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Webb and Hubble confirm Universe's expansion rate

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Re: Webb and Hubble confirm Universe's expansion rate

#281

Post by dvsfish »

mrguyorama wrote: post #270
dvsfish wrote: post #157

Earlier quoted context omitted.

While its probably totally wrong, I think your tone and general attitude to people throwing around imaginative and creative ideas is extremely unproductive and frankly rude. If you want to stifle creative discussions, this is exactly how you'd do it. I found the post to be very stimulating regardless of its validity. And it's not like they're trying to spread it as gospel. There was a lot of disclaimer.

If you want creativity, take an art class. This is cosmology, ostensibly a science. Pulling wild ideas out of thin air and basically ad-libbing a "theory" is not.

So we have to put everyone who dares to imagine down about it? I see value in sharing a wild idea purely for the inspiration it may give others to think about things from a unique perspective. A lot of great science started as a strange idea.

Re: Webb and Hubble confirm Universe's expansion rate

#282

Post by sebzim4500 »

theoreticalmal wrote: post #141
throwawaymaths wrote: post #85

Earlier quoted context omitted.

There's a 'fringe' theory that the CMB is not the echo of the big bang but rather the redshifted black body radiation of intergalactic dust (apparently the numbers are about right). Although the primary proponent of this theory is trying to justify some sort of cyclic universe model with it, if my understanding is correct it would still be compatible with a 'standard' big bang that has the "longer" (aka galactic expa…

I can’t believe it. First they take Pluto from us, next they’re going to tell me the static on my tv set isn’t the remnants of the Big Bang, but just hot dust? My childhood is crumbling!

The static on your TV set is <1% CMB, mostly it is interference from other man-made sources and IIRC there is some coming from the sun.

Re: Webb and Hubble confirm Universe's expansion rate

#283

Post by pdonis »

lp4vn wrote: post #150
pdonis wrote: post #113

Earlier quoted context omitted.

> I'm picturing more of an explosion in empty space. No, that's not what the big bang is. > this would imply a "center" to the explosion, which I've also heard is not the case That's correct. The big bang does not work like anything ordinary that you are used to imagining. The math is straightforward and unambiguous, but there is no good ordinary language description that corresponds to the math.

As I understand it, before the big bang the whole observable universe was contained in a small sphere and then it started to expand metrically. Is this interpretation correct? Another thing: suppose I point a laser beam to the space and by chance this laser beam never finds any kind of matter in its way, where is this laser going to? To an infinite void? Is it correct to say that stars radiate energy to the infinite…

> before the big bang the whole observable universe was contained in a small sphere and then it started to expand

We have no evidence of any time when the universe was not expanding. At the earliest times we have evidence of, the universe was already expanding (extremely rapidly--much, much, much more rapidly than it is now). At those times, our observable universe was indeed contained in a very small volume.

> suppose I point a laser beam to the space and by chance this laser beam never finds any kind of matter in its way, where is this laser going to?

Since the universe is spatially infinite in our best current model, the laser beam will just keep on going forever.

> To an infinite void?

According to our best current model, no, the laser beam will never stop passing by matter, of approximately the same average density as the matter we can see.

> Is it correct to say that stars radiate energy to the infinite then?

Yes, as long as you recognize that "the infinite" never becomes a "void".

Re: Webb and Hubble confirm Universe's expansion rate

#284

Post by baq »

explaininjs wrote: post #276
mrguyorama wrote: post #273

Earlier quoted context omitted.

>or we need the existing models to propose a way it was initialized. We have that, it's the big bang.

How remarkably unsatisfactory. The argument being: You can't propose physics ever changed, that'd mean energy could have been created at some point! Energy was created at some point, wouldn't it be nice to know when? Everything created at the Big Bang exactly as it is now, stop asking questions.

Nobody argues it wouldn't be nice. Physics argues we can't ever know. It's a rather significant difference and if this gets proven wrong, you'll find that physicists are the ones partying the hardest.

Re: Webb and Hubble confirm Universe's expansion rate

#285

Post by pdonis »

pigpang wrote: post #207
lp4vn wrote: post #150

Earlier quoted context omitted.

