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Event Horizons musings

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chasmanian
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Event Horizons musings

#1

Post by chasmanian » Sun Jan 12, 2020 4:56 am

nFA said something in a recent thread that caught my attention,
intrigues me and fires my imagination.

the event horizons surrounding black holes,
of which there may be billions, I have no idea,
and the event horizon that is surrounding our Universe,
(beyond which it is expanding faster than the speed of light),
are exactly the same.

I would like to compare and contrast the 2 event horizons.

maybe there's really not much more to it.
but maybe there is.
for example, is the event horizon beyond which the Universe is expanding faster than light,
moving away from us?
and therefore getting larger, and farther away all the time?
I would think that it must be.
and that the part of the Universe that already is moving faster than light, just keeps moving faster and faster.

also, think about how the speed of light is related to both kinds of event horizons.

and the Universe event horizon, is sort of like an inside out or opposite in a way,
compared to the black hole event horizons which enclose a space.

both event horizons close us off from information.

the Universe event horizon is like an expanding bubble.

nFA, where is the Universe event horizon with respect to the Observable Universe?
are they at the same place, or near each other?

also, I am sure that the Universe event horizon's location will vary with the observer's location.

thats all I can think of for now.
any thoughts, guys and gals?
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#2

Post by notFritzArgelander » Sun Jan 12, 2020 6:31 am

chasmanian wrote:
Sun Jan 12, 2020 4:56 am
nFA said something in a recent thread that caught my attention,
intrigues me and fires my imagination.

the event horizons surrounding black holes,
of which there may be billions, I have no idea,
and the event horizon that is surrounding our Universe,
(beyond which it is expanding faster than the speed of light),
are exactly the same.
Interesting question. But to get things off right let me pause here to comment. The large event horizon doesn't surround our universe. The universe extends beyond it.

Remember that per the Planck data the CMB indicates that the universe is flat and infinite in extent. So there is no surrounding it. Rather the big event horizon you are thinking of is the limit of the observable universe.
I would like to compare and contrast the 2 event horizons.

maybe there's really not much more to it.
but maybe there is.
for example, is the event horizon beyond which the Universe is expanding faster than light,
moving away from us?
and therefore getting larger, and farther away all the time?
I would think that it must be.
and that the part of the Universe that already is moving faster than light, just keeps moving faster and faster.
It depends on whether there is dark energy or not actually and also a few other details. I'm going to base my remarks on the Standard Model of Cosmology, the ΛCDM (Lambda cold dark matter) model, nothing exotic or magical.

https://en.wikipedia.org/wiki/Lambda-CDM_model

https://en.wikipedia.org/wiki/Friedmann_equations

I'm going to talk in terms of distances like the usual rulers and not comoving coordinate distances, which introduce interesting complications. Maybe another post.

In a universe where the Hubble constant is truly constant what you say is true. The event horizon that bounds the observable universe keeps getting further and further away. This is simply due to the fact that will a longer elapsed age of the universe we can see further into it. Simple.

But the Hubble constant is NOT time independent. It varies with the age of the universe itself.

Part of this variability is due to the mass energy content of the universe. The Friedman equations show that the mass energy content of the universe causes the Hubble "constant" to decrease over time. This will cause the radius at which separations exceed the speed of light to increase FASTER than the look back time effect. So qualitatively speaking, the observable universe's event horizon still expands.

What throws a spanner in the works is dark energy. Dark energy causes the Hubble "constant" to INCREASE over time. So that would cause the radius (ruler distance) to the event horizon to decrease! If H0 increases then the distance to the light speed radius decreases.

So whether the distance to the observable universe event horizon increases or decreases depends on the numbers: how does the initial value of H0 get modified by the mass energy content of the universe (decreasing it) or by dark energy (increasing it).

