Far out cosmology: from little to big (Introduction)

by David Turell , Saturday, July 22, 2023, 19:19 (280 days ago) @ David Turell

Our expanding universe:

https://bigthink.com/starts-with-a-bang/space-big-place/?utm_campaign=swab&utm_sour...

"There are few things we can conceive of that are as mind-bogglingly large as space is. Our observable Universe, out to the deepest recesses of space that we can possibly see, takes us out some 46 billion light-years in all directions. From the Big Bang until now, our Universe has expanded while gravitating at the same time, giving rise to stars and galaxies spread across the expanse of outer space. All told, there are currently several trillion galaxies present within it, as for every galaxy we know about, there are perhaps 30 to 100 that are too small, faint, and distant for us to presently observe.

"And yet, if we go back in time, we learn that not only was our Universe a much smaller place, but that in the earliest stages, the Universe itself was anything but impressive. If the Universe has been expanding and cooling for 13.8 billion years, then long ago, it must have been smaller and denser, implying that there may not always have been such a remarkably large volume to contain all the particles that have existed for so long. Space may not always have been a big place, and it’s only the fact that our Universe has expanded so thoroughly and relentlessly that made it so big and empty today.

***

"if we went back to a time when a mere one second had passed since the Big Bang, back when the last of the early Universe’s antimatter (in the form of positrons) was annihilating away, the entire observable Universe would only be about 100 light-years in diameter.

"And it means that in the very early stages of the Universe, back when only perhaps a picosecond (10-12 seconds) had passed since the Big Bang, the entire observable Universe could fit inside a sphere no bigger than the size of Earth’s orbit around the Sun. The entire observable Universe, back in the Big Bang’s early stages, was smaller than the size of our Solar System.

"You might think that you could take the Universe all the way back to a singularity: to a point of infinite temperature and density, where all its mass and energy concentrated into a singularity. But we know that’s not an accurate description of our Universe. Instead, a period of cosmic inflation must have preceded and set up the Big Bang.

"From evidence in today’s Cosmic Microwave Background, we can conclude there must have been a maximum temperature that the Universe reached during the hot Big Bang: no more than about ~1029 K. Although that number is enormous, it’s not only finite, it’s well below the Planck scale. When you work out the mathematics, you find a minimum diameter for the Universe at the start of the hot Big Bang: around 1 meter (3.3 feet), or around the size of a human child.

***

"It’s also true that we don’t know how long inflation endured for or what, if anything, came before it. But we do know that when the hot Big Bang began, all the matter and energy that we see in our visible Universe today, all the stuff that extends for 46.1 billion light-years in all directions, must have been concentrated into a volume of around the size of a soccer ball.

"For at least a short period of time, the vast expanse of space that we look out and observe today was anything but big. All the matter making up entire massive galaxies would have fit into a region of space smaller than a pencil eraser. And yet, through 13.8 billion years of expansion, cooling, and gravitation, we arrive at the vast Universe we occupy a tiny corner of today. Space may be the biggest thing we know of, but the size of our observable Universe is a recent achievement. Space wasn’t always so big, and the evidence is written on the face of the Universe: where all of us can see the evidence."

Comment: readers here know this story. What it tells us is that as life was evolved, so was the universe evolved. This tells us God prefers to evolve His creations for His own reasons. We have no idea why He wanted it to expand to such a big size, but I'm sure God had his unknown reasons.