Hubble Deep Field. Image credit: Hubble

How Can Galaxies Recede Faster than the Speed of Light?

Article Updated: 24 Dec , 2015

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Question: How Can Galaxies Move Away Faster Than Speed of Light?

Answer: Einstein’s Theory of Relativity says that the speed of light – 300,000 km/s – is the maximum speed that anything can travel in the Universe. It requires more and more energy to approach the speed of light. You could use up all the energy in the Universe and still not be traveling at light speed.

As you know, most of the galaxies in the Universe are expanding away from us because of the Big Bang, and the subsequent effects of dark energy, which is providing an additional accelerating force on the expansion of the Universe.

Galaxies, like our own Milky Way are carried along by the expansion of the Universe, and will move apart from every other galaxy, unless they’re close enough to hold together with gravity.

As you look at galaxies further and further away, they appear to be moving faster and faster away from us. And it is possible that they could eventually appear to be moving away from us faster than light. At that point, light leaving the distant galaxy would never reach us.

When that happens, the distant galaxy would just fade away as the last of the photons reached Earth, and then we would never know it was ever there.

This sounds like it breaks Einstein’s theories, but it doesn’t. The galaxies themselves aren’t actually moving very quickly through space, it’s the space itself which is expanding away, and the galaxy is being carried along with it. As long as the galaxy doesn’t try to move quickly through space, no physical laws are broken.

One sad side effect of this expansion is that most of the galaxies will have receded over this horizon in about 3 trillion years, and future cosmologists will never know there’s a great big Universe out there.

You can read more about this in an article I did called the End of Everything.

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John Tomassoni
Guest
April 22, 2008 3:43 PM
Regarding: “How Can Galaxies Recede Faster Than the Speed of Light” It was stated: “And it is possible that they (galaxies) could eventually appear to be moving away from us faster than the speed of light. At that point, light leaving the distant galaxy would never reach us. When that happens, the distant galaxy would just fade away as the last of the photons reached Earth, and then we would never know it was ever there”. I do not understand why its light would never reach us — If light travels at the speed of light, then it seems that it reach us eventually no matter what speed the galaxy is traveling. Its frequency would certainly be reduced… Read more »
Don Don
Guest
April 22, 2008 11:38 PM

The light wouldn’t reach us because light has had only 13.7 billion years to reach us. Because of this it may be possible that something is 15 or 20 billion light years away and we wouldn’t know about it since it’d take a few more billion years to reach us.

The expansion of the universe is very similar to baking cookies. Pretend that galaxies are the chocolate chips in the cookies- when you cook them the chips don’t move away from each other. It’s the dough expanding. Space works exactly like this.

Chuck Lam
Guest
Chuck Lam
April 23, 2008 5:21 AM
Hmm . . . interesting question. I suspect that space itself might be static in shape. That is galaxies travel through it rather than with it. Why are galaxies literally flying apart at an accelerated rate? This phenomenon could be driven by the equivalent of “like polarity repulsion” contrary to gravitational attraction. So . . . “how can galaxies recede at a rate faster than the speed of light?” Why not! We know or at least we think we know that a recession rate of red shift .one might represent an actual barrier crossed by receding faster than light never to be seen again.galaxies. If this is close to factual, this suggests the observable portion of our universe… Read more »
TJ
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TJ
April 23, 2008 1:32 AM
Tomassoni is quite right (the first part at least). The distance from us at which galaxies *appear* to recede at the speed of light defines the Hubble radius. We see galaxies further away than that all the time. We see them in the past. We will see them in the future *unless* the expansion of space in between is too fast. Forget about dark energy for a moment and eventually, a photon from a galaxy receding faster than c would cross into our “Hubble sphere” and actually be moving toward us instead of away. And it would eventually reach us. Dark energy makes it more complicated. If the Hubble radius is decreasing (because of the accelerated expansion) faster… Read more »
Ry
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Ry
April 23, 2008 7:22 AM
I am just trying to understand this my own way but could this theory by analogous to the following bad dream I have had? There is one hallway (space/time) and two doors appearing at either end of the hallway. What I will call door number one will represent a distant galaxy, and door number two at the other end will be observers on earth, earth itself or our galaxy, it doesnt matter which one. Now in this dream I represent light itself. As I escape through and away from door number one (distant galaxy), I run down the hallway (light traveling through space time), but due to this bizzare dark energy the hallway itself actually starts elongating (expanding).… Read more »
Chuck Lam
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Chuck Lam
April 23, 2008 3:36 PM

To Dark Gnat, Isn’t it generally accepted that red-shift is as much a measure of recessional speed as is this thing you call expansion?