If dark energy is stronger than a cosmological constant value then eventually the event horizon comes rushing toward you in a Big Rip and you get spaghettified along the way. https://en.wikipedia.org/wiki/Big_Rip But I said I wasn't going to discuss non standard cosmologies so I'll just mention it and leave it alone.
also, think about how the speed of light is related to both kinds of event horizons.

and the Universe event horizon, is sort of like an inside out or opposite in a way,
compared to the black hole event horizons which enclose a space.

both event horizons close us off from information.

the Universe event horizon is like an expanding bubble.
Also they are similar in that in both cases the local inertial reference frames are moving faster than the speed of light on just the other side.
nFA, where is the Universe event horizon with respect to the Observable Universe?
are they at the same place, or near each other?
the universe's event horizon IS the boundary of the observable universe. there is a distinction in name only. physically they are identical.
also, I am sure that the Universe event horizon's location will vary with the observer's location.
yes. every observer sees the universe's event horizon (the radius of the Observable Universe) at the same distance away.

one last mention of a non standard cosmology. in ECSK gravity every little BH event horizon is the place of birth of a new universe and the radius of the Observable Universe is where ours was born. so in ECSK the distinction between these two kinds of event horizons utterly disappears.
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#3

Post by chasmanian » Sun Jan 12, 2020 4:51 pm

thank you so much nFA.
will reply again soon.
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#4

Post by chasmanian » Sun Jan 12, 2020 11:37 pm

nFA,
would you please say more about this?:

"Also they are similar in that in both cases the local inertial reference frames are moving faster than the speed of light on just the other side."

what does this mean about the interior of Black Holes?
(I think I understand that for the Universe Event Horizon, it does not violate SR.
thats because, SR allows for exceeding the SOL,
when its caused by the expansion of space.
but I do not understand how this applies to Black Holes. they are very strange things.)

"in ECSK gravity every little BH event horizon is the place of birth of a new universe and
the radius of the Observable Universe is where ours was born."

so could we say that we live inside a sort of inside out Black Hole? :)
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#5

Post by notFritzArgelander » Sun Jan 12, 2020 11:56 pm

chasmanian wrote:
Sun Jan 12, 2020 11:37 pm
nFA,
would you please say more about this?:

"Also they are similar in that in both cases the local inertial reference frames are moving faster than the speed of light on just the other side."

what does this mean about the interior of Black Holes?
(I think I understand that for the Universe Event Horizon, it does not violate SR.
thats because, SR allows for exceeding the SOL,
when its caused by the expansion of space.
but I do not understand how this applies to Black Holes. they are very strange things.)
Indeed. Under the event horizon the roles of the watch and a radially directed meter stick are reversed (as computed by a distant observer). A locally inertial observer's velocity is faster than light. Space rushes toward the center.
Inside the event horizon

"in ECSK gravity every little BH event horizon is the place of birth of a new universe and
the radius of the Observable Universe is where ours was born."

so could we say that we live inside a sort of inside out Black Hole? :)
In ECSK that would be the same as living inside a White Hole.
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#6

Post by chasmanian » Mon Jan 13, 2020 3:12 am

ah cool!!

thanks nFA!!!

"Under the event horizon the roles of the watch and a radially directed meter stick are reversed (as computed by a distant observer). A locally inertial observer's velocity is faster than light. Space rushes toward the center."

if it strikes your fancy, would you please elaborate on that?
not quite following you here with regards to the role reversal.

also, as space rushes towards the center, do we hypothesize that it gets more dense?
its the opposite of expanding space, methinks. so its compressing we might say?

and a locally inertial observer inside the black hole would be moving towards the center faster than light?
then wouldn't they get to the center in no time flat? hahahahahhaha

and another contrast between the 2 kinds of event horizons, would perhaps be that
inside the black hole event horizon, space is compressing?
and outside the Universe event horizon, space is expanding?
(although both at or faster than the SOL?)
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#7

Post by notFritzArgelander » Mon Jan 13, 2020 5:24 am

chasmanian wrote:
Mon Jan 13, 2020 3:12 am
ah cool!!

thanks nFA!!!

