Philosophy Now Forum

Noax wrote: ↑Mon Nov 18, 2024 1:19 am The cosmological constant needs to be something, meaning expansion is necessary for there to be a universe. If it isn't currently expanding, it was in the past, and we happen to be observing at its moment of largest size before it begins to contract to a big crunch. So we're at a privileged moment in time.
We're also at a privileged location in space since we're posited to be reasonably opposite this black hole.
All these preferred locations make it sound like the universe was created just for us. Just saying.

There's no such thing as an antimatter black hole. They have but three properties: mass, angular momentum, and charge. A hole created by mostly matter is therefore no different than one created by mostly antimatter. So why posit it since the argument doesn't seem to depend on it.

You're positing a large mass at the far end of the universe. Why does it need to be a black hole at all? Any large mass, however spread out, will produce an identical gravitational effect as a concentrated one, at least at a radius beyond the limits of the mass. In other words, if our sun was today compressed into a black hole, the planets would continue their current orbits with no change at all.

If it was at a black hole, the mass of the other material would increase its radius to include it. So no, the universe cannot have all the mass at one location spreading out into the empty part of the hypersphere. The big bang can not happen at a location in space, and you are seemingly trying to describe that.

The big distant mass would exert a greater pull in the past when it was closer. It cannot suddenly acquire more mass from nowhere. Also, the mass is beyond the visible universe, which means anything outside that radius cannot have an effect on us or anything we see. That's what visible universe means.

Yes, that's a problem. We see expansion happening slower the further we look, but in your model, further implies being closer to this imbalanced mass pulling it all away.

Only in flat spacetime, which this isn't. It is even worse than quadratic since it has zero effect near our privileged location since it pulls in all directions more or less equally.

Keep in mind that the Hubble constant is not a constant. It can be crudely expressed as 1/T where T is the age of the universe, and that means that it is a function of time, being far larger in the past.

Noax wrote: ↑Mon Nov 18, 2024 1:19 am I'm not often logged in here, but I notice no actual reply to this OP. Hope a month late is not too much.

Atla wrote: ↑Sat Oct 19, 2024 7:36 am What if the observable universe isn't expanding, but instead the total universe is a hyperspehrical space with a say roughly half-universe sized anti-matter black hole at the exact opposite point within the hypersphere from our perspective, roughly at an equal distance from us in every direction beyond the edge of the observable universe?

The cosmological constant needs to be something, meaning expansion is necessary for there to be a universe. If it isn't currently expanding, it was in the past, and we happen to be observing at its moment of largest size before it begins to contract to a big crunch. So we're at a privileged moment in time.
We're also at a privileged location in space since we're posited to be reasonably opposite this black hole.
All these preferred locations make it sound like the universe was created just for us. Just saying.

There's no such thing as an antimatter black hole. They have but three properties: mass, angular momentum, and charge. A hole created by mostly matter is therefore no different than one created by mostly antimatter. So why posit it since the argument doesn't seem to depend on it.

You're positing a large mass at the far end of the universe. Why does it need to be a black hole at all? Any large mass, however spread out, will produce an identical gravitational effect as a concentrated one, at least at a radius beyond the limits of the mass. In other words, if our sun was today compressed into a black hole, the planets would continue their current orbits with no change at all.

And after the "Big Bang", everything was flung out in every direction from that black hole

If it was at a black hole, the mass of the other material would increase its radius to include it. So no, the universe cannot have all the mass at one location spreading out into the empty part of the hypersphere. The big bang can not happen at a location in space, and you are seemingly trying to describe that.

and then about 5 billion years ago the gravity of the black hole overcame the inertia of the inital explosion and everything started falling back towards the black hole

The big distant mass would exert a greater pull in the past when it was closer. It cannot suddenly acquire more mass from nowhere. Also, the mass is beyond the visible universe, which means anything outside that radius cannot have an effect on us or anything we see. That's what visible universe means.

But then I guess the first problem that comes up is that the Hubble constant shouldn't be a linear constant but a quadratic constant

Yes, that's a problem. We see expansion happening slower the further we look, but in your model, further implies being closer to this imbalanced mass pulling it all away.

because the strength of gravity changes quadratically over distance.

Only in flat spacetime, which this isn't. It is even worse than quadratic since it has zero effect near our privileged location since it pulls in all directions more or less equally.

Keep in mind that the Hubble constant is not a constant. It can be crudely expressed as 1/T where T is the age of the universe, and that means that it is a function of time, being far larger in the past.

Atla wrote: ↑Mon Nov 18, 2024 6:06 am

Noax wrote: ↑Mon Nov 18, 2024 1:19 am The cosmological constant needs to be something, meaning expansion is necessary for there to be a universe. If it isn't currently expanding, it was in the past, and we happen to be observing at its moment of largest size before it begins to contract to a big crunch. So we're at a privileged moment in time.
We're also at a privileged location in space since we're posited to be reasonably opposite this black hole.
All these preferred locations make it sound like the universe was created just for us. Just saying.

