A graphical representation of the expansion of the universe
from the Big Bang to the present day, with the inflationary epoch
represented as the dramatic expansion of the metric seen on the left.
This visualization can be confusing because it appears as if
the universe is expanding into a pre-existing empty space over time.
Instead, the expansion created, and continues to create,
all of known space and time.
(Wikipedia)
Copyright © 2020
by Ralph F. Couey
Written content below only
I've been holding off on this post because I wanted to be able to explain the complexities of the science involved without losing you or confusing me.
As I said before, I've been a steady customer of the Science Channel's excellent program "How the Universe Works." I've learned a ton, made easier by the eminent skill of the PhD presenters to make it simple enough to understand.
About a month ago, there was an episode that dealt with the expansion of the universe. Basically, since the Big Bang, everything has been expanding outward to form what we know as the observable universe. Here's the first big idea. I always thought that what was expanding was the component parts (galaxies, etc) expanding into pre-existing space. Actually what is happening (see the image at the top of this post) is that space itself is expanding. Outside the borders of the known universe, nothing -- nothing exists. Not stars, not dust, not even space itself. Mind blown.
Back in the late 1920's, A former mule team driver, Milton Humason, was working at the Mount Wilson observatory above, as Dr. Sagan put it, what was then the smog-free skies of Los Angeles. He had been taking spectrograph images of distant galaxies. Now, a spectrograph is a handy tool for determining the chemical makeup of distant objects by taking that light and focusing it through a prism. The prism then breaks the light down into its component parts, identifying things like oxygen, calcium, and other elements, all which have distinct frequencies in light. But Humason discovered something more astonishing. The telltale bands that identified those chemicals was shifted towards the red end of the spectrum.
This is an exercise of the Doppler effect. Objects that are receding from the observer produces light waves that are stretched out, while objects coming towards the observer will be squished closer together. To understand this, one simply needs to stand near a freeway and listen to the sound of, say, a truck as it passes you. The sound of the engine will drop down in pitch. Same thing, as sound and light at least in this case act the same. An astronomical object shifted towards the red end of the EM spectrum means that it is speeding away from us. The thing is, the more Humason, and others later on, probed the universe, it was proven that the everything out there is speeding away from us. And what's even more astonishing is that the speed of that expansion is increasing.
For a long time, there have been three major theories about the fate of the universe. One is called the Big Crunch, which hypothesized that the universe would expand out to a certain point, then begin to contract, all the way down to the singularity that existed in the milliseconds before the Big Bang. This theory supposed that the universe would undergo cycles of expansion and contraction pretty much forever.
Another theory can be called the Big Chill. In this case, the universe expands until the stars all die out, and all the cold gas and dust which is the raw materials for star birth, would be used up. Space would become dark and cold, populated only by the cold cores of dead stars.
The third main theory is called the Big Rip. This one is a little harder to understand, but in this case, the universe continues to accelerate its expansion until the very fabric of spacetime (stay with me here) along with all its component atoms and molecules are simply torn apart.
These theories were debated endlessly, but recent work has produced the evidence favoring the Big Chill. The important part of this understanding involves two relatively new ideas, dark matter and dark energy.
Dark matter as a term is simply a place-holder scientists use to understand a basic idea about mass and gravity. In recent years, the mass of the entire known galaxy has been estimated. The thing is, in the way we understand gravity (which is produced by mass) there simply isn't enough mass to account for the amount of gravity that keeps things together. Solar systems and galaxies should not be out there in their placid spirals, but instead should be flying apart. Scientists decided that the missing mass was something that was so far invisible to any of our feeble detection instruments. Hence, the term Dark Matter. Invisible or not, it had to exist because the universe could not exist without it.
Dark energy, another place-holding term, is kind of the same idea. The accelerating expansion of the universe is being driven by some kind of energy, again undetectable to human science. Hence the term Dark Energy.
Now, the balance between these two forces keeps the universe in the form we see it today. But if dark matter dominates, the universe, pulled by that gravity, will collapse on itself. On the other hand, if dark energy wins, the universe flies apart.
There are some strange things out there that defy explanation. For example, the universe is about 13.5 billion years old. Because of the speed of light, we should be able to only detect objects 13.5 billion light years away, as it would take that long for light from those distant objects to hit earth's telescopes. Now the universe is estimated to be about 93 billion light years in size, but we can only see as far out as light has had time to reach us. In theory, if we had a telescope powerful enough, you could look all the way back to the Big Bang.
But recently, astronomers imaged a very early galaxy. It wasn't a pretty spiral like the Milky Way or Andromeda, it was just...well...a blob. Kinda looked like an amoeba. The startling thing is that the object was found to be 38 billion light years away. The only way for that to be possible is for that galaxy and us to be receding from each other at a rate greater than the speed of light. Einstein's Theory of Relativity states that no material object can be accelerated beyond light speed, mainly because there's no energy source able to propel it that fast. So, this has perplexed scientists and as far as I've heard (and on this subject I'm far from an unimpeachable source) there hasn't been a satisfactory idea that explains this. At some point, that will be figured out. I never put anything beyond a determined scientist.
As I've written before, I spend time outside staring up at the universe, thinking really big thoughts. After watching and re-watching the three or four episodes covering these concepts, my mind was completely blown. It was one of those moments when I realized just how massive the universe is, and just how tiny and over-matched is my brain.
Now, the time frame for these events is in the trillions of years. Long before the end comes, whichever form it takes, not only will humans be gone, but our planet, our solar system, and our sun will have become just dust and gas, perhaps used to form a few new stars. So I don't worry about The End. Instead, I remain amazed and astonished at just how unimaginably huge and complex is this whole thing we call the universe. And just how far we have to go before understanding even a tiny piece of it.
For now, I will continue to look up and just be amazed.
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