Lots of questions about the various dimensions of motion that we experience on Earth, based on my post featuring these cute animations. Let me see if I can tackle them all together … hold on to your hats!
Does our motion through the universe (maxing out at 800 km/s or so) determine how we experience time? In short, no. Theoretically, you’d experience the same “time” whether or not we were moving through the universe, or around the Milky Way, or around the sun. “Time”, as we think of it in the cosmological sense, is inherent to the universe, it’s the state of now being different from then, and thanks to entropy, always moving in one direction.
Time, as we have defined it, is a set of hashmarks we assign to the motions and vibrations of the universe to make it easier to mark how far past “then” we are when we say “now”. Take the second. It simply describes how long it takes a cesium-133 atom to wiggle 9,192,631,770 times. It’s just much easier to say “800 km/s” rather than “800 km/9,192,631,770 cesium-wiggles”. And since we can assume that cesium-133 atoms (and sheep) wiggle the same way everywhere in the universe…
… time, in the sense of something that just exists, is universal.
How you experience time is probably a much more local phenomenon. We don’t really experience the passing of seconds, for instance, not in the big scheme of things. But thanks to our particular orbital radius around a particular star on a particular rocky planet that itself rotates at a particular velocity, we do experience something called a “day”, which would be pretty meaningless to anything that didn’t evolve on Earth (although Earth’s “day” has changed over time, and will continue to change), whether they were from another galaxy or just the next planet over.
But as confused as those aliens would be by our “day”, they would probably be totally comfortable with the “second”, because of the aforementioned shared cesium-wiggles. You have biological processes tuned to it, too, called “circadian rhythms”. So “time” is a universal phenomenon, but our experience of it is a very terrestrial thing.
So if aliens came to Earth from a planet that rotated at a different velocity, would they feel uncomfortable? No, probably not. At least not because of the rotation thing. The fact that they were on an alien planet might throw them for a loop, though.
Do you feel yourself rushing through space as Earth rotates? I don’t. Say you’re reading this on the equator. For every second that you scan this page you travel half a kilometer (that velocity decreases the closer you get to the poles, because spheres). It helps that the atmosphere is also moving along with us, otherwise that would be a helluva breeze to overcome.
Gravity is what’s primarily responsible for how you “feel” on this planet, in a non-emotional sense, and that is what would most affect any alien visitors, in a non-emotional sense. And gravity, as we all remember from every science class ever, is an attractive force that is relative to the masses of objects interacting at a particular distance. How strong, or weak, gravity was on their home planet would depend on how massive their planet was, and they would have evolved along with that gravity, no matter if it was lighter or heavier (I happen to think evolution would be a universal trait of living systems, so there).
Maybe they’d have metal bones, because their planet had supergravity. Or maybe their home planet had less gravity, and they’d be made of gel, and they’d look like this:
Incidentally, how fast a planet spins around its axis doesn’t depend on its mass, or size. It’s the result of a very random set of banging and collision events along the formation of that planet from dust to big round thing.
However, if someone somehow instantly stopped Earth, you’d feel that. Just as you broke the sound barrier.
So what’s up with that Cosmic Microwave Background velocity? Not only is Earth rotating around its axis, and orbiting the sun, and the solar system around the galaxy, and the galaxy around the local cluster … but our galaxy is moving with respect to the Big Bang itself. Since the universe has no edge, I can understand if that’s a bit hard to wrap your head around.
The CMB is a bunch of radiation that’s been radiating since ~380,000 years after the Big Bang, when atoms began to form and stuff could actually start to fly through this new thing called “space” without banging into plasma clouds. It’s been chugging along in straight lines since then, and as the universe expands those waves have been streeeeeeeeetched out into the microwave range. like pulling on the ends of a rubber band.
Because the universe has no center, that CMB radiation should look essentially the same in every direction. Except that it doesn’t. If we look in one direction, it’s redshifted (meaning we are moving away from that direction). And in the opposite direction it is blueshifted (meaning we are moving towards that direction). You know, like the Doppler effect and how ambulance sirens sound weird as they pass?
Anyway, the shift looks like this when applied to the CMB:
Something in the sky in the direction of that blue bulge is sucking us in at a few hundred kilometers per second. This is very hard to measure, considering all the other movement that’s going on, but it’s happening. Current theories suggest it could be a set of supermassive galaxies pulling on our galaxy, but we haven’t been able to observe them. So basically we don’t know. If that last part makes your head spin, head over to Starts With A Bang and read Ethan’s excellent explainer.
So, how far have you moved since you started reading this?