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Webb captures iconic Horsehead Nebula in unprecedented detail

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Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#121

Post by causal »

nilkn wrote: post #113
sandworm101 wrote: post #91

Earlier quoted context omitted.

Well, no. The density in the observed universe is used to extrapolate the number of galaxies in the non-observed universe. The size of that universe is extrapolated from the rate of expansion and the time since the big bang. The size and shape of the observable universe also changes. A moving observer, say someone doing 30% of lightspeed, will see further in one direction than another. Accelerate quickly enough and t…

You’re assuming that space was compressed into a single point at the Big Bang. However, this is not implied by the Big Bang or cosmology. All we can truly infer is that the universe was very hot and dense and that spacetime experienced rapid expansion. We do not know the size, extent, or shape of space at that time, and we don’t even know how much matter and energy were present. We only have a notion of the density.

Yeah this is a difficult concept, and I think the way the big bang is commonly portrayed in media often leads to this misconception of the big bang as starting at a point in space rather than a density.

I uncovered this for myself when asking, "where is that point now?" and discovering it was never a point at all, space is expanding from all points simultaneously.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#122

Post by sandworm101 »

nilkn wrote: post #113
sandworm101 wrote: post #91

Earlier quoted context omitted.

Well, no. The density in the observed universe is used to extrapolate the number of galaxies in the non-observed universe. The size of that universe is extrapolated from the rate of expansion and the time since the big bang. The size and shape of the observable universe also changes. A moving observer, say someone doing 30% of lightspeed, will see further in one direction than another. Accelerate quickly enough and t…

You’re assuming that space was compressed into a single point at the Big Bang. However, this is not implied by the Big Bang or cosmology. All we can truly infer is that the universe was very hot and dense and that spacetime experienced rapid expansion. We do not know the size, extent, or shape of space at that time, and we don’t even know how much matter and energy were present. We only have a notion of the density.

We may not know the exact size at the start, but we know it was infinitesimally smaller than it is today. So the size of the initial universe isn't a big factor in the equations about how big it likely is today. Weather it started as a few centimeters across or a few thousand light years across, both are functionally zero compared to the current size.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#123

Post by layer8 »

rpigab wrote: post #115
layer8 wrote: post #103

Earlier quoted context omitted.

We are lucky that we live in a sweet-spot era where the universe is old enough that we have 13 billion years to look back on, but young enough that all the galaxies haven’t receded behind the cosmic horizon yet due to the accelerated expansion of the universe. In some billion years, intelligent beings will only have historic records, if anything at all, to look back to how the observable universe used to be filled wi…

What if the only place where intelligent life was ever possible in the universe is being actively made impossible to live in by intelligent beings, which means after they're gone extinct, there'll be no intelligent beings to appreciate its beauty?

That seems a quite likely outcome to me. On the positive side, once it happens, there will be no one who would mourn it.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#124

Post by nyokodo »

the_af wrote: post #53
mr_mitm wrote: post #32

Earlier quoted context omitted.

Statistics is a very precise science. Can you show your work or is it just a gut feeling?

> Statistics is a very precise science. Can you show your work or is it just a gut feeling? In my case, my gut feeling, but is it so unlikely? As mentioned in "Cosmos: Possible Worlds", planets may go through a "habitable zone", which is the window in which they are just the right distance from just the right star, and they have the right elements in their surface or whatnot. And then just the right random events hav…

> it cannot be that nowhere else but here on Earth did this happen. > I don't know if this is statistics. It surely is gut feeling.

It's possible that life emerging is so unlikely that it has never happened before anywhere even if it could happen again. We do not have the data to establish how likely and in fact we don't even have enough data to fill in all the gaps of how life on earth emerged in the first place. Our gut feelings are likely heavily influenced by science fiction or other priors and can't be trusted for knowledge but we are as a species very good at deluding ourselves into thinking we know things that we don't.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#125

Post by pdonis »

sandworm101 wrote: post #91
causal wrote: post #82

Earlier quoted context omitted.

Replying to the other replies here - this regards the observable universe. Speed of light limits and all that. Of course we have no reason to believe the universe just stops at the point where we happen to lack the ability to observe.

