Q: How fast are we moving through space? Has anyone calculated it?

The original question was: Considering the spin of the earth, it’s orbit around the sun, the sun’s orbit around the Milky Way and the Milky Way’s journey through interstellar space, has anyone calculated our speed though the universe?


Physicist: The short answer is “yes”, and the long answer is “well… yes”.

The problem with motion is that “true motion” doesn’t exist.  The best we can do is talk about “relative motion” and that requires something else to reference against.  What you consider to be stationary (what you chose to define your movement with respect to) is a matter of personal choice.  The universe isn’t bothered one way or the other.

Relative to your own sweet self: Zero.  This sounds silly, but it’s worth pointing out.

Relative to the Earth: The Earth turns on its axis (you may have heard), and that amounts to about 1,000 mph at the equator.  The farther you are from the equator the slower you’re moving.  This motion can’t be “ignored using relativity”, since relativity only applies to constant motion in a straight line, and movement in a circle is exactly not that.  This motion doesn’t have much of an effect on the small scale (people-sized), but on a planetary scale it’s responsible for shaping global air currents (including hurricanes!).

Relative to the Sun: The Earth orbits the Sun at slightly different speeds during the year; fastest around new years and slowest in early July (because it’s farther from or closer to the Sun respectively).  But on average it’s around 66,500 mph.  By the way, the fact that this lines up with our calendar year (which could be argued to be based on the tilt of the Earth, which dictates the length of the day) to within days is a genuine, complete coincidence.  This changes slowly over time, and in several thousand years from now it will no longer be the case.  Fun fact.

Relative to the Milky Way: The Sun moves through the galaxy at somewhere around 52,000 mph.  This is surprisingly tricky to determine.  There’s a lot of noise in the the speed of neighboring stars (It’s not unusual to see stars with a relative speed of 200,000 mph) and those are the stars we can see the clearest.  Ideally we would measure our speed relative to the average speed of the stars in the galactic core (like we measure the speed at the equator with respect to the center of the Earth), however that movement is “sideways” and in astronomy it’s much much easier to measure “toward/away” speed using the Doppler effect.  Of the relative speeds mentioned in this post, the speed of our solar system around the galaxy is the only one that isn’t known very accurately.

Relative to the CMB: The Milky Way itself, along with the rest of our local group of galaxies, is whipping along at 550 km/s (1.2 million mph) with respect to the Cosmic Microwave Background.  Ultimately, the CMB may be the best way to define “stationary” in our corner of the universe.  Basically, if you move quickly then the light from in front of you becomes bluer (hotter), and the light from behind you gets redder (colder).  Being stationary with respect to the CMB means that the “color” of the CMB is the same in every direction or more accurately (since it’s well below the visual spectrum) the temperature of the CMB is the same in every direction (on average).

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16 Responses to Q: How fast are we moving through space? Has anyone calculated it?

  1. kopernik says:

    Our problems with system deficits of energy could be solved if we could capture the the differences in torque between two or more bodies.
    For example, take a free standing ton mass on the surface of this planet and cause it to be slowed 100 mph (Don’t ask me how.) relative to the 1000 mph velocity of Earth’s surface. That resulting resistance or momentum could be translated into a form of energy. Of course the amount of energy to do that would be slightly more than the energy we could retrieve. But, if we let the mass catch up slowly with the surface speed, we might end up on the positive side of that energy equation.
    What think ye? K
    Perhaps we could play one momentum source against another –
    [Intra galactic travelers use captured differences in cosmic momentum to propel their craft, but they are secretive about how it is done. ]

  2. James says:

    Why does relativity not apply to circular motion? Lets say…John is spinning in place at 98 revolutions per minute and Jane is beside him spinning at 130 revolutions per minute, when judging either of the individuals ‘speed’ wouldn’t johns speed be relative to janes and janes speed be relative to johns?, also implying both would be relative to a still third party? Obviously this would not work if John was spinning and Jane was running but if both are moving in the same manner why is it not relativity? We can add another element in there and say John was spinning at 98 rpm while standing atop a sitnspin spinning at 400 rpm. I’m no math wiz, hell I haven’t nor do I plan to graduate college yet I am an autodidact and have autism spectrum disorder and in my logic based thought relativity is present regardless of what direction an object moves in.

