Far out cosmology: an edge to the universe (Introduction)

by David Turell , Saturday, April 01, 2023, 17:26 (391 days ago) @ David Turell

The telescopes we have see back just so far:

https://bigthink.com/starts-with-a-bang/edge-of-the-universe/?utm_campaign=swab&utm...

"Despite everything we’ve learned about our Universe, there are many existential questions that remain unanswered. We don’t know if our Universe is finite or infinite in extent; we only know that its physical size must be greater than the portion we can observe. We don’t know whether our Universe encompasses all that exists. And we remain ignorant about what happened in the earliest stages of all: in the first tiny fraction-of-a-second of the hot Big Bang, as we lack the necessary evidence to draw a robust conclusion.

"But one thing we are certain about is that the Universe has an edge: not in space, but in time. Because the hot Big Bang occurred at a known, finite time in the past — 13.8 billion years ago, with an uncertainty of less than 1% — there’s an “edge” to how far away we can see. Even at the speed of light, the ultimate cosmic speed limit, there’s a fundamental limit to how far back we can see. The farther away we look, the farther back in time we’re able to see. Here’s what we see as we approach the edge of the Universe.

***

"But as we look farther and farther away, we start to see how the Universe grew up to become this way. As we look to greater distances, we find that the Universe is slightly less clumpy and slightly more uniform, particularly on larger scales. We see that galaxies are lower in mass and less evolved; there are more spirals and fewer elliptical galaxies. On average, there are greater proportions of bluer stars, and the star formation rate was higher in the past. There’s less space between galaxies, on average, but the overall masses of groups and clusters is smaller at earlier times.

***

"We take for granted, today, that space is transparent to visible light, but that’s only true because it isn’t full of light-blocking material, like dust or neutral gas. But at early times, before enough stars had formed, the Universe was full of neutral gas, and hadn’t become fully ionized by the ultraviolet radiation from these stars. As a result, a lot of the light we see is obscured by these neutral atoms, and it’s only once enough stars have formed that the Universe becomes fully reionized.

"This is, in part, why infrared telescopes, such as NASA’s newest flagship mission, the JWST, are so crucial to investigating the early Universe: there’s an “edge” to where we can see in the wavelengths we’re familiar with.

***

"JWST has now taken us even farther, showing us galaxies as far back as 330 million years after the Big Bang, where they still appear large, evolved, and are not quite “pristine” in terms of the elements that are present within them. There must still be stars and galaxies out there beyond even what JWST has shown us so far.

"Beyond those limits of what our current telescopes can see, however, we can still measure the indirect signs that stars have formed: through the emission of light from hydrogen atoms themselves, which only occurs when stars form, ionization occurs, and then the free electrons recombine with the ionized nuclei, emitting light in the aftermath of that.

***

"The very first stars of all, in the rare regions that grow in mass density the fastest, are expected to come about between 38 and 40 billion light-years away, corresponding to times just 50-to-100 million years after the Big Bang.

"Before that, the Universe was only dark, full of neutral atoms, and radiation from the Big Bang’s leftover glow.

***

"And before that, 46 billion light-years away, we come to the earliest stages of all: the ultra-energetic state of the hot Big Bang, where the first atomic nuclei, protons and neutrons, and even the first stable forms of matter were created. At these stages, everything can only be described as cosmic “primordial soup,” where every particle and antiparticle in existence can be created from pure energy.

"What lies beyond the frontier of this high-energy soup, however, remains a mystery. We have no direct evidence for what occurred in those earliest stages, although many of the predictions of cosmic inflation have been indirectly confirmed. The edge of the Universe, as it appears to us, is unique to our perspective; we can see back 13.8 billion years in time in all directions, a situation that depends on the spacetime location of the observer who’s looking at it.

"The Universe has many edges: the edge of transparency, the edge of stars and galaxies, the edge of neutral atoms, and the edge of our cosmic horizon from the Big Bang itself. We can look as far away as our telescopes can take us, but there will always be a fundamental limit. Even if space itself is infinite, the amount of time that’s passed since the hot Big Bang is not. No matter how long we wait, there will always be an “edge” that we’ll never be able to see past."

Comment: We cannot see the current edge, not enough light-years of time, so Siegel has looked back to our beginning. He shows how the universe evolved. More evidence God evolves His goals.