Our Universe — Part 1
Original post date: November 22, 2018
If you are a regular reader of this blog, you will know that I have a particular interest in space science. Many previous posts have touched on entities that play a major role in our universe: time, gravity, atoms. Today I want to talk about something broader, more general, and more debatable: the universe itself. What is it made of? How old is it? Does it have a beginning? When will it end? How big is it? Most people feel they know the answers. But science is mysterious, and so is our universe.
Let's start with how the universe was born. You are likely familiar with the Big Bang theory. It is widely accepted, but it has several loopholes. While we assume the universe began with the Big Bang, what actually happened remains unknown.
The Big Bang is a theory built on present-day observations of distant stars and galaxies moving relative to our own. Edwin Hubble discovered that galaxies, stars, and everything else in the universe is moving away from us at an accelerating rate. He determined this through the Doppler effect. When two objects emitting waves move relative to one another, the frequency of the wave shifts for the observer. This is familiar through sound. With light, the same effect appears as a change in colour. An object moving away from us shifts toward red as its wavelength stretches longer. Every cosmic body observed from Earth shows this red-shift, meaning everything is moving away from us.
The connection to the Big Bang is straightforward: rewind. If everything is moving away from everything else, it must all have originated from a single point. An infinitely dense particle that began expanding and gave rise to our universe.
This seems well explained. It is not, entirely. Questions immediately follow. What surrounded that infinitely dense point? What caused it to expand? Where did it come from? The Big Bang explains the expansion, but not the origin of the origin.
The age of the universe is also derived from this theory: approximately 13.77 billion years, give or take 59 million years. This is calculated by measuring the distances and radial velocities of other galaxies, most of which are moving away at speeds proportional to their distance. Using the current expansion rate, we can rewind to the point where everything was contained in a singularity and estimate how long ago that was.
But the Big Bang is not the only theory. Quantum gravity and string theory suggest a universe that may look nothing like what human observers perceive. It could be a flat hologram projected onto the surface of a sphere. It could be a digital simulation running inside a vast computer. The Matrix is not entirely without precedent as a thought experiment.
Whatever its origin, the expansion of the universe is real. The rate is not constant, though. It increases by 67 kilometres per second per million parsecs. One parsec is approximately 3.086 × 1013 kilometres. An object one million parsecs away is gaining 67 kilometres per second in velocity every single second. That is the scale of expansion.
Galaxies and stars are not simply accelerating through space on their own. The universe is expanding, and they are carried along with it. A useful analogy is raisin bread dough. As the dough rises, the raisins do not move through the dough independently. They are carried apart by the dough itself expanding around them. The universe works similarly, on a vastly larger scale.
The Big Bang may not be the complete picture, but it is widely accepted because it answers more questions than any other theory currently does. That should not limit thinking, though. Theories like this are the biggest invitations to imagination. Who knows what the actual past looks like?
This post has covered the birth, expansion, and age of the universe. There is far more to explore: the constituents of the universe, its timeline, and how it might end. That is coming in Part 2.
Originally posted on thedopplerdude.blogspot.com.