• Question: How is it that galaxies that are red shifting appear to be moving away at light speed or faster when the laws of physics state that time travel is impossible?

    Asked by yourmum to Meeks, Pete, Stephen, Steve, Tom on 23 Jun 2010 in Categories: .
    • Photo: Stephen Curry

      Stephen Curry answered on 19 Jun 2010:

      I don’t think there’s any good evidence that things can actually travel faster than light. But in an expanding universe, the further apart two object are, the faster they are moving apart (you can test this by drawing pairs of dots on a balloon and blowing it up.

      So if two galaxies are moving apart from one another, each at 0.75 the speed of light, I suppose their relative speed of separation would be 1.5 times light-speed.

      But all that is mere conjecture on my part – I’m not an astrophysicist.

    • Photo: Tom Hartley

      Tom Hartley answered on 19 Jun 2010:

      I answered a similar question earlier, and I’m going to say the same thing even though another student came back with a very complicated quote suggesting I should think again. (Health Warning: I Am Not A Physicist)

      I don’t think they are receding at light speed.

    • Photo: Pete Edwards

      Pete Edwards answered on 21 Jun 2010:

      As you know distant galaxies, like our own Milky Way are carried along by the expansion of the Universe, and will move apart from every other galaxy. As you look at galaxies further and further away, they appear to be moving faster and faster away from us. So is it possible that they could eventually appear to be moving away from us faster than the speed of light? Don’t panic Einstein