How would we know the difference between an expanding universe and a collapsing one?

P

Parilyz

Registered Member
Disclaimer: I'm an amateur just looking for some insight.
Here's my idea I want to share:
Let's say that our universe was inside a black hole (I know, some other people have already started exploring this). If time or maybe space were being stretched inwards, if we were on the slope of the inward stretching space within, from our perspective, would the universe around us not appear as though it were expanding? How would we know? If space itself were stretching along an exponential curve inside said black hole, would we be able to use any kinds of observations to differentiate from an expanding universe? Could each black hole be a 'house' for new universes? Could the 'everything' (not sure if it should be called a dimension, might be the wrong word) be an infinite amount of universes inside black holes residing in subsequent universes? Like those Russian dolls, but infinite in either direction? I often think of fractal patterns found in nature and it makes me wonder if the universe itself and it's subsequent construction is not like the Mandelbrot - that we could 'zoom in' to a black hole, find another universe that had it's own black holes just like we see in our universe, and repeat down the 'zoom line' forever?
 
Parilyz said:
Disclaimer: I'm an amateur just looking for some insight.
Here's my idea I want to share:
Let's say that our universe was inside a black hole (I know, some other people have already started exploring this). If time or maybe space were being stretched inwards, if we were on the slope of the inward stretching space within, from our perspective, would the universe around us not appear as though it were expanding? How would we know? If space itself were stretching along an exponential curve inside said black hole, would we be able to use any kinds of observations to differentiate from an expanding universe? Could each black hole be a 'house' for new universes? Could the 'everything' (not sure if it should be called a dimension, might be the wrong word) be an infinite amount of universes inside black holes residing in subsequent universes? Like those Russian dolls, but infinite in either direction? I often think of fractal patterns found in nature and it makes me wonder if the universe itself and it's subsequent construction is not like the Mandelbrot - that we could 'zoom in' to a black hole, find another universe that had it's own black holes just like we see in our universe, and repeat down the 'zoom line' forever?
Click to expand...
We know our universe is expanding by observations of distant galaxies, standard candles within those galaxies and also the CMBR.
Current consensus is that our Universe is 13.8 billion years old and is spatially infinite.
In 1998 it was discovered that the rate of acceleration was increasing and in the last few weeks it looks like the Cosmological constant is probably not a constant.
It is estimated that the entire universe is much larger than the observable universe.
IF all of that is happening inside a black hole, how could we tell?
 
Parilyz said:
Disclaimer: I'm an amateur just looking for some insight.
Here's my idea I want to share:
Let's say that our universe was inside a black hole (I know, some other people have already started exploring this). If time or maybe space were being stretched inwards, if we were on the slope of the inward stretching space within, from our perspective, would the universe around us not appear as though it were expanding? How would we know? If space itself were stretching along an exponential curve inside said black hole, would we be able to use any kinds of observations to differentiate from an expanding universe? Could each black hole be a 'house' for new universes? Could the 'everything' (not sure if it should be called a dimension, might be the wrong word) be an infinite amount of universes inside black holes residing in subsequent universes? Like those Russian dolls, but infinite in either direction? I often think of fractal patterns found in nature and it makes me wonder if the universe itself and it's subsequent construction is not like the Mandelbrot - that we could 'zoom in' to a black hole, find another universe that had it's own black holes just like we see in our universe, and repeat down the 'zoom line' forever?
Click to expand...
Yes, I think Pinball1970 's "How could we tell?" point is what divides science from metaphysical speculation. I suppose it's a matter of aesthetic preference, really, whether one wants to imagine such possibilities or whether one decides to stick to what can be inferred from observable phenomena. In particle physics, string theory is a bit the same, suffering from the drawback that none of its speculations seem to lead to any means of being tested to see if nature is really like that or not. Some people are drawn to the idea of multiple universes as a way of dealing with the issue of why the physical constants (in our universe, as it were) have the values they do, since one could envisage a whole series of universes exploring all the possible permutations of values for them. (Personally, I'm not persuaded this is a problem.)

I don't know enough about cosmology to comment in detail on your idea about "inward stretching" of space, though. Has not Carlo Rovelli gone into this a bit?
 
Parilyz:
Parilyz said:
Here's my idea I want to share:
Let's say that our universe was inside a black hole (I know, some other people have already started exploring this).
Click to expand...
If that were the case, then everything in the universe would be moving inexorably towards the centre of the hole. Instead, we see the universe expanding in all directions.
Parilyz said:
If time or maybe space were being stretched inwards, if we were on the slope of the inward stretching space within, from our perspective, would the universe around us not appear as though it were expanding?
Click to expand...
If a black hole has constant mass, the spacetime around it is essentially static. It does not "stretch". Unless I'm misunderstanding what you mean, perhaps. What do you actually mean?
Parilyz said:
If space itself were stretching along an exponential curve inside said black hole, would we be able to use any kinds of observations to differentiate from an expanding universe?
Click to expand...
Why would space stretch inside a black hole? What would cause the stretching? You'd need to add or subtract mass, wouldn't you?
Parilyz said:
Could each black hole be a 'house' for new universes?
Click to expand...
Who knows? Do you think it could be? If so, why? I'm not sure what "a 'house' for new universes" even means.
Parilyz said:
Could the 'everything' (not sure if it should be called a dimension, might be the wrong word) be an infinite amount of universes inside black holes residing in subsequent universes?
Click to expand...
Black holes all have finite mass. Infinite universes, on the other hand, would have infinite mass.
Parilyz said:
I often think of fractal patterns found in nature and it makes me wonder if the universe itself and it's subsequent construction is not like the Mandelbrot - that we could 'zoom in' to a black hole, find another universe that had it's own black holes just like we see in our universe, and repeat down the 'zoom line' forever?
Click to expand...
Imagination is all well and good, but at some point the rubber has to hit the road. Is there any physical theory that you're aware of which suggests that what you imagine could actually be the case? Or are you just tossing the idea out there to see if somebody else can make some sense of it?
 
James R.:

dd we are try to engineer the sneqier 7

Yeah, this should purchase me a life-time membership herein.
 
Moderator note: Mr. G has been warned for off-topic posting, and more generally for just cluttering up threads with valueless posts.

Due to accumulated warning points, we won't be seeing him again for a couple of weeks, at least.
 
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