How Are Galaxies Moving Away Faster Than Light?

Article Updated: 23 Dec , 2015

So, how can galaxies be traveling faster than the speed of light when nothing can travel faster than light?

I’m a little world of contradictions. “Not even light itself can escape a black hole”, and then, “black holes and they are the brightest objects in the Universe”. I’ve also said “nothing can travel faster than the speed of light”. And then I’ll say something like, “ galaxies are moving away from us faster than the speed of light.” There’s more than a few items on this list, and it’s confusing at best. Thanks Universe!

So, how can galaxies be traveling faster than the speed of light when nothing can travel faster than light? Warp speed galaxies come up when I talk about the expansion of the Universe. Perhaps it’s dark energy acceleration, or the earliest inflationary period of the Universe when EVERYTHING expanded faster than the speed of light.

Imagine our expanding Universe. It’s not an explosion from a specific place, with galaxies hurtling out like cosmic jetsam. It’s an expansion of space. There’s no center, and the Universe isn’t expanding into anything.

I’d suggested that this is a terribly oversimplified model for our Universe expanding. Unfortunately, it’s also terribly convenient. I can steal it from my children whenever I want.

Imagine you’re this node here, and as the toy expands, you see all these other nodes moving away from you. And if you were to move to any other node, you’d see all the other nodes moving away from you.

Here’s the interesting part, these nodes over here, twice as far away as the closer ones, appear to move more quickly away from you. The further out the node is, the faster it appears to be moving away from you.

This is our freaky friend, the Hubble Constant, the idea that for every megaparsec of distance between us and a distant galaxy, the speed separating them increases by about 71 kilometers per second.

Galaxies separated by 2 parsecs will increase their speed by 142 kilometers every second. If you run the mathatron, once you get out to 4,200 megaparsecs away, two galaxies will see each other traveling away faster than the speed of light. How big Is that, is it larger than the Universe?

The first light ever, the cosmic microwave background radiation, is 46 billion light-years away from us in all directions. I did the math and 4,200 megaparsecs is a little over 13.7 billion light-years.There’s mountains of room for objects to be more than 4,200 megaparsecs away from each other. Thanks Universe?!?

Most of the Universe we can see is already racing away at faster than the speed of light. So how it’s possible to see the light from any galaxies moving faster than the speed of light. How can we even see the Cosmic Microwave Background Radiation? Thanks Universe.

WMAP data of the Cosmic Microwave Background. Credit: NASA

WMAP data of the Cosmic Microwave Background. Credit: NASA

Light emitted by the galaxies is moving towards us, while the galaxy itself is traveling away from us, so the photons emitted by all the stars can still reach us. These wavelengths of light get all stretched out, and duckslide further into the red end of the spectrum, off to infrared, microwave, and even radio waves. Given time, the photons will be stretched so far that we won’t be able to detect the galaxy at all.

In the distant future, all galaxies and radiation we see today will have faded away to be completely undetectable. Future astronomers will have no idea that there was ever a Big Bang, or that there are other galaxies outside the Milky Way. Thanks Universe.

I stand with Einstein when I say that nothing can move faster than light through space, but objects embedded in space can appear to expand faster than the speed of light depending on your perspective.

What aspects about cosmology still give you headaches? Give us some ideas for topics in the comments below.

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22 Responses

  1. Gozlemci says:

    Thanks Fraser for presentation…
    Don’t worry… Hawking, also, does same, once in a while…!

  2. I have never believed the speed of light is a firm limitation of speed. We simply can’t imagine anything moving faster, and we don’t come close to possessing the technology to achieve building light speed spacecraft, but that doesn’t mean lightspeed is a firm limitation of speed.

    Speed is measured by a reference between two objects. Let’s look at three possible (maybe in the distant future) scenarios.

    For the sake of this example, let us suppose we have the technology to create a light speed spacecraft. We launch it to Alpha Centauri. When it accelerates to light speed as referenced from its departing platform of Earth, an astronaut on board walks from the rear of the ship to the front at four miles per hour. Is he not traveling at light speed plus four miles an hour with reference to Earth?

    In the next scenario, we take once again the example of the spacecraft traveling at light speed from Earth to Alpha Centauri. It would be launched presumably at a time when the earth is at a point in its orbit around the sun moving toward Alpha Centauri (to gain the extra 66,000 mph from Earth’s orbital speed). Six months later, the earth is moving away from Alpha Centauri at 66,000 mph. At that point, the reference speed between Earth and the spacecraft is light speed plus 132,000 miles per hour (double the 66,000).