"Under the event horizon the roles of the watch and a radially directed meter stick are reversed (as computed by a distant observer). A locally inertial observer's velocity is faster than light. Space rushes toward the center."

if it strikes your fancy, would you please elaborate on that?
not quite following you here with regards to the role reversal.

also, as space rushes towards the center, do we hypothesize that it gets more dense?
its the opposite of expanding space, methinks. so its compressing we might say?
We're inside an event horizon so it's hard to say. One cannot formulate an experiment for us folks outside the event horizon. The theoretical problem of what an inside observer would see is problematic and an object of current research. Carlo Rovelli (who unlike yours truly is no slacker or sloucher) says that the interior volume of a BH is constantly expanding!

https://arxiv.org/abs/1411.2854
The 3d volume inside a spherical black hole can be defined by extending an intrinsic flat-spacetime characterization of the volume inside a 2-sphere. For a collapsed object, the volume grows with time since the collapse, reaching a simple asymptotic form, which has a compelling geometrical interpretation. Perhaps surprising, it is large. The result may have relevance for the discussion on the information paradox.
There is also discussion on this point at https://www.physicsforums.com/threads/i ... le.962341/

So let's wait and see how the smart folks sort it out. :)

As for the switching of watches and meter sticks that follows from the sign change in the metric coefficients in the Schwarzschild metric.

The authors of this article have chosen a sign convention such that a negative coefficient is the timelike and a positive coefficient is spacelike. https://en.wikipedia.org/wiki/Schwarzschild_metric Once you duck inside the Schwarzschild radius rs the terms for time and radius swap signs. So in the distant observers frame watches become meter sticks and meter sticks become watches.
[and a locally inertial observer inside the black hole would be moving towards the center faster than light?
then wouldn't they get to the center in no time flat? hahahahahhaha
It turns out that the inside observer just gets to the center (his watch is still a watch) in a finite time. But every effort made to avoid colliding with the center hastens his arrival.
and another contrast between the 2 kinds of event horizons, would perhaps be that
inside the black hole event horizon, space is compressing?
and outside the Universe event horizon, space is expanding?
(although both at or faster than the SOL?)
But according to Rovelli both spaces on the other side of the event horizon are expanding. :)
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#8

Post by chasmanian » Mon Jan 13, 2020 4:17 pm

thank you nFA!!

amazing, wow!! all you posted.

as for time and space interchangable-ness,
I have a foggy memory now about,
describing reference frames where perhaps:
for 2 observers,
some of my time, is your space and vice versa.
its the whole spacetime blend of space and time as 1 thing,
compared to the Newtonian view of space and time as separate thingies. :)
(and I propose that thingies should be an official Astrophysics term! hahahaha)
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#9

Post by chasmanian » Tue Jan 14, 2020 5:14 am

nFA,

I was just having some fun thinking about some things.

on the other side of the Universe event horizon, I am guessing there are some Black Holes.
and at first I was thinking about
what it would be like for them to be in a place where space is expanding faster than light.
how would that affect those Black Holes event horizons?
and then it occurred to me that maybe I'm wrong.
space over there, from their local perspective is not expanding faster than light.
in fact now that I think more about it,
maybe from their perspective, our space here is expanding faster than light?
any thoughts about this?

next, about Rovelli and the expanding volume inside Black Holes.
a tad counterintuitive, no? ouch, where's my aspirin!! :)
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#10

Post by notFritzArgelander » Tue Jan 14, 2020 5:41 am

chasmanian wrote:
Tue Jan 14, 2020 5:14 am
nFA,

I was just having some fun thinking about some things.

on the other side of the Universe event horizon, I am guessing there are some Black Holes.
and at first I was thinking about
what it would be like for them to be in a place where space is expanding faster than light.[/url]

it would be the same as being where we are. the universe is homogenous and isotropic. so they don't see things expanding quickly unless they are very far away. just like here.
how would that affect those Black Holes event horizons?
and then it occurred to me that maybe I'm wrong.
space over there, from their local perspective is not expanding faster than light.
in fact now that I think more about it,
maybe from their perspective, our space here is expanding faster than light?
any thoughts about this?
exactly so. the universe is homogenous and isotropic AFAWK.
next, about Rovelli and the expanding volume inside Black Holes.
a tad counterintuitive, no? ouch, where's my aspirin!! :)
it all depends on the reference frame, no? from "out here" we can't measure the interior volume of a BH. but an observer inside one can measure it. i think that's how it works but i'd have to read up again to be sure.
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#11

Post by chasmanian » Wed Jan 15, 2020 4:29 am

thank you nFA!! :)

"so could we say that we live inside a sort of inside out Black Hole? :)"

"In ECSK that would be the same as living inside a White Hole."

I just had another thought regarding this.

imagine an observer that is on the other side of the Universe event horizon.
ok, now imagine that they are the same distance away as we are from the Universe event horizon,
(continuing away from us.)
that is to say, that our Universe event horizon at one point, is their's too.
at that one point, we share the Universe event horizon.

ok, so here we are at the center of our White Hole. and the other observer is at the center of their White Hole.
and you could continue on from there to the next White Hole and the next.
and now the fun really starts, because,

we could say the same thing in any direction.
its infinite White Holes in every direction.
and its turtles all the way down.
and just for kicks, all of these White Holes have hundreds of billions of Black Holes in them.
what do you think, nFA?
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#12

Post by notFritzArgelander » Wed Jan 15, 2020 6:56 am

chasmanian wrote:
Wed Jan 15, 2020 4:29 am

I just had another thought regarding this.

imagine an observer that is on the other side of the Universe event horizon.
ok, now imagine that they are the same distance away as we are from the Universe event horizon,
(continuing away from us.)
that is to say, that our Universe event horizon at one point, is their's too.
at that one point, we share the Universe event horizon.
yes, only at that one point would the event horizons be shared.
ok, so here we are at the center of our White Hole. and the other observer is at the center of their White Hole.
and you could continue on from there to the next White Hole and the next.
and now the fun really starts, because,
what is the meaning of "center of a White Hole"? i fear i have misled you. i apologize. the event horizon at the edge of the observable universe cannot be identified with the event horizon in ECSK of the parent black hole that birthed this universe.

i made the error in post #2 where i said "in ECSK gravity every little BH event horizon is the place of birth of a new universe and the radius of the Observable Universe is where ours was born."

that's just wrong. in ECSK the event horizon of a BH gives birth to a White Hole and whatever pieces in it are limited by an event horizon for a particular observer are completely independent of the birthing event horizon.

so......
we could say the same thing in any direction.
its infinite White Holes in every direction.
and its turtles all the way down.
no turtles in that sense.
and just for kicks, all of these White Holes have hundreds of billions of Black Holes in them.
what do you think, nFA?
i think that with the above misidentification of the event horizon at the radius of the observable universe with the originating horizon removed, there are no turtle towers.

but it is a very peculiar slab of swiss cheese.

another way to put it is to use the wormhole idea. in ECSK every BH is a tunnel to a different universe.
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#13

Post by chasmanian » Thu Jan 16, 2020 4:16 am

thank you for all you wrote nFA.
I super appreciate every word.

also, I was not thinking about your post #2 at all in my recent posts.

I was thinking about a recent thread where I think you said that
the event horizon of a black hole and the event horizon surrounding our Universe are the same thing.

here's more of my musings.
we are on the outside of the black hole event horizon.
but we are on the inside of the Universe edge event horizon.

I am enjoying the thought that they are the same thing.

inside of a black hole, something is happening that is faster than SOL.

on the other side of the Universe event horizon, space is expanding faster than SOL
wow, cool!!! :)

I do understand now, how that faster than SOL expansion of space depends upon us being very far away,
like 46 billion light years away.
where as the faster than SOL Black Hole stuff does not require any such thing.

as for ECSK, hmmm.
I was only thinking about your post #5 reply to me asking:

"so could we say that we live inside a sort of inside out Black Hole? :)"


and you said:
"In ECSK that would be the same as living inside a White Hole."

I now will google and see what I can find out about ECSK and White Holes.

thank you again for all of your excellent amazing replies. :)
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#14

Post by notFritzArgelander » Thu Jan 16, 2020 6:02 am

OK very good. now for icing on this cake... event horizons are not real physical objects, they are artifacts of the choice of coordinate system.
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#15

Post by chasmanian » Thu Jan 16, 2020 7:00 pm

wow, ok very good.
thank you nFA. :)
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