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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

#131

Post by pdonis »

mvkel wrote: post #104
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.

Isn't the rate of the expansion of the universe increasing? And that assumes the observable universe is homogeneous, which it isn't

> Isn't the rate of the expansion of the universe increasing?

It is now, but up until a few billion years ago, it wasn't, it was decreasing. Many of the objects we currently see are far enough away that the light we are now seeing from them was emitted while the universe's expansion was still decelerating.

> that assumes the observable universe is homogeneous, which it isn't

No, the models cosmologists use do not assume the universe is homogeneous period. They only assume it is homogeneous on average, on large distance scales (roughly scales larger than the size of the largest galaxy clusters).

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#132

Post by layer8 »

zidel wrote: post #120
layer8 wrote: post #96

I wonder what the red and blue stripe artifacts are in the lens flares.

The 6+2 spikes around the bright stars is a diffraction pattern created by the edges of the hexagonal mirror segments (the six large spikes) and the three struts that hold the secondary mirror (also six spikes, but four overlap with the mirror spikes). https://smd-cms.nasa.gov/wp-content/uploads/2023/07/webb-dif...

I’m aware of that. I was talking about the repeating pattern of blue and red stripes within the spikes.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#133

Post by nilkn »

sandworm101 wrote: post #122
nilkn wrote: post #113

Earlier quoted context omitted.

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.

We don’t know that, though. Consider an evolution of a flat coordinate plane given by (x,y) -> (e^t * x, e^t * y). This process can run forever and has the property that all points appear to move away from all other points through time, yet the size of the plane never changes.

It’s better to think of the Big Bang as describing a point in time rather than a point in space.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#134

Post by relaxing »

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/…

The color gradation is due to phasing effects from the different wavelengths of light being combined, and the checkerboard effect is an artifact of the segmented mirrors.

JWST has separate modes for spectroscopy. They’re pretty cool!

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#135

Post by sandworm101 »

causal wrote: post #121
nilkn wrote: post #113

Earlier quoted context omitted.

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.

The easy answer to the hard concept is that the big bang is not the increase in size of a thing. It is an increase in dimensions, including time. Our notions of size, of dimension, might not exist outside the bubble. We would therefore never perceive an edge, but that doesn't mean that one does not exist nor that there may be a finite size.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#136

Post by dotnet00 »

mvkel wrote: post #112
dotnet00 wrote: post #88

Earlier quoted context omitted.

The observable universe has a size, the cosmic microwave background is what we 'see' at the 'edge' in terms of photons (~400k years after the big bang). We could see further if we could map out the gravitational wave or neutrino backgrounds (1 sec after the big bang). But for now we can't really say if the universe in its entirety has a finite size.

Fascinating. Do you think it's possible that we can map these out in the next 50 years?

For the gravitational wave background, maybe with LISA we might be able to get a glimpse, but the neutrino background seems like it'd take some truly unprecedented breakthroughs in our ability to detect neutrinos to have any chance of mapping it out.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#137

Post by skilled »

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?

Buddhism is deeply rooted in reincarnation and the progression of a common person to an enlightened being through different ranks over the span of multiple lifetimes.

I am pretty sure there is a dimension of life that we have yet to discover and learn about. And for the time being Buddhism is the only “religion” that openly discusses this progression.

Hinduism has the same but in my experience it’s a lot more reserved. Bali is a great example of this (which has a strong Hinduism foundation), of how you can create “paradise on Earth” and yet 99.99% of tourist’s don’t ever encounter the root of that paradise.

Humans will learn the full extent of life long before they go extinct.

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#138

Post by nsbk »

the_af wrote: post #49
devsda wrote: post #30

That's an incredibly detailed image. Every single time I see one of these amazing space pics, it's hard not to get all philosophical and wonder about the size of space & time on cosmic scale, how small our earth is and how insignificant our regular problems are. I don't care if I don't get to see flying cars or AGI in my lifetime but I will be very disappointed if our knowledge of space remains more or less the same…

> it's hard not to get all philisophical and wonder about the size of space & time on cosmic scale Indeed! Never a bad time to re-watch Cosmos and (in my opinion) the awesome sequel(s) by Neil de Grasse Tyson. Is it weird to admit I even choke up during some of the episodes? (As an aside, why is it so hard to find the sequels to Cosmos in any streaming service. In my country it's not on Netflix, Disney+, Apple, HBO/M…

You are not alone

Re: Webb captures iconic Horsehead Nebula in unprecedented detail

#140

Post by Nevermark »

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.

The unobserved universe is likely to be many orders of magnitude larger than the observed universe. It is possible that it is unimaginably larger.

Technically, it is possible that the unobserved universe is infinite, however whether that is a credible option depends on individual scientists informed intuitions. We simply have no experimental or theoretical evidence either way at this point.

So there is no estimate of how many galaxies there are in the universe in toto.

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