  3. The Physicist The Physicist says:

    @James
    The laws of relativity do apply to circular motion, it’s just that while velocity can’t be detected (which is what the post is talking about) acceleration can be.
    If you’re flying through space at millions of miles per hours you’d never notice that it’s any different from sitting still. However, if you step on the gas pedal (accelerate forward) or on the brakes (accelerate backward) you will notice the pull. Similarly, when you move in a circle or in any way change direction you’re accelerating and will be able to tell the difference.

  4. Scott says:

    You neglected to mention Siamese cats. They seem to believe (and evidence supports the claim) that all humans revolve around them.

    This answer will get a whole lot more complicated if it turns out “empty” space in fact has structure, as I believe it does.

  5. Matthew says:

    How does the fact that there’s a rest frame of the CMB square with the ‘no preferred frame’ tenet of SR?

  6. Quantum Mechanic says:

    Just out of idle curiosity, what is our heading with respect to the CMB? Or, conversely, where did we “come from” wrt/ the CMB? A constellation or galaxy reference would suit me fine.

  7. The Physicist The Physicist says:

    In the direction of Hydra. Specifically, toward the “Great Attractor“.

  8. Carefree Mathematician says:

    Is it possible to use the CMB to find the approximate area in which everything in the universe originated from? Like, a place, or at least direction of birth. Given the Big Bang, things have been ex

  9. Carefree Mathematician says:

    Is it possible to use the CMB to find the approximate area in which everything in the universe originated from? A place, or at least direction of birth? Given the Big Bang, things have been expanding for quite some time, since the universe was very very small, so shouldn’t there be a “center of the universe,” a point so that the average relative velocities of all particles everywhere is zero? Or failing that, so that the average location of all mass everywhere is right there.

    Also! I’ve seen that a lot of these posts begin with someone asking a question, where do they come from?
    Thanks!! :D

  10. kopernik says:

