# Are we moving through space, is the universe just expanding, or both? Does everything rotate the same way, galaxies, planets, anything? How do we know if we’re moving through space?

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Edit: Also, if we are moving through space, does everything move the same direction? (For instance all moving away from one point or towards one point)

Can you clarify if, as far as we know, was the big bang an explosion or just the focal point for all of our existence?

Are we moving through space, or is the universe just expanding so it appears we are moving through space? Like a dot on a balloon that is being blown up. It appears to be moving, but really isn’t.

And does everything rotate the same direction?

In: Physics

> For instance all moving away from one point or towards one point

This is the main thing right here. There is no one point that everything is moving relative to or positioned relative to. It’s a fundamental property in physics, that there is no one correct reference point, which makes the question “are things, in general, moving?” meaningless. To make it a meaningful question, you have to change it instead to, “is this thing moving relative to that thing?”

Example: Two cars driving opposite directions pass each other on the highway. Their speedometers both read 60mph. If you choose a person standing next to the road as a reference point, both cars are going 60 mph (or one is 60mph and the other is -60mph if you’re keeping track of directions). If the driver of one of the cars is the reference point, then the other car is going 120mph.

>Can you clarify if, as far as we know, was the big bang an explosion or just the focal point for all of our existence?

The big bang was the expansion of space itself, which carried matter outward as it expanded. It wasn’t so much an explosion of matter, but of space.

>Are we moving through space, or is the universe just expanding so it appears we are moving through space? Like a dot on a balloon that is being blown up. It appears to be moving, but really isn’t.

The expansion of the universe is like dots on a balloon. Objects do however move within space also, so the dots on the balloon are spreading out as the balloon inflates, but they also move around the surface of the balloon at the same time.

>And does everything rotate the same direction?

No. Galaxies will tend to have most things in them rotate in the same direction, because they formed from giant disks of dust and whatnot. As all that dust collapsed under gravity, it keeps the spin from before, because of conservation of momentum and the collisions between all that stuff knocking things going the wrong way into going the same way as other particles in the disk. There is however a chance for individual objects to rotate opposite or at some other angle. Individual galaxies can all have different directions of rotation.

> Are we moving through space, is the universe just expanding, or both?

Both.

Earth is spinning on its axis. It is also revolving around the Sun. The Sun is revolving around the center of the Milky Way. The Milky Way is drifting through the universe and interacting with nearby galaxies through gravitation.

In addition, the universe is expanding, and by that I mean space-time itself is getting larger, as though there were “more space” pouring out of every point in the cosmos all the time. This phenomenon is pushing all the other galaxies away from us.

> Does everything rotate the same way, galaxies, planets, anything?

No. Objects within a particular system, like the planets in our solar system, generally orbit the Sun in the same direction. But the planets in a nearby star system could be orbiting the “opposite” way as us, and star systems and galaxies aren’t lined up on the same planet as each other (some are tilted so it’s like we’re looking “down” on them, etc.). Venus spins on its axis the opposite way as Earth, but still orbits in the same direction.

> How do we know if we’re moving through space?

Every day the stars move a little bit compared to where they were yesterday. This demonstrates that we’re orbiting the Sun. Some stars move relative to each other over very long periods of time, showing that they, and we, are drifting through the Milky Way.

> was the big bang an explosion or just the focal point for all of our existence?

The Big Bang was a rapid expansion event out of a singularity, when all of matter and energy was condensed into a tiny point. In a way, we are still in the Big Bang because the universe continues to expand (and apparently will continue expanding forever). It wasn’t an “explosion” as we think of explosions, it was more like a balloon blowing up.

> Like a dot on a balloon that is being blown up. It appears to be moving, but really isn’t.

Yes, this is a good analogy. Another analogy that helps you think about it in three dimensions is a loaf of raisin bread in the oven. The loaf expands, carrying the raisins farther apart from each other. The raisins themselves aren’t moving by themselves, they’re just being pushed apart by the rising bread. In the case of the universe, though, galaxies do have some of their own movement because of gravity. Gravity is much stronger than the force of expansion, which is why you and I aren’t flying apart.