from Big Think

The consequences of traveling in a straight line forever

Is the Universe finite or infinite? Does it go on forever or loop back on itself? Here’s what would happen if you traveled forever.

travel straight line
In a hypertorus model of the Universe, motion in a straight line will return you to your original location, even in an uncurved (flat) spacetime. Without access to a higher-dimensional view of what our 3D world appears to be like to us, we cannot know or measure its true extent and shape in space.

The Universe is a vast, wondrous, and strange place. From our perspective within it, we can see out for some 46 billion light-years in all directions. Everywhere we look, we see a Universe filled with stars and galaxies, but are they all unique? Is it possible, perhaps, that if you look far enough in one direction and see a galaxy, that you’d also see that same galaxy, from a different perspective, in the opposite direction? Could the Universe actually loop back on itself? And if you traveled far enough in a straight line, would you eventually return to your starting point, just as if you traveled in any one direction for long enough on the surface of the Earth? Or would something stop you?

It’s a fascinating question to consider, and one that Bill Powers wants us to investigate, asking:

“Space and time are mind-boggling to me. It seems like if you traveled in a straight line, you could travel forever. What would stop you? A wall? [And if so,] what’s on the other side of the wall?”

Although it sounds nonsensical, the answer is both. You could travel forever, and also, something would stop you. The key lies in understanding the expanding Universe, which itself is one of the most mind-boggling concepts of all.

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