constant in size and everything in it including us and our measuring instruments is shrinking at a steady rate. How could you tell?
It seems the trouble is not as bad as click-bait would suggest, and those “little red dot galaxies” are not fully formed after all:
Doesn’t this have to do with color shifts that indicate that things are moving away from us in all directions? Would shrinking produce the same color shifts? Or is the “color shifts = movement of objects” theory incorrect?
In the latter case we’d see no expansion of the universe in the first place, since spacetime is a “thing” and would shrink as well. That hypothetical contains the assumption that spacetime is full of “stuff” that is either moving apart or shrinking to create the illusion of that; but spacetime is just as much “stuff” as everything else. And if everything else but spacetime was shrinking it would do probably lethal things to how the laws of physics for matter work.
Prove it!
I think the disconnect here is that sometimes we use the term “universe” to mean “everything that exists,” and other times to mean “everything we can observe”. When they say “the universe was once a single dense point” they’re talking about the latter.
It’s entirely possible that our observable universe was once a single dense point, in an infinitely dense, unending continuum. As that continuum stretched out due to inflation and expansion, like a big rubber sheet being stretched forever, that “one point” became everything we can observe today.
But that doesn’t mean the rest of the unobservable universe stopped existing (though to all intents and purposes it stopped existing for us, because we can never see it or interact with it in any way).
Depends. Are you talking about this universe, or the multiverse?
I hope this isn’t too tangential of a question, but I think it’s related. In 150 billion years, the CMBR will be undetectable, and all other galaxies outside of our own will be invisible due to the expansion of the universe. If a new civilization, similar to ours, were to form in another solar system, would they ever know that other galaxies ever existed? What would their observable universe be? And would their reality be different than ours, in that they truly would occupy a “special” place in the universe, as it would not be homogeneous for them (as it is for us)?
It makes no difference. If it begins as finite, it can’t become infinite by merely getting bigger
Say the universe doubles in size in the first second, doubles again in the next half-second, again in the next quarter-second, and so on. Then I wait 2.1 seconds.
It seems like that would be a simple problem that could be solved using integral calculus. But in the real world one runs into the problem of the Planck time. Once one gets to 5.4x10^-44 seconds, it makes no real world sense to halve that and ask about a doubling at 2.7x10^-44 seconds, and further halving down to 1.35X10^-44 and so on also make no sense. So at that point it would become a simple algebraic equation where the doubling happens every 5.4x10^-44 seconds. Which is of course a really really big number. But not infinite. At least that’s my understanding of what the Planck time means, that is that considering smaller amounts of time makes no sense in the real world.
Planck time isn’t really about some underlying granularity to time (well, it might be, but that isn’t necessarily the case). It’s more that the laws of physics break down at that scale. That doesn’t mean the universe can’t “do stuff” on a shorter timescale than that, just that our models start to go wonky.
In any case, I wasn’t being 100% serious there, but what I described is sometimes called a “supertask.” We don’t have evidence that supertasks can actually happen in the real world… but we don’t have evidence that they can’t, either (except for special cases).