    In the third scenario, we launch one light speed craft toward Alpha Centauri and a second light speed craft to a star system in the opposite direction. Even though these two spacecraft are traveling at the speed of light as referenced from Earth, they are travelling at twice the speed of light with reference to each other. How could they not be?

    I could go on, but I think the point is made that supports the fact that the speed of light is not an absolute limitation of speed, even if we are never capable of creating a spacecraft capable of light speed.

    • Qev says:

      First scenario: the fundamental premise is wrong, because a massive object can’t travel at c. Even if it could, somehow, it has no valid frame of reference, no subjective time passes, and the astronaut -can’t- walk at 4mph. Assuming you meant ‘very very close to the speed of light’, then in the astronaut’s frame of reference he’s walking at 4mph relative to the ship; in Earth’s frame of reference he’s moving ever so slightly closer to c than the ship is. Same with the second scenario.

      Third scenario (assuming ‘speed of light’ is replaced with ‘close to the speed of light’), an Earth observer measures each of them receding from Earth at near-c. Each ship will observe Earth receding at near-c, and the other ship receding at even-nearer-c.

      Relativistic velocities don’t add together simply, because time and space are stretchy. This was Einstein’s big idea.

      • Any information about objects of mass moving at light speed is theoretical at our time in history. Until someone can actually prove what happens, I will continue to believe my own theory, as it makes the more sense in my mind than any other. I’m not presuming I’m smarter than Einstein or anyone else; I perceive light speed as simply adding numbers as one would do with lesser speeds. The Theory of Relativity proposed the perception of an object at light speed from that of an observer. For instance, if you could maintain sight of a person traveling away from you at light speed, they would appear to never age from your point of reference. In actuality, I believe the person would age biologically and normally as perceived by another person on board the same spacecraft. Again, just my thought and theory.

      • Dgeiger says:

        Thank you frasier for article. You asked for ideas for new articles.

        I would state that finding out what happens as you near light speed travel is within our 5 year reach.

        With the possibilty of nano sized machines and a comparitive form of propollsion we can indead test this idea.

        An article on this and a comparitive of new rocket and ship tech including my own would make interesting reading.

    • SteveW says:

      If you could observe a man on a space craft traveling at near c, from his perspective everything would be as normal. But from your perspective his time would be slowed down so much (time dilation) that he would appear motionless. You could not observe his four mph walk to the back of the ship because it would appear to you that his time has stopped.

  3. BrianFraser says:

    Rearrange the gamma equation into its non-local form and you can conclude that EVERYTHING is moving at the speed of light. But that is just for starters.

    Some misconceptions about Special and General Relativity are addressed in the article “Beyond Einstein: non-local physics” (2015). The link is:
    which gives a link to the .pdf file

    • mark_scheuer says:

      Actually, everything IS moving at c through spacetime. Your motion through space, 0<=v<=c, is subject to time dilation [sqrt(1-v^2/c^2)] so the velocity vector of everything in the universe has length c, independent of v, in spacetime. Objects with zero velocity in space are moving at c through time and objects moving faster in space are moving slower in time. Applying a force on the object only causes the vector to rotate but never changes it's length.

  4. TedH says:

    Hi Fraser, my problem is: the distances… the scale.
    It’s easy to say “the distance to Vega is app. 25 Ly but… how far s that? It doesn’t help to know light will need 25 years; the speed of 300.000 km/s is beyond the pictures my brain works with. How long would V’ger need to travel (Hi Captain Janeway) or New Horizon. Their speed is just in the size to work with.
    So my problem is… “Understanding”… working with pictures… not just using a calculator 😉

  5. mark_scheuer says:

    Sorry, guys, but you need to brush up on your Physics (particularly post 1905 physics). It’s okay to use the simple geometrical projection to determine how far away that part of the univers is that is expanding at the speed of light but Special Relativity comes into play long before then in a very simple way – observing the distant galaxy. The redshift equation has the familiar Lorenz contraction term in the denominator (1 – v^2/c^2) so, in trying to observe that distant galaxy, all wavelengths of light emitted by it are redshifted to infinity. You will not be able to observe any galaxy at, or beyond, that point.

