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The universe is expanding faster than expected

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Re: The universe is expanding faster than expected

#171

Post by macintux »

bouncycastle wrote: post #166
dheera wrote: post #147

Earlier quoted context omitted.

The biggest "concern" I have about the expanding universe is that although I have a lot of hope for interstellar travel at some point in the coming few millenia, intergalactic travel poses a whole another set of impossibilities to face, that I'm worried it will never be possible. The space between galaxies is pretty devoid of anything you can use as fuel, repair materials, or anything else. That space is expanding, a…

However, after the universe finishes expanding, wouldn't it start contracting again? Btw, Andromeda will collide with the Milky Way in about 4 billion years, so at least we won't need ten times the mass of Mt. Everest to get there...

> However, after the universe finishes expanding, wouldn't it start contracting again?

Unless the answer has changed in the last several years, no, the consensus is that it's expanding too fast and has too little mass (and thus gravity) to collapse again.

(Disclaimer: not even an amateur at this, at least not for 40 years.)

Re: The universe is expanding faster than expected

#172

Post by johnnujler »

Forgive my ignorance here. What do we mean when we say the universe is expanding, expanding into what. My untrained brain is trying to look at it like the inflation of a balloon that takes up more space when it is inflated, but if the universe is all the space there is, what would it even mean for it to expand. Is there space outside our universe that is like unfilled or something?

Re: The universe is expanding faster than expected

#173

Post by ellis-bell »

johnnujler wrote: post #172

Forgive my ignorance here. What do we mean when we say the universe is expanding, expanding into what. My untrained brain is trying to look at it like the inflation of a balloon that takes up more space when it is inflated, but if the universe is all the space there is, what would it even mean for it to expand. Is there space outside our universe that is like unfilled or something?

think more like you're on the surface of the balloon as it's getting inflated. the "fabric" or elastic material on which you're standing is the thing that's expanding while the balloon inflates. you're still constrained to the surface of the balloon, however.

Re: The universe is expanding faster than expected

#174

Post by pdonis »

grishka wrote: post #156
pdonis wrote: post #115

Earlier quoted context omitted.

> It would indeed be incredibly exciting if it would lead to a less silly explanation of the redshift than "universe is expanding". It won't. There is no question about whether the universe is expanding. The issue is over how fast it is expanding; we have two different theoretical models that are giving different answers, and we don't understand (yet) how to reconcile them.

> There is no question about whether the universe is expanding. Why? > we have two different theoretical models that are giving different answers, and we don't understand (yet) how to reconcile them. Maybe... just maybe... that's because it isn't actually expanding, but there's some other, unknown effects at play? It's about time we think outside the box. To me, as a regular programmer kind of person, the very idea t…

> It's about time we think outside the box

Another way of looking at it, to add to my previous post: dark matter and MOND are thinking outside the box. They cover both possibilities for how to expand on our current theories: either (a) there's more "stuff" out there than our current theories of particle physics know about; or (b) there's more aspects to gravity than our current theory of gravity knows about. Consider whatever "unknown effects" you like: they will end up coming down to one of those two possibilities.

Thinking "inside the box" would be something like: it's far more likely that either the data is wrong or we haven't calculated the predictions of our current theories correctly than that our current theories, which have tons of experimental confirmation, are wrong. Historically, most of the time in science, when there's been a discrepancy between theories and data, that is how the discrepancy has ended up being resolved: either we've figured out something was wrong with the data, or we've figured out that something was wrong with how we calculated the predictions of our current theories.

The reason why cosmologists are driven to consider models like dark matter and MOND is that they have checked and double checked and triple checked both the data and our predictions from our current theories, and the mismatch hasn't gone away. So they are driven to consider "out of the box" ideas, and, as above, dark matter and MOND cover the possibilities.

Re: The universe is expanding faster than expected

#175

Post by cstejerean »

johnnujler wrote: post #172

Forgive my ignorance here. What do we mean when we say the universe is expanding, expanding into what. My untrained brain is trying to look at it like the inflation of a balloon that takes up more space when it is inflated, but if the universe is all the space there is, what would it even mean for it to expand. Is there space outside our universe that is like unfilled or something?

You can look at it the other way. Ignore for a moment the surface of the balloon and imagine the insides. As the balloon expands everything inside gets farther from everything else. That’s how I understand the universe expanding.

