Spacetime – Our Expanding Universe

The first thing we truly learn about time, is that it is a purely relative concept. A thousand years, to us, may seem like ages, but in the lives of rock and sand, is but a minuscule measurement of time. The Sun you see in the sky is actually what it looked like approximately eight minutes ago. The sheer size of our Universe prevents us from establishing a Universal time according to which all things take place.

A common idea in most writings is that the expansion of the universe and Time itself, are co-related. As the Universe expands, Time progresses. Some theories speculate that Dark energy causes our Universe to expand at accelerating rates. However, some theories predict that the Universe is expanding at ever-decreasing speeds, due to the constant pull of gravity. This would imply that the progress of time has also begun to slow. And what happens when the Universe stops expanding?

When the pull of gravity eventually halts the expansion of our Universe, according to the theory above, Time would stop. Of course, it wouldn’t stop there. Gravity would then reverse the growth of the Universe, causing it to collapse, the very same way it expanded after the Big Bang, until it results in a black hole singularity. This scenario is named The Big Crunch. Time would reverse, and we would end up pretty much the same way we started. A tiny, tiny, tiny pinpoint of energy that may or may not cause a new Big Bang.

Of course, this is if we accept the scenario where the Universe is expanding at a decreasing rate. We mentioned two possible ways the Universe would expand. (A quick refresher: We can only go one of two ways. Either the Universe expands slower, because of Gravity, until it stops. Or it expands faster due to Dark Energy, which pushes the Universe apart.)

-Decreasing: The Universe cycles through phases of expansion and contraction. That is, repeating Big Bangs and Big Crunches, exactly the same every time. Since Time is being reversed, every atom will follow the same path it took to get to this point, backwards, until it reaches the stage at which it was during the Big Bang. Each cycle, the same stars would form, the same planets would rise, and the same people would live and die.

-Accelerating: The Universe continues to expand at increasing rates. Time moves faster and faster, until at one point, the energy (which, like mass, is constant) becomes uniformly spread out over the entirety of the Universe. This scenario is termed as “The Heat Death of the Universe”. A constant temperature, according to extrapolations of the second law of thermodynamics, would imply that motion or work would no longer be possible. Furthermore, this scenario would most likely lead to temperatures too low to sustain biological life.

While these are two of the more commonly accepted theories, there’s no limit to the number of theories out there. We could talk about Multiverses or parallel dimensions, but those are topics for another time. In what I have detailed here, I seek not to relay facts, but theories and opinions, and I hope to hear your ideas as well.