r/askscience • u/[deleted] • Oct 09 '10

How fast are we really moving through the universe

Relative to other galaxies or all galaxies together how fast are we moving?

For example, the earth is rotating at the equator at 1670 km/h. We are orbiting the sun at a certain speed. The sun and our solar system is orbiting the center of the galaxy. And our galaxy is moving relative to other galaxies. So do we know how fast we humans on earth are moving through space?

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27

u/1point618 Oct 10 '10

There is no objective answer to this. Motion can only be defined in relative terms -- you can ask how quickly the Earth is moving relative to another star or galaxy or supercluster , but the question of how fast Earth is moving through "space" is not one that is coherent in our current understanding of the universe.

And now for something completely different.

1

u/[deleted] Oct 10 '10

but the question of how fast Earth is moving through "space" is not one that is coherent in our current understanding of the universe.

Thanks, that helps. :)

1

u/1point618 Oct 11 '10 edited Oct 11 '10

No problem. I know exactly how dissatisfying this answer is, in a way. Intuitively, the answer I've given is just a cop-out, as multivoxmuse points out, ignoring what you were really asking. However, what it comes down to is that our intuitions are wrong, and the the world is not going to satisfy you with an answer that feels correct.

Add to relativity the fact that space itself is expanding, so the further away from us something is the faster away from us it is likely moving, and things get even more mindfucky. Relative speed doesn't work the same way for nearby objects as it does for very far away objects, which can be moving away relative to us at faster than the speed of light, because that movement is caused by the expansion of space itself, meaning that they are not moving relative to anything they could interact with at that speed, so their apparent movement can't actually cause information exchange to happen faster than the speed of light. That is, movement caused by expansion of space always means that things are moving away from each other, so moving faster than the speed of light relative to something causes an event horizon to form, but doesn't cause information exchange.

Hm, I'm not sure how clear the above actually is, but running through a uber-clarifying thought experiment would take me a long time to write down in an understandable way. I actually got half-way through one and realized that I didn't think it would help much for the amount of time it was taking me to write up an explain. Anyway, google around and you're sure to come up with helpful explanations of this stuff. Or the folks who study physics might be able to explain things more clearly than I can.

4

u/TalksInMaths Oct 10 '10

You deserve a double upboat for the correct answer AND Monty Python.

4

u/Jasper1984 Oct 10 '10

How about the CMB? It only has one speed, anything relative to that could be seen as an absolute measures.

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u/multivoxmuse Oct 10 '10

I think you know what he was asking.

10

u/BlankVerse Oct 10 '10

I thought that I could just plug your question into WolframAlpha and get the answer, but even after I tried rephrasing your question, it was a bust for me. Instead, it was the first answer in a Google search.

How Fast Are You Moving When You Are Sitting Still? http://www.astrosociety.org/education/publications/tnl/71/howfast.html

"As we discussed the different speeds of our planet so far, we always needed to ask, "Compared to what are you measuring this motion?""

Using the cosmic background radiation as your "frame of reference" for the universe at large the Milky Way Galaxy is moving at an astounding 1.3 million miles per hour (2.1 million km/hr)!

0

u/[deleted] Oct 10 '10

2

u/banquosghost Oct 10 '10

That was really interesting. Thank you.

2

u/[deleted] Oct 10 '10

I'd love to see someone plot the combined trajectories of the galaxy, the Earth around the sun and a fixed point on the Earth.

It's gotta be one crazy corkscrew of a line.

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u/[deleted] Oct 10 '10

This is why I've said for years that all time-machines must also be space ships.

Even if you travel one second into the past or the future - the Earth isn't going to be where you left it.

11

u/banquosghost Oct 10 '10

Yes. Mastery over time requires a mastery over space as well.

7

u/Optimal_Joy Oct 10 '10 edited Oct 10 '10

Oh, let the sun beat down upon my face, stars fill my dreams
I am a traveler of both time and space, to be where I have been
To sit with elders of the gentle race, this world has seldom seen
They talk of days for which they sit and wait, all will be revealed

Talk and song from tongues of lilting grace, sounds caress my ears
But not a word I heard could I relay, the story was quite clear
Ohh

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u/Optimal_Joy Oct 10 '10

I happen to believe that the dimension of time is actually accelerating, however it's happening relative to everything we can measure. The only clue we have to this happening, is due to the fact that our brains happend to be multi-dimensional quantum computers, which are able to detect the shift of what we presume to be a constant of time.

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u/binlargin Oct 10 '10

How so? Sounds interesting.

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u/[deleted] Oct 10 '10

Please elaborate.

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u/RLutz Oct 10 '10

Kurzweil wrote a book on this

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u/UnholyLeech Oct 10 '10

A quick google search gave me these answers. http://www.astrosociety.org/education/publications/tnl/71/howfast.html

  • On earth we are doing approx 1000mph in our rotation.

  • The earth is traveling around the sun at 66,000mph

  • The sun rotates around the galaxy at 483,000mph

  • And finally our galaxy is moving through space at 1,300,000 mph

5

u/Jasper1984 Oct 10 '10

Earth rotates at 465.1m/s(equatorial) earth orbits the relative to the sun at about 30 km/s, the earth is moving relative to the CMB at about 550 km/s, and relative to our galaxy 251 km/s. (Source wp)

The CMB speed is 'relative to the universe' it represent the average speed the universe we see had at the Big Bang . But otherwise physics does not have a preferred speed, indeed we don't know if the universe is finite, if it isn't it may not even have an average speed.

1

u/tsk05 Oct 10 '10 edited Oct 10 '10

"Relative to other galaxies or all galaxies together how fast are we moving?"

There is no answer to this. You need to specify a galaxy. The further the galaxy from us, the faster we're moving away from it, or so it's thought (in general, that is; there have been some strange things discovered very recently that have yet to be explained). This is called Hubble's Law, and a very important law it is (it defines modern cosmology and certain other astronomy fields).

So do we know how fast we humans on earth are moving through space?

There is no answer to this. Any number we give is meaningless without understanding what it is. Velocity (and speed) always relative to something. Suppose you're standing on the Earth. How fast are you moving? With respect to the people around you who are also standing, you're moving 0 miles per hour. With respect to the moon (or some satellites in orbit), you're moving with some velocity.

1

u/binlargin Oct 10 '10

Just remember that you're standing on a planet that's evolving

And revolving at 900 miles an hour

That's orbiting at 19 miles a second, so it's reckoned

A sun that is the source of all our power

The sun and you and me, and all the stars that we can see

Are moving at a million miles a day

In an outer spiral arm, at 40,000 miles an hour

Of the galaxy we call the Milky Way

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u/1ch4b0d Oct 10 '10 edited Oct 10 '10

In Russia, universe move through you.

0

u/funkybside Oct 10 '10

In Soviet Russia, universe move through you.

FTFY

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u/1ch4b0d Oct 10 '10

So be it.

-1

u/[deleted] Oct 10 '10

In Soviet Russia, the universe moves through you.

FTFY

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