  6. ars_186kpersec says:

    We fail to respect the true affect of dark energy. It is what holds the material (a matter of speaking) universe together. We only measure based on the material universe and not what is apart from it. Gravitation only exist because of the difference between our material universe and another existence (universe so to speak) that is not based on matter. It is the forces that hold the our material universe together that we consider, but those forces do not exist in the reality that is absent of time and matter. However, they innervate and we see the affects beyond our measurable universe of time and matter. But theoretically if we disturb the forces (formula) that holds our universe of time and matter together we escape from time and matter to something that may be considered a different dimension, when in fact it is only a different state. We only know what we are but if we are something different than we know that something else…such as what I call the non-material existence. Einstein was close saying gravity was only the bending of the fabric of time and space, but it’s beyond that, there is another existence without time and matter, which is actually the main component. We are only a by-product of it. And why that is that may lead to another question. However, this is how I theorize other intelligent life may travel without the factor of time and space. Similar to a worm hole but not so much as a shortcut passageway between points, but rather into a total different state that is without time and matter. And once you are in it’s terms and out of the fabric formula forces that hold our universe together (for example such as jumping out of water into open atmosphere), travel has a totally different set of rules where there is no time and distance. But if you learn how to control that state of no time and distance then you may be able to instantaneously go from one point to another beyond our understanding of travel.
    So when we measure something that seems to defy the notion that nothing travels faster than the speed of light, we should consider the other element of existence since the two do innervate with each other at some level. Another marker is similar to why we declare radiation particles a “Wavicle,” not able to explain the entire property of it’s behavior because we are not including the affects of the non-material existence. But once we discover how to break out of the fabric (formula) that holds this universe together, we may then consider what is beyond our physical understanding of our material existence.

  7. Elcid says:

    If each galaxie was traveling at 100,000mph , then it would appear as moving faster than light.

    • mark_scheuer says:

      Newton and Galileo might agree but Lorentz and Einstien would not. Relatively speaking, you need some Special help with your understanding.

  8. sergemiatovich says:

    Maybe this will help:

    The theory predicts that large objects can move faster than light, and even more so, how exactly to replicate this behavior by means of technology.

    The popular explanation that “space expands” is weak, and clearly a euphemism for “we have no clue as to why things move faster-than-light”.

    Watch the page above for the math where Einstein’s work is a special case of non-relativistic theory. In general, FTL is possible, but only for large mass. Look at the links at the bottom of the page, you might find them interesting.

    Serge Miatovich
    the author of “Information Field instead of Relativity”

  9. GeneralHQ says:

    Something about this just doesn’t seem right to me.

    I understand that the Hubble Constant H is causing our universe to expand, and because of that, something that is 13.7 billion light years away would be moving away at about the speed of light, and things further away must therefore appear to us to be going faster than light. I get that part.

    But the conclusion that a galaxy almost 13.7 billion light years away will suddenly disappear once it crosses the magic 13.7 billion light year threshold, and eventually all galaxies will do that, does not ring true for me, intuitively. That conclusion makes my gut say ‘wrong!’.

    Therefore, if so, there must be some other mechanism at work to stop that from happening.

    So I was thinking …

    What if, as the universe expands, the actual speed of light increases by the same quantity? What if c (a very large number) were to increase proportionally to H (a very small number) over time? That way, the magic 13.7 billion light year number that limits our observable universe would increase over time, keeping those distant galaxies forever at the edge of our view, and not allowing them to suddenly disappear.

    Would it be even possible to test this hypothesis?

    Is our ability to detect the speed of light c accurate enough to detect that minute of a change?

    If we set up a mirror some distance D from a laser/detector and measured the time T that the light took to make the round trip, waited some time period of time, and repeated the experiment, could we detect the difference in T fine enough to detect changes in c on the order of H?

    The rub is … if the very fabric of the universe were expanding, then D would expand with H (a meter in the future would be ever so slightly longer than a meter today) but if c also changed in exact proportion, then T would remain the same. So, if we run the experiment, and find that T is the same both times, does that mean the c changed with H or that D did not in fact change over time, as H would have said it should?

    My real question is … what kind of test could possibly be done to determine if c is really constant, or if c speeds up over time at the same rate the universe expands? The numbers would be so big, the change so small, would it be possible to detect, even theoretically?

    If c does change as described above, then we will never detect these distant galaxies disappearing. Instead, 13.7 billion years from now, we would still see those distant galaxies at the edge of our visible universe, which would then be 27.4 billion light years – at least by today’s measurement system, but it would still be 13.7 billion light years based on the new measuring system, with the speed of light being twice as fast, and the meter being twice as long.

  10. Zoutsteen says:

    How do we know space isn’t rippling like the ripples in a pond after throwing in a stone?
    (2D surface + 3D ripples representing 3D space + 4D space ripples)

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