As I understand it, before the big bang the whole observable universe was contained in a small sphere and then it started to expand metrically. Is this interpretation correct? Another thing: suppose I point a laser beam to the space and by chance this laser beam never finds any kind of matter in its way, where is this laser going to? To an infinite void? Is it correct to say that stars radiate energy to the infinite…

It's just an interpretation. Your interpretation is similar to the Big Bang model of visible Universe expansion. If you can convince us that your model is better than other models, then we will use your model, but nobody can prove than a model is correct, unless we will find a hidden recorder somewhere which was turned on for few dozens of billion years. Photon will hit something, or will travel until it will be reds…

> It's just an interpretation

No, it's not, it's our best current model's description of the actual physical reality of our universe.

> nobody can prove than a model is correct

That's true, but it's also true that we can show models to be incorrect, as in, falsified by the data. For example:

> Photon will hit something, or will travel until it will be redshifted to obvilion, or will travel until end of the medium

For the scenario that was posed, a laser beam that never hits anything, none of your statements here are true. The first is ruled out by the scenario; the second is known to be false because there is no "gravitational redshift" of light in the universe as a whole (because models in which there would be such a redshift are known not to correctly model our data on the universe as a whole), and there is no "end of the medium" (again, models in which there would be an "end of the medium", i.e., where the universe stopped containing matter and started being just vacuum, are known not to correctly model our data).

I have described what actually happens in my own response to the GP upthread.

> (photon is a wave, so it waves something).

Light is an electromagnetic wave; what "waves" is the electromagnetic field. (If you use a "photon" model, you are using the quantum electromagnetic field as opposed to its classical approximation.) There doesn't have to be any other "medium"; the electromagnetic field is present everywhere.

Re: Webb and Hubble confirm Universe's expansion rate

#286

Post by pdonis »

1d22a wrote: post #161
pdonis wrote: post #118

Earlier quoted context omitted.

Meaning, why did the expansion change from decelerating to accelerating a few billion years ago? Because that was when the density of matter, which had dominated the dynamics until then, became smaller than the density of dark energy, which has dominated the dynamics since then. The dark energy density doe not change with time, but the density of matter decreases as the universe expands.

How is is that dark energy density does not change with time? Surely the total amount of dark energy has to be constant (energy can't be created or destroyed, and all that), and then as the universe expands, that's then the same amount of energy over a larger volume, right?

> How is is that dark energy density does not change with time?

Because that's how a cosmological constant works.

There are alternate models where there is "dark energy" (as in, stress-energy that causes accelerated expansion) whose density does change with time (for example, a "Big Rip" model in which the dark energy density increases with time), but such models do not match our best current data.

Re: Webb and Hubble confirm Universe's expansion rate

#287

Post by nsxwolf »

dexterdog wrote: post #241
whimsicalism wrote: post #235

Earlier quoted context omitted.

yeah i would call estimating it as 20x when it is actually 400x firmly within “not having a clue”. He didn’t say nobody had a clue about heliocentrism.

But I believe he was the winner for many years under price is right rules.

Smugly: "1 mile."

Re: Webb and Hubble confirm Universe's expansion rate

#288

Post by orra »

explaininjs wrote: post #276
mrguyorama wrote: post #273

Earlier quoted context omitted.

>or we need the existing models to propose a way it was initialized. We have that, it's the big bang.

How remarkably unsatisfactory. The argument being: You can't propose physics ever changed, that'd mean energy could have been created at some point! Energy was created at some point, wouldn't it be nice to know when? Everything created at the Big Bang exactly as it is now, stop asking questions.

You're asking to go too far back in time.

The difficulty is we don't know what happened in the first planck second after the big bang, let alone before the big bang (if that's meaningful).

We haven't unified quantum mechanics and relativity. Hence we can't be certain that singularities exist, or that the universe started off in a singularity.

Re: Webb and Hubble confirm Universe's expansion rate

#289

Post by swamp40 »

I cannot for the life of me understand how you look at the cosmic background radiation - which appears equally in every direction you look, for as far away as you can see - and say this is evidence of a "big bang", originating from a single spot at a single point in time. And the universe just "expanded faster than light" to cover everywhere with the same consistent drab layer of cosmic background radiation.

It seems like a child's fairy tale to me.

Re: Webb and Hubble confirm Universe's expansion rate

#290

Post by justsid »

dexterdog wrote: post #241
whimsicalism wrote: post #235

Earlier quoted context omitted.

yeah i would call estimating it as 20x when it is actually 400x firmly within “not having a clue”. He didn’t say nobody had a clue about heliocentrism.

But I believe he was the winner for many years under price is right rules.

Can you claim to be a winner under the rules of a game that won’t be invented yet for hundreds of years?
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