    You asked – Where did we come from?
    (This is something I wrote about twenty years ago. It’s a little long so you may want to skip it.)
    We Are All Immigrants.
    Yes we are. Every person you have met or will meet is an immigrant. This is not about your parents arriving here from somewhere else, or your grandparents, or even your ancestors going back 10,000 years or more. Every person living or that has lived on this planet (or solar system) is alien to the Milky Way galaxy.
    An outrageous statement? Not if you examine closely our origins. The star that we affectionately call Ol Sol was once part of very small galaxy, a diminutive neighbor to the majestic Milky Way. Our Sun, ensconced in that cozy miniature galaxy surrounded by a number of siblings, was just sputtering into existence several billion years ago. What a proud little galaxy it must to have been. Not very well organized. Just a scattering of average sized young stars. But, it had a grand secret – a plan for creating living things. This quaint collection of stars barely able to call itself a galaxy recognized that at least one of its terrestrial charges had a most rare opportunity for producing plants and animals in many forms, leading perhaps to the development of intelligent life.
    The Milky Way is big. Not the biggest, but clearly it can be classified as among the big. A galaxy can be called big when it encompasses billions and billions of stars, plus other objects, that stretch many light years across space. (If you want an accurate count, say it has a bigllion stars.) It is known that a galaxy grows from a barely distinguishable knot of stars to a super size by two means. First, it makes new stars, generation after generation. Second, after it has attained a certain total mass, its gravitational attraction begins to act on other galaxies within reach, large and small. The large galaxy entices others nearby, especially the smaller ones, into joining its larger grouping. Most low mass galaxies are unable to resist. As these approach and enter the larger assemblage, they are stripped of their stars. Each star, now just one among a ‘bigllion’, is assigned a nondescript place of orbit within the big galaxy. A galaxy gets to be big by repeating many times this process of absorption of smaller units.
    That’s what happened to our progenitor galaxy several billion years ago. While it was still intact it looked over at the dazzling lights of the huge galaxy we call the Milky Way. So organized. So magnificent. So attractive. Great things must be happening there. So irresistible! And, there was this – our home galaxy’s plan for creating Life had hit snag. The basic chemical compounds had been assembled on several of its planets, carbon compounds, even a few amino acids. But, the physical conditions were just not right. For example, the plan called for liquid water. There was plenty of H2O, except that on the various planets it was either hot steam or frozen solid, and almost always mixed with the wrong chemicals. Then there were the missing elements. Our little galaxy had gleaned from space a few precious components during its travels. Still, it lacked certain heavier elements. These could only be produced by super novas (exploding giant stars), rare in a small galaxy. Over in the Milky Way these chemicals were abundant.
    Life! Was it worth the loss of independence? Loss of self identity for this small galaxy? Indeed, yes! For it brought into being something very uncommon, perhaps unknown in that much greater galaxy. To complete its mission this toddler of a galaxy had to sacrifice its very self and wholeness. Scientists assume that the spontaneous emergence of living things requires a vast network of opportunities and a high degree of complexity, both available for a long span of time. Not so? Well, our little galaxy and its special star did it in record time. The Milky Way does not deserve credit for this accomplishment. As far as is known, the Milky Way has not produced advanced life forms. Indeed, during its early turbulent times this now colossal galaxy would have snuffed out any attempts at life. Instead of turning our detectors for intelligence onto the giant galaxies, perhaps we should be looking at those small mom and pop galaxies out there, alone in dark space, dreaming big dreams.
    You may have noticed the references in this article to our small parent galaxy as ‘it’. It does not have a name because scientists feel ‘it’ has lost all identity as a galaxy. Due to the angle of entry into the Milky Way, our star along with the remnants of that lost galaxy obit the giant Milky Way in a way that takes this motley group of survivors a few light years above the plane of the galaxy and then a few light years below, while shuttling between the Sagittarius Arm and Perseus Arm of the M.W. galaxy. Other captive dwarf galaxies have been given names, e.g., Canis Major and Complex H., Sagittarius and UMajor, and even Boo.
    After nearly five billion years we may no longer think of ourselves as immigrants; still, our history endures. Like all new generation families we have little or no recollection of the ‘old country’. Even so, doesn’t that little galaxy that gave us life deserve our appreciation? Come on folks, People of Earth, let’s give that unknown and forgotten galaxy a name. (Examples, Atlantis, or Salvitar, or Maia.)
    Send your suggested name for that lost, but not forgotten galaxy to
    Ask a Mathematician . . . .
    Kopernik2

  11. The Physicist The Physicist says:

    @Carefree
    The CMB comes from every direction. Rather than indicating the location of the Big Bang, it actually provides evidence that the Big Bang didn’t happen in a particular location, but happened everywhere. There’s a post here that talks about that a bit.
    The questions on the site come from folk lucky enough to know us personally or who showed up to the booth at Burning Man, or are sent in by email. Mostly email. The address is near the top of the homepage.

  12. Amateur Number Cruncher says:

    It’s generally thought that Dark Matter/Dark energy makeup some where around 96% (it does vary a little depending on who you read). From what I understand, which is probably very little, dark matter/energy pervade what we think of as empty space. So, if you were moving through “empty” space at whatever speed then wouldn’t you be moving relative to the dark matter/energy? I realize dark m/e is really hard to perceive, but it is still there right?

  13. The Physicist The Physicist says:

    @Number Cruncher
    Yup!

  14. Wondering Joe says:

    Our path through static space can be compared to a type of cosmic “tilt-a-whirl”! So if (just taking into account the rotation and the orbit around the sun of the earth) we are travelling at 65500 mph at high noon and accelerating to 67500 mph at midnight then decelerating back to 65500 mph every 24 hours, why don’t we experience these forces?

  15. The Physicist The Physicist says:

    @Wondering Joe
    We do! The rotation of the Earth (which accounts for the changes in speed you mention) causes a slight bulge at the equator. However, this centrifugal force just decreases the effective strength of gravity close to the equator by a tiny amount.

  16. Shaw says:

    @kopernik Dunning-Kruger

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