Dark Gnat
Guest
Dark Gnat
April 23, 2008 11:51 AM

The light from the farthest galaxies is red shifted. Some are so red shifted that we can only get a good look at them through infra-red imaging.

The reason for the red-shifting is because the space between the galaxies and us is expanding, and the waves are spreading apart. The radiation from the earliest times that we can detect is in microwaves (cosmic microwave background radiation).

Eventually, the farthest galaxies will be so far away, that the we won’t be able to detect the whole wavelength, and it will thus be invisible.

Andy
Guest
Andy
April 25, 2008 10:14 AM

A simpler way to look at it is this: We look at ourselves as stationary and “see” them receding faster than the speed of light. From their point of view, we are the ones receding at a superluminal velocity. Either way, we are lost ot each other.

Wolfgang HEBEL
Guest
Wolfgang HEBEL
May 10, 2008 1:05 PM

Our traditional model of an expanding Universe is probably on the wrong track. See my study “The Mystery of Life – Does science hold the key?” (www.dwv-net.de).
Sincerely, Wolfgang

ozgur alci
Guest
ozgur alci
June 10, 2008 6:38 PM

if galaxies were getting far away from us at the speed of light we would never lose the light of them because they can only speed up to the speed of light, only change would be the picture we get, simply i would be just older.

schrodinger
Guest
schrodinger
June 22, 2008 11:17 PM
Since light does not require an “ether”, it propagates freely and independently of space, meaning it propagates free of any expansion of space. Even if the apparent velocity of expansion reaches or exceeds the absolute velocity of light, light will eventually reach us from even the most distant objects in the Universe. The only way to outrun light is to exceed the absolute velocity of light, which is impossible. Suppose the velocity of a bullet to be 1000 meters/second. Now two automobiles are speeding away from each other, each travelling at 600 meters/second. Their net velocity of 1200 m/s exceeds the velocity of the bullet. Now fire a gun from one auto, directed at the other. Do you… Read more »
The Teddy
Guest
The Teddy
October 9, 2008 3:03 PM

I thought that according to theory, if you were to look at someone moving at the speed of light, they would appear to be staying still. Wouldn’t they be in another dimension were they to hit the speed of light, thus being in another dimension altogether? The galaxy would not be able to recede at light-speed otherwise it would cause us to travel to another dimension.

Ivor Clark
Guest
Ivor Clark
December 3, 2008 1:30 AM

I like the idea of being a primordial photon. As I travel across the expanding Universe just behind me is the Big Bang, where I came from and just ahead of me is the Big Crunch, where I am heading to. In your reference frame my time stands still, and the Universe compresses to Zero distance in my line of direction. We perceive our Universe as it is simply because we cannot travel anywhere near light speeds for these effects to happen to us. As Einstein put it “Everything is just an illusion”. “Time and distance have no meaning to the photon. We “see” our Universe the way it is because of our frame of reference.

Mahone
Guest
Mahone
December 19, 2008 9:15 AM

This is the dilemma to me. To say that only space is expanding at + C and the matter/galaxies it contains are not makes no sense. A bubble of space moving at + C, containing a galaxy within it, means that the contained matter is going +C; at plus SOL matter supposedly becomes infinitely dense! Also, at C, time essentially stops. Therefore, beyond the speed of light we have: infinite density for matter (infinite compression as in a singularity?), time stops, and we enter a zone of effects were we can’t even make a good guess at what happens. Is my logic faulty here? Please send me your reply at: [email protected]

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