Re: The universe is expanding faster than expected

#176

Post by vecter »

johnnujler wrote: post #172

Forgive my ignorance here. What do we mean when we say the universe is expanding, expanding into what. My untrained brain is trying to look at it like the inflation of a balloon that takes up more space when it is inflated, but if the universe is all the space there is, what would it even mean for it to expand. Is there space outside our universe that is like unfilled or something?

Your balloon analogy is almost correct but it's missing one important piece. In that analogy, the surface of the balloon itself is the entire universe. It is a two-dimensional universe. Imagine that there is no other space except for that surface of the balloon. No emptiness inside and no space outside that it's "expanding into".

The entire space is the infinitesimally thin surface which is the balloon surface, yet it is still expanding. Dots on that surface that used to be X distance apart are now > X distance apart in the future. That is all you would know and be able to measure.

Re: The universe is expanding faster than expected

#177

Post by pdonis »

gpderetta wrote: post #139
mpoteat wrote: post #125

Earlier quoted context omitted.

Not a physicist, but why isn't the simple explanation that light loses energy over cosmological distances not also a valid explanation of redshift? We already know that energy isn't conserved at those scales.

Energy is not conserved at those scales because of general relativity, which also provides the mechanism for an expannding universe. Einstein himself didn't like this result of GE and tried to hack around it with the cosmological constant. Turns out the math was right.

> Turns out the math was right.

Actually, turns out the math was right with a cosmological constant: that's how the accelerating expansion of our universe is explained. Einstein actually blundered twice: first by putting in the constant for the wrong reason (because he wanted a static universe), but then taking it out again when it turned out that reason wasn't the case (when the expansion of the universe was discovered).

If you just look at how to derive the Einstein Field Equation of General Relativity from first principles, the constant should be there; it isn't an add-on to General Relativity at all, it's part of it. It's just that there's no way to know from those first principles what its value is. That we had to figure out from observations.

Re: The universe is expanding faster than expected

#178

Post by systemvoltage »

dheera wrote: post #147
7373737373 wrote: post #5

Here's a narrated video about this current cosmological crisis: https://www.youtube.com/watch?v=0sfvQ_fsil4 This is one of the key graphics: https://i0.wp.com/particlebites.com/wp-content/uploads/2020/...

The biggest "concern" I have about the expanding universe is that although I have a lot of hope for interstellar travel at some point in the coming few millenia, intergalactic travel poses a whole another set of impossibilities to face, that I'm worried it will never be possible. The space between galaxies is pretty devoid of anything you can use as fuel, repair materials, or anything else. That space is expanding, a…

500 years from now - a shockingly small slice of time in the history of human evolution, our understanding of the universe has changed a lot. Folks, if you’re reading this from the future - we are currently mostly clueless but have made some solid progress. GIFs load 10x faster than they did just 10 years ago! This virus thing has been a real pain in the ass though.

Re: The universe is expanding faster than expected

#179

Post by vecter »

drukenemo wrote: post #143
chanakya wrote: post #126

Can someone explain why the universe is expanding at all? I've heard it said "it's the momentum from the Big Bang". That sounds reasonable, but then we're told that it's not that the galaxies are flying apart, it's that the "basic metric of space itself is expanding". I can understand momentum from an explosion, but why would "space itself" expand because of an explosion?

I’m amazed how the God hypothesis seems to not exist amongst the modern, smart tech world. Everything is science, science one day will know...

That's because it violates Occam's razor. That doesn't disprove the existence of a God, of course, but it makes it less likely if you accept Occam's razor to some degree.

The reason it violates Occam's razor is because it is the strongest possible axiom you can include in a system. Why does anything happen? Because God. That's not a very interesting theory in that it can predict anything without offering any reasons or insights.

Not to mention, we have no direct observational evidence of such an entity.

Re: The universe is expanding faster than expected

#180

Post by dheera »

systemvoltage wrote: post #178
dheera wrote: post #147

Earlier quoted context omitted.

The biggest "concern" I have about the expanding universe is that although I have a lot of hope for interstellar travel at some point in the coming few millenia, intergalactic travel poses a whole another set of impossibilities to face, that I'm worried it will never be possible. The space between galaxies is pretty devoid of anything you can use as fuel, repair materials, or anything else. That space is expanding, a…

500 years from now - a shockingly small slice of time in the history of human evolution, our understanding of the universe has changed a lot. Folks, if you’re reading this from the future - we are currently mostly clueless but have made some solid progress. GIFs load 10x faster than they did just 10 years ago! This virus thing has been a real pain in the ass though.

I really wish people would stop using GIFs for video. Use at least H.264 for those cat videos -- 24-bit color and much better compression than GIF.
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