Cosmology

[roubaixtuesday]

A thread to explore our universe, born from a thread on Ghosts.

First: the Big Bang - the universe is expanding, but what is it expanding into?

Answer: it's not a meaningful question.

Following from

https://bigthink.com/starts-with-a-bang ... ding-into/

Specially for @reohn2

When it comes to the expanding Universe, it isn’t expanding into anything, because there isn’t anything else above, beyond, outside, or before or after space-and-time. All at once, it’s both everything and nothing: everything because it contains all that exists, and nothing because if you take all the matter, radiation, and quanta that exist within it away, it still persists: the nothingness of empty space itself. That’s what the fabric of spacetime is, and that’s why it can’t expand “into” anything: it itself is a fundamental part of our reality.

That’s why, when you ask, “What is the Universe expanding into?” the best answer we can give is “itself.” The key realization is to stop thinking of the Universe as a thing that evolves in some larger, greater context; it’s perfectly reasonable to think of it as all there is, and to simply recognize that expansion and contraction are properties inherent to space itself.

[roubaixtuesday]

And an image to inspire, taken in infra red light by the James Webb space telescope.

Not only an awe inspiring image, every galaxy here having around 100 billion stars, which emitted their light billions of years ago, but it also visually shows the fabric of spacetime being deformed by the force of gravity.

From https://webbtelescope.org/contents/medi ... 5CSH1Q5Z1Z

[[XAP]Bob]

visually shows the fabric of spacetime being deformed by the force of gravity.

Just to be clear - the curved lines are *really* distant galaxies whose light has been bent (lensed) around other massive objects (galaxies) between us and the really distant galaxy.

That curve isn't an artefact of the camera, it's what happens to light passing through a galactic cluster style lens (i.e. the massive object in question here isn't a single galaxy, but a cluster of them). different image shapes are caused by different objects acting as gravitational lenses.

[mattheus]

visually shows the fabric of spacetime being deformed by the force of gravity.

Just to be clear - the curved lines are *really* distant galaxies whose light has been bent (lensed) around other massive objects (galaxies) between us and the really distant galaxy.

That curve isn't an artefact of the camera, it's what happens to light passing through a galactic cluster style lens (i.e. the massive object in question here isn't a single galaxy, but a cluster of them). different image shapes are caused by different objects acting as gravitational lenses.

Just amazing!

[peetee]

While I don’t pretend to have the intellect of Isaac Newton I am, just as he was, occasionally struck motionless by a mind-bending exploration of a principle or theory. The greatest of these happened one day around 6am when I woke too early to get up and start the day and too late to contemplate sleep. Anyhow, I digress. I can’t say exactly how I came to the following conclusion but the journey made perfect sense and the conclusion still does - insomuch as it rounds off the whole ‘where did we come from & where are we going’ debate.
So, in a nutshell, here it is,
Space time is spherical.
The universe is expanding, its expansion is relative to time. Time and the space the universe occupies is governed by the cosmological constant - that being gravity. Gravity is merely the universal attraction of matter. As long as there is matter there will be attraction as long as there is matter there will be time. That is the basis of all matter and that shape is always spherical, ergo space/time is spherical. Time prescribes a linear path around gravity and in terms of matter that path expands and contracts. Matter and the space it occupies follows a linear path but space/time dictates that path expands away from a singularity and contract towards the next as if following the surface of a sphere. The ‘big bang’ is simply the appearance of matter following this path from the perspective of beings governed by comprehension and experiences of space within time.
This explaination is, I admit, compromised by the need to translate my thoughts into words, that being a skill I would be the first to admit is weak at best.
There are huge holes in this argument, the biggest of which being my use of the term ‘gravity’ to explain the core of space/time ie that which the universe is travelling around, through the medium of time. It could be that the gravity we know is not the same and this cosmological constant is governed by dark matter.
Until my next ‘episode’ we will have to leave it there.
Oh, and if you have got this far, thanks for your patience, or, depending upon your point of view ‘Don’t Panic’

[[XAP]Bob]

‘where did we come from & where are we going’ debate.

Cotton Eye Joe...

[reohn2]

A thread to explore our universe, born from a thread on Ghosts.

First: the Big Bang - the universe is expanding, but what is it expanding into?

Answer: it's not a meaningful question.

Following from

https://bigthink.com/starts-with-a-bang ... ding-into/

Specially for @reohn2

When it comes to the expanding Universe, it isn’t expanding into anything, because there isn’t anything else above, beyond, outside, or before or after space-and-time. All at once, it’s both everything and nothing: everything because it contains all that exists, and nothing because if you take all the matter, radiation, and quanta that exist within it away, it still persists: the nothingness of empty space itself. That’s what the fabric of spacetime is, and that’s why it can’t expand “into” anything: it itself is a fundamental part of our reality.

That’s why, when you ask, “What is the Universe expanding into?” the best answer we can give is “itself.” The key realization is to stop thinking of the Universe as a thing that evolves in some larger, greater context; it’s perfectly reasonable to think of it as all there is, and to simply recognize that expansion and contraction are properties inherent to space itself.

An acceptable explanation to my mind.Thanks.

[simonineaston]

In space, no one can hear your bicycle bell...

[[XAP]Bob]

In space, no one can hear your bicycle bell...

Partly because it's still on earth...

[pwa]

So let me get this right. When you reach the furthest limits of the Universe (capital U because it is a place name) and all that is left is Nothing, a void or emptiness, beyond that would be No Nothing. What would it be like to look in the direction of No Nothing, I wonder. Possibly a bit like Swansea on a wet day, I expect.

[roubaixtuesday]

So let me get this right. When you reach the furthest limits of the Universe (capital U because it is a place name) and all that is left is Nothing, a void or emptiness, beyond that would be No Nothing. What would it be like to look in the direction of No Nothing, I wonder. Possibly a bit like Swansea on a wet day, I expect.

Per previous answers, this is not a meaningful question.

In the same way that you can't look over the edge of the world.

[deeferdonk]

There are billions of universes expanding like bubbles in an infinite glass of prosecco being drunk by God.

[[XAP]Bob]

So let me get this right. When you reach the furthest limits of the Universe (capital U because it is a place name) and all that is left is Nothing, a void or emptiness, beyond that would be No Nothing. What would it be like to look in the direction of No Nothing, I wonder. Possibly a bit like Swansea on a wet day, I expect.

What does the furthest limit of the universe even mean?
We know where the edge of the *observable* universe is, but that's not an edge in any way other than "from our view"

Note that JADES-GS-z13-0 (a galaxy detected with JWST) is 33.6 billion light years away, the light has travelled for ~13.5 billion years to get to u, but the space has expanded while it's been travelling...


The concept of "not even nothing" is odd, because it's *so* far outside of our experience. There is always space into which something expands - but in this case it's space itself which is expanding, and that's very weird.

[roubaixtuesday]

The concept of "not even nothing" is odd, because it's *so* far outside of our experience. There is always space into which something expands - but in this case it's space itself which is expanding, and that's very weird.

I think the first thing to do when thinking about cosmology, quantum physics and other branches of science outside of our normal experience is to let go of what is weird or odd.

It's all weird and odd, and defies our day to day experience and senses. Trying to apply them to it dooms us to immediately failing to grasp the most basic concepts.

[[XAP]Bob]

Absolutely - Neither cosmological nor quantum scales map onto human experience.

You can do some simple astrophysics with "experience led" intuition, but it falls apart very rapidly - and I tried to stay away from physics modules marked with a T during my degree.
T was for Torture, or maybe Theoretical