Well, no. The density in the observed universe is used to extrapolate the number of galaxies in the non-observed universe. The size of that universe is extrapolated from the rate of expansion and the time since the big bang. The size and shape of the observable universe also changes. A moving observer, say someone doing 30% of lightspeed, will see further in one direction than another. Accelerate quickly enough and t…

> The density in the observed universe is used to extrapolate the number of galaxies in the non-observed universe.

As has already been pointed out, our best current model of our universe is that it is spatially infinite. That means an infinite number of galaxies.

The finite galaxy numbers that astronomers give are for the observable universe.

> The size and shape of the observable universe also changes.

Not the way you are describing, no. The observable universe does increase in size as time goes on, because there is more time for light to travel so the light we see can come from objects further distant. Its shape, however, does not change.

A good reference is Davis & Lineweaver's 2003 paper:

https://arxiv.org/abs/astro-ph/0310808

> A moving observer, say someone doing 30% of lightspeed, will see further in one direction than another.

I don't know where you're getting this from. What part of the universe you can observe from a given point does not depend on your state of motion.

> Accelerate quickly enough and the "dark" side of your custom observable universe might catch up with you, causing all sorts of havoc.

This is nonsense. The Unruh effect is (a) nothing like what you are describing, and (b) irrelevant to this discussion anyway, since the Unruh effect only applies to objects which have nonzero proper acceleration, which is not the case for any galaxies, stars, or planets in the universe.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#126

Post by pdonis »

an-honest-moose wrote: post #108
layer8 wrote: post #100

Earlier quoted context omitted.

As far as we know, the total universe may have infinite size, and thus contain infinitely many galaxies.

That doesn't necessarily follow - the universe can be infinite in size, but contain a finite amount of matter.

Not the universe we observe, no. There is no valid model in GR that has this property and matches our observations of the universe as a whole. Models with a finite amount of matter surrounded by an infinite region of vacuum exist in GR, but they are not homogeneous and isotropic on large scales, while our observations indicate that our universe is.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#127

Post by layer8 »

deanCommie wrote: post #114
layer8 wrote: post #103

Earlier quoted context omitted.

We are lucky that we live in a sweet-spot era where the universe is old enough that we have 13 billion years to look back on, but young enough that all the galaxies haven’t receded behind the cosmic horizon yet due to the accelerated expansion of the universe. In some billion years, intelligent beings will only have historic records, if anything at all, to look back to how the observable universe used to be filled wi…

I don't understand people that aren't filled with dread with this concept. And I understand why so many humans fall back to something like religion to cope. It's the only way it seems to become complacent with our role in the cosmic horror. I know all the intellectual arguments for optimistic nihilism. I vote in elections even though my "one vote" doesn't matter amongst millions, and in some degree my single human li…

The change is too slow for anyone to be personally affected by it. Besides, the universe as such is devoid of any meaning; meaning is only something that we create internally. The fact that we dread voids and emptiness is also a result of evolutionary needs, there is no “dread” outside of us.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#129

Post by pdonis »

worldsayshi wrote: post #80
sandworm101 wrote: post #71

Earlier quoted context omitted.

Yes. Take the age of the universe, multiple by the rate of expansion to get the total size of the universe, then multiple by the average density of galaxies in the observable universe. There are some further complications, but at the root it is basic algebra.

Is that really the way to see it? As I understand it, the Big Bang didn't happen in "one place". The Universe is expanding from an compressed state - the Big Bang state. But there is no center point. We can only see that there's expansion but it's not from a single point. The only known "center point" is us. And the only reason it's a center point is because we can only see as far away as light has traveled since the…

> As I understand it, the Big Bang didn't happen in "one place"...there is no center point.

That is correct. The only tenable answer to "where did the Big Bang take place" is "everywhere".

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#130

Post by PeterCorless »

magnat wrote: post #118

JWST optics makes quite unique diffraction spikes. Not only that there are eight of them, but on full resolution images [1] they have distinct pattern, as if made from separate dashed lines. Are colors of those tiny lines (mostly red here - although this is false-color image) also diffraction artifacts, or do they correspond to actual spectrum of the stars causing them? [1] https://www.esa.int/var/esa/storage/images/…

That's how you can immediately tell a JWST image from Hubble; hubble has 4-spike patterns.
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