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Um… this is a hard one! Let’s think about this. Usually, when we see something expanding, such as a balloon or a baking muffin, it is expanding into the space surrounding it. It has somewhere to go as it gets larger. But the universe is everything that exists, so how can it expand? Well, it doesn’t help our floundering brains that these balloon and muffin analogies are simply inadequate.
Remember, the universe is everything. It cannot expand into anything else. At least that’s my working assumption.
First, we need to understand the bizarre concept of infinity. An infinite amount of something means there is no end to whatever that something is. You cannot count to infinity because it is theoretically impossible. There is no end.
Let’s consider the expansion of infinity. If you have a number line that goes all the way to infinity, it goes on forever, right? Now, imagine that you stretch that number line out so that there is more space between each number. If you do that, you haven’t created more numbers—it’s already infinite numbers. Instead, you’ve simply expanded the number line. There were infinite numbers before you expanded it, and there are still infinite numbers after you expanded it. Well, space itself is infinitely big before and after expansion, but now there is more space between the numbers. The same concept applies if the numbers (points in space) are not in a straight line but are scattered in three-dimensional space. Like a bunch of raisins in a muffin that is expanding as it cooks.
Wait… how do we even know the universe is expanding? Because, when we look at all the other galaxies, we can see they are all moving away from us. This can only happen if the universe is expanding.
However (this is where things get really bizarre), we have repeatedly confirmed by observation that the farther away the galaxies are, the faster they appear to be moving away from us. Huh? Yes, and the data is astoundingly consistent. The only way to explain this observation is that the galaxies themselves are not moving—but the space between them is expanding.
Is that possible? It is if you realize that space can be dynamic, not just static. In other words, space can change. Einstein’s general theory of relativity allows for space, on a very large scale, to expand or contract. The space of our universe happens to be expanding now. But remember, it is the space that is expanding, and the solid objects (galaxies) are not actually moving through that space, they are moving with that space as the space expands. Again, consider the raisins in an expanding muffin. The raisins are not moving through the substance of the muffin, they are moving with the substance of the muffin as that substance expands.
Of course, you have to remember that the “observable universe” includes only what we can see—limited to things that emit or reflect light that has had time to travel to us. So, we don’t truly know if the universe is finite or infinite. But the idea of the expanding space of the universe still holds true.
Okay, as a non-physicist, that’s the best I can do with this question. Now I have a headache.
Photo Credits:
- Expanding universe - DepositPhotos