Nah, it would just be the Anthropic principle at play. A self-aware civilization necessarily finds itself in a world capable of having a self-aware civilization. We may yet find that the whole observable universe is another Goldilocks zone.

There's no such thing as an antimatter black hole. They have but three properties: mass, angular momentum, and charge. A hole created by mostly matter is therefore no different than one created by mostly antimatter. So why posit it since the argument doesn't seem to depend on it.

You're positing a large mass at the far end of the universe. Why does it need to be a black hole at all? Any large mass, however spread out, will produce an identical gravitational effect as a concentrated one, at least at a radius beyond the limits of the mass. In other words, if our sun was today compressed into a black hole, the planets would continue their current orbits with no change at all.

It doesn't have to be a black hole, but it probably should be half-universe worth of anti-matter. It's for a bigger reason, I'm into speculations about the universe which make sense to me.

Atla wrote: ↑Mon Nov 18, 2024 6:06 am Only absolute simmetry makes sense to me, which also means that perhaps the simplest explanation for the missing antimatter could be that it's beyond the observable universe. (If it was here, we would blow up, so it can't be here, we may be in a Goldilocks zone.)

Atla wrote: ↑Mon Nov 18, 2024 6:06 am But it doesn't have to be a black hole. Maybe the other half of the universe looks just like our half of the universe, with galaxies and such. Maybe there is absolutely simmetry and there are even our exact copies made of anti-matter.

If it was at a black hole, the mass of the other material would increase its radius to include it. So no, the universe cannot have all the mass at one location spreading out into the empty part of the hypersphere. The big bang can not happen at a location in space, and you are seemingly trying to describe that.

Atla wrote: ↑Mon Nov 18, 2024 6:06 am

The big distant mass would exert a greater pull in the past when it was closer. It cannot suddenly acquire more mass from nowhere. Also, the mass is beyond the visible universe, which means anything outside that radius cannot have an effect on us or anything we see. That's what visible universe means.

Yes, that's a problem. We see expansion happening slower the further we look, but in your model, further implies being closer to this imbalanced mass pulling it all away.

Yes but the inertia from the Big Bang could have dominated in the first 10 billion years despite the initial greater gravitational pull.
Now the mass being beyond the visible universe and therefore not having gravity is indeed a problem. Maybe it wasn't beyond it at the time of the Big Bang, and our region of space acquired a gravitational "tilt"? Maybe dark energy isn't limited by space?

Again I'm just speculating nonsense, for fun.

Atla wrote: ↑Mon Nov 18, 2024 6:06 am

Only in flat spacetime, which this isn't. It is even worse than quadratic since it has zero effect near our privileged location since it pulls in all directions more or less equally.

Keep in mind that the Hubble constant is not a constant. It can be crudely expressed as 1/T where T is the age of the universe, and that means that it is a function of time, being far larger in the past.

I'm talking about hyperspherical flat spacetime. I find the idea that space necessarily has to curve in order to be hyperspherical, to be just a confusion.

Atla wrote: ↑Mon Nov 18, 2024 6:06 am But it doesn't have to be a black hole. Maybe the other half of the universe looks just like our half of the universe, with galaxies and such. Maybe there is absolutely simmetry and there are even our exact copies made of anti-matter.

When a half-universe sized black hole collides with a half-universe sized anti-matter black hole as the Big Bang

Yes but the inertia from the Big Bang could have dominated in the first 10 billion years despite the initial greater gravitational pull.

Now the mass being beyond the visible universe and therefore not having gravity is indeed a problem.

Maybe it wasn't beyond it at the time of the Big Bang

Again I'm just speculating nonsense, for fun

I'm talking about hyperspherical flat spacetime.

Noax wrote: ↑Mon Nov 18, 2024 11:33 pm This part is more reasonable, but you require some sort of asymmetry to attempt to justify the galaxies far away from us being sucked for some reason towards the other half despite the other half being outside the past light cone of any of them. Past light cone defines what stuff is considered part of our visible universe. It doesn't mean we can see that far. The furthest light we see today has ever been is at a proper distance from us of about 6 GLY, not 48.

That inertia is all there is, and the view from anywhere would be of expansion slowing. Yes, it did slow at first, but gravity of some mass that is 1) getting further away, and 2) not growing and 3) outside the causal cone, cannot suddenly do something it wasn't doing before, and doing harder before.

It does have gravity since there's mass, but no change from outside the visible universe can have any effect inside.

Nothing can leave a visible universe, by definition. New stuff comes in over time, but nothing leaves. This is as opposed to the event horizon where objects cross outward over time and by definition, nothing can cross in. The event horizon is currently about 16 GLY away, about a third the way to the edge of the visible universe, and only a little beyond the current Hubble radius where comoving objects are receding at c relative to the cosmic frame.

Again, no such thing as an antimatter (or matter) black hole. Two similar mass black holes colliding reacts the same whether each was formed by matter collapse, or one by antimatter collapse. There's no matter or antimatter left of either, only mass parameter.

Well that's what it comes down to. If you have fun doing it, fine, just don't expect it to hold up to analysis. Maybe my analysis is just throwing water on your vision. Should I shut up?

A hypersphere is positively curved spacetime where parallel straight lines don't stay parallel and eventually meet. And the quadratic rule of gravity is a law of Newton's and falls apart with really large and/or dense masses, and of course the lack of flat spacetime that Newton's theories rely on.

Atla wrote: ↑Tue Nov 19, 2024 2:06 am You seem to be using definitions based on a forever expanding universe

Maybe, I don't really understand this part. Sure, we can't tell what would happen inside the event horizon of a matter-antimatter black hole collision, because we can't see inside the event horizon. But how do you know for sure that it would behave the same in there, as say a matter-matter blackhole collision?

Well that's what it comes down to. If you have fun doing it, fine, just don't expect it to hold up to analysis. Maybe my analysis is just throwing water on your vision. Should I shut up?

By hyperspherical I meant that if you could travel in one direction in spacetime "in a straight line", you would eventually end up where you started.

The universe doesn't have to be curved to be finite and unbounded.

Noax wrote: ↑Tue Nov 19, 2024 3:37 am Good point. The model you describe would have no event horizon at all, but you're also doing it when you reference the size of the visible universe, a figure that comes from the ΛCDM model. The size of your visible universe has not been computed, but the part about nothing being able to leave it still applies. It cannot contract. one just gets affected by ever more distant events. If the universe contracts enough, the visible universe becomes larger than the size of the universe and you can see the same object in more than one direction.

No-hair theorem says that there are only the three properties I listed. It's a theorem, meaning there's no debate about it. The contents of a black hole cannot effect the outside. In coordinate terms, all interior events are in the future of any outside events, and events in the future cannot affect past events, which would be backwards causality.

Yes, assuming the expansion is not accelerating. Even with infinite but not accelerating expansion, yes, you'd eventually come back to where you started. If there's acceleration, then there is an event horizon, and you can't go further than that.

If it's a hypersphere, then yes it does have to be curved. A torrid universe (like in asteroids video game) is finite, unbounded, and flat, but it's not spherical. So given that example, I agree with your statement.

Atla wrote: ↑Tue Nov 19, 2024 5:05 am Actually I don't think the total universe ever literally expands or contracts here.

But I'm talking about a finite but boundless universe in spacetime, so the past and future have to meet at a distant point in our past/future.

A better explanation for dark energy might be that it's just antigravity.

You seem to be talking about going around in space, I was talking about going around in spacetime.

I said "hyperspherical", to differentiate it from a literal hypersphere. I'm actually talking about a hyperspherical flat universe (and not just in space but also in time), but it's impossible to visualize it.

Things like spheres and toruses are just geometrical concepts that may have nothing to do with the "shape" of the universe.

Atla wrote: ↑Tue Nov 19, 2024 5:05 am

Noax wrote: ↑Tue Nov 19, 2024 3:37 am Good point. The model you describe would have no event horizon at all, but you're also doing it when you reference the size of the visible universe, a figure that comes from the ΛCDM model. The size of your visible universe has not been computed, but the part about nothing being able to leave it still applies. It cannot contract. one just gets affected by ever more distant events. If the universe contracts enough, the visible universe becomes larger than the size of the universe and you can see the same object in more than one direction.

Yes my model has no such event horizon. Actually I don't think the total universe ever literally expands or contracts here. If half of it is "expanding" at some point in time then the other half of it should be contracting, and vica versa. I think that's why I originally wrote that the other half of the universe right now could be a black hole or black holes or some other concentrated mass. The universe's total simmetry is to be understood also across time, so one time slice of it may not look perfectly simmetrycal to us.

Atla wrote: ↑Tue Nov 19, 2024 5:05 am (So scratch what I wrote about there possibly being anti-versions of us right now in this time slice. (Unless if.. oh fuck I'll stop here.))

No-hair theorem says that there are only the three properties I listed. It's a theorem, meaning there's no debate about it. The contents of a black hole cannot effect the outside. In coordinate terms, all interior events are in the future of any outside events, and events in the future cannot affect past events, which would be backwards causality.

Yes "normally". But I'm talking about a finite but boundless universe in spacetime, so the past and future have to meet at a distant point in our past/future. Causality goes in a universal circle. And if you have a half-universe sized black hole colliding with a half-universe sized anti-matter black hole, not sure how much if any outside they have anymore. Besides black holes are thought to be able to evaporate too, and it could depend on whether or not quantum flucutations are truly random or only apparently random, whether or not that's an integral part of the universe's mechanics.

Atla wrote: ↑Tue Nov 19, 2024 5:05 am Oh fuck I give up this is too difficult. Too many unknowable parts.

Atla wrote: ↑Tue Nov 19, 2024 5:05 am I don't even think this is a good theory btw. A better explanation for dark energy might be that it's just antigravity. If other fundamental forces have both attractive and repulsive manifestations, then perhaps so should gravity. Dark energy created by the same things that have gravity.

Atla wrote: ↑Tue Nov 19, 2024 5:05 am

Yes, assuming the expansion is not accelerating. Even with infinite but not accelerating expansion, yes, you'd eventually come back to where you started. If there's acceleration, then there is an event horizon, and you can't go further than that.

You seem to be talking about going around in space, I was talking about going around in spacetime.

Atla wrote: ↑Tue Nov 19, 2024 5:05 am

If it's a hypersphere, then yes it does have to be curved. A torrid universe (like in asteroids video game) is finite, unbounded, and flat, but it's not spherical. So given that example, I agree with your statement.

I said "hyperspherical", to differentiate it from a literal hypersphere. I'm actually talking about a hyperspherical flat universe (and not just in space but also in time), but it's impossible to visualize it. Things like spheres and toruses are just geometrical concepts that may have nothing to do with the "shape" of the universe.

Noax wrote: ↑Tue Nov 19, 2024 6:35 am

Atla wrote: ↑Tue Nov 19, 2024 5:05 am Actually I don't think the total universe ever literally expands or contracts here.

Can't be a big bang without expansion.

Noax wrote: ↑Tue Nov 19, 2024 6:35 am

Atla wrote: ↑Tue Nov 19, 2024 5:05 am (So scratch what I wrote about there possibly being anti-versions of us right now in this time slice. (Unless if.. oh fuck I'll stop here.))

But I'm talking about a finite but boundless universe in spacetime, so the past and future have to meet at a distant point in our past/future.

Oh, you want time to be bounded and circular as well. Have fun with that.

A better explanation for dark energy might be that it's just antigravity.

Antigravity wouldn't be constant just like gravity isn't. But dark energy is constant energy density regardless of the change in the density of everything else as expansion occurs.

Noax wrote: ↑Tue Nov 19, 2024 6:35 am

Atla wrote: ↑Tue Nov 19, 2024 5:05 am You seem to be talking about going around in space, I was talking about going around in spacetime.

OK, you mean a spacelike worldline, not a timelike worldline of something travelling (moving through space). Sure, that can encircle the hypersphere even with accelerating expansion.

I said "hyperspherical", to differentiate it from a literal hypersphere. I'm actually talking about a hyperspherical flat universe (and not just in space but also in time), but it's impossible to visualize it.

I can visualize that, but it's still curved.

Things like spheres and toruses are just geometrical concepts that may have nothing to do with the "shape" of the universe.

But if you want a flat one, it's the way to go.

Noax wrote: ↑Tue Nov 19, 2024 6:35 am Oh, you want time to be bounded and circular as well. Have fun with that.

Can't be a big bang without expansion. The bang happens everywhere, not at some location. A finite size universe would have a tiny beginning that expands into what we see today.

Antigravity wouldn't be constant just like gravity isn't. But dark energy is constant energy density regardless of the change in the density of everything else as expansion occurs.

OK, you mean a spacelike worldline, not a timelike worldline of something travelling (moving through space). Sure, that can encircle the hypersphere even with accelerating expansion.

I can visualize that, but it's still curved.

Atla wrote: ↑Tue Nov 19, 2024 6:09 pm You're literally the first person I've met on a philosophy forum who understood the bounded and circular time concept (you did, right?).

Every other speculation I find illogical, and is therefore not interesting to me.

Also, the 2nd law of thermodynamics is a goner in my view

I even think that black holes probably do decrease entropy

Can't be a big bang without expansion. The bang happens everywhere, not at some location. A finite size universe would have a tiny beginning that expands into what we see today.

In that case, dark energy wouldn't be constant, but would appear as largely constant to us, as the dark energy of many galactic superclusters would roughly average out.

I don't think so, I'm talking about a spacetime worldline.

Noax wrote: ↑Wed Nov 20, 2024 1:32 am I think so, but wouldn't it be unbounded but finite circular time? Maybe I'm getting your wrong, because that sort of describes a cyclic model of a closed loop with a big bounce in it somewhere, and all very counterfactual and hard deterministic. There's also the Penrose closed cyclic model, but that one has unbounded time in both directions, no circle.

Am I not getting what you're envisioning?

Maybe, but something that accepts matter and returns it slowly as nothing but random radiation seems to be an increase of entropy to me.

I mean it's constant density over time, despite the expansion. Nothing else does that.