OT: Expanding universe question.

Excellent thought!

Reply to
Dan S. MacAbre
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If the space between objects in the universe were expanding, but not the objects, that would be reasonably descriptive. But if the entire universe and everything in it is expanding, well the ant would get bigger as well. So it breaks down...

Reply to
polygonum

Or do we exist in our own simulation?

Is that why we haven't detected aliens? Because THIS simulation was built by human subconscious for human needs, and doesn't include the concept of aliens in other dimensions, because we shut them out ?

Looking at many posters here, its perfectly clear they literally live in different worlds.

Reply to
The Natural Philosopher

Ah no. I think space is supposed to be expanding, but not whats in it.

Reply to
The Natural Philosopher

We don't know whether or not our universe's spacetime has periodic boundary conditions, but we do know that it extends far enough out from us that parts of it are forever unreachable.

The spacetime geometry of the universe might be periodic so that if you could travel fast enough you would come back to your starting point. But there is no way to tell experimentally if it is or not.

Reply to
Martin Brown

It would be helpful to know the answer to this one. Are things receding from each other because more space is somehow being created between them? Or is there some sort of 'fabric of the universe' whereby everything gets bigger? But if it's the latter, why does light seem to be immune to it, and become red-shifted? Or could it be that light just obeys laws of its own, and if it weren't for the red shift, there is absolutely no other physical way we could measure the expansion?

Reply to
Dan S. MacAbre

If that were the case how would we ever know?

Reply to
The Natural Philosopher

Well, that's what I'm wondering. If it weren't for the red shift, maybe we wouldn't? So many questions, so little time :-)

Reply to
Dan S. MacAbre

Welcome to the metaphysics of relativity.

We detect change....relative to what? Change on its own is not detectable if the detector is also changing along with it. in identical fashion.

And that is of course the core of the whole postmodern panic about - well everything really. Because we have no objective yardsticks left. Everything is relative to something else, we have along with God, destroyed the idea of Absolute reality, Absolute space, Absolute time, Absolute truth, Absolute morality.

And Quantum physics has pretty much destroyed the notion that the world is actually - well - the way we see it and smell it and touch it and feel it.

Its a bit like having spent your life watching a video screen, and suddenly unscrewing the back of it and finding out there weren't people in inside it and animals, just funny little transistors.

This has given rise to existential insecurities in the whole Western world. People grasp at straws like religion, sham science, or political correctness or socialism or new age crystal gazing - anything to find some objective fact to anchor their worldviews to.

Very few people are able to look the insecurity in the face and say 'oKAY...where does that leave us...?'

Reply to
The Natural Philosopher

I remembered where I got the idea that 'stuff' is expanding, too. I think most/many people realise that if there is all this space within atoms, then everything is actually almost completely space, and what se see/feel are just forces. So, if space 'out there' is said to be expanding, why not the space within? Unless there is something about the proximity of matter that prevents it? I really don't know.

Reply to
Dan S. MacAbre

Being raised protestant COE, I was able to dismiss God at a fairly early age with no unpleasant effects that I have yet been able to detect. My soul may be damned, but personally I need some proof before making profound commitments to religion. And, conveniently for them, religious types shun the notion of proof.

It does leave one feeling rather empty, though, but the 'why am I me, here, now' thing suggests we may get another go (what a waste, if not). I don't suppose it matters, though, because you don't get a recollection of your previous goes.

I'll never be able to understand quantum physics and cosmology, because I'm not much good with abstract concepts; but like Manuel might say 'I learn, Mister Fawlty, I learn!'. And it's usually interesting :-)

Staring into the abyss?

Reply to
Dan S. MacAbre

There are different forces of nature with widely different strengths acting over *very* different length scales.

In a handwaving description of the main actors in order of strength starting with the strongest as strength 1.

There is the strong nuclear force which binds together the internal quark components of protons and neutrons. Strength 1 Range 10^-15m

Electromagnetism and the photon Strength 1/137 Range Infinite

Weak nuclear force. Strength 10^-6 Range 10^-18m

Gravity Strength 6x10^-39 Range Infinite

Gravity is the odd one out in that it is so very much weaker compared to the others and is always attractive.

Reply to
Martin Brown

But that isn't what is happening. The universe is expanding and everything in it stays the same size. Strictly we can't tell that it isn't that the universe stays the same size and everything in it is shrinking but that variant requires a lot more "just so" coincidences.

It is more accurate to say that the distance between physical objects in the universe is getting bigger as a proportion of their separation. That was a *big* surprise when Hubble first observed it.

It was the first nail in the coffin of the prevailing Steady State theory of the day - microwave background being the final one.

Light isn't immune from it. The light is being also stretched along with the fabric of spacetime. It shows up as a redshift to longer wavelengths.

We are fairly sure that the laws of physics are the same throughout the universe and so measuring redshift is definitive. It was not always the case the Steady Staters fought a vigorous rearguard action against the new Big Bang theory (a derogatory term for it that Fred Hoyle first used) with Harp finding every oddball galaxy to try and discredit it.

Reply to
Martin Brown

Okay, thanks. I knew a (very) little about those. Seeing the static electricity from a comb overcome the gravity of the whole Earth (at least for small bits of paper) is fairly emphatic :-) I guess it means that there are forces holding us (and things) together that don't apply to the 'big' spaces in between.

Reply to
Dan S. MacAbre

So space (but only between 'things') is regarded as being 'stretched', rather than being 'made'.

I remember I borrowed a book from the school library in the 70's called 'Cosmology Now'. I didn't have much hope of understanding it, but I couldn't resist it. To my eternal shame, I keep it so long that I didn't dare return it, and no-one ever mentioned it. It's still around the house somewhere. It had contributions from various people, including Hermann Bondi, who was in the corner for the steady state theory. I remember him, because he had the first chapter, which I read more times than the others (you can guess that I struggled with it). And it's interesting that even then, they hadn't made their minds up about so much.

I see there's a copy on fleabay.

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I hadn't heard of any of these contributors at the time, but I have, of course, since then.

Hermann Bondi John Peach Martin Ryle Donald Lynden-Bell Dennis Sciama J.V. Narlikar W.H. McCrea Robert Penrose Martin Rees John Taylor Intro by Bernard Lovell

Reply to
Dan S. MacAbre

Don't forget that "things" are largely empty space anyway. Put a pea on the floor under the dome of St Pauls cathedral to represent the nucleus of an atom. Now look up at the dome. That's roughly where the atom's electrons would be for a very-much magnified atom. All the rest is empty space. And that's just one atom.

Reply to
Tim Streater

That's what I mentioned in another sub-thread (and what made me think we would be expanding too), but if what Martin says is correct (and I have absolutely no reason to doubt it), there are forces holding us together that don't apply out in space where there is no matter. Or something. I did know about these forces, and don't understand why they aren't subject to expansion (or, increases in scale), either. But the notion of things being made of 'nothing' /has/ been mentioned.

Reply to
Dan S. MacAbre

Coming up next: Popper, falsifiability and scientific proof.

Reply to
pamela

Brilliant. I could guess it was you, Turnip.

What's next? A polemic about cogito ergo sum?

Reply to
pamela

We have probably often seen the claim that everything expanded out from an incredibly dense, umm, pre-universe. Are you saying that every subatomic particle was at that time the same size as it now is? And that all that has happened is that they are further apart from each other? (Ignoring things like interconversion of energy and mass.)

Reply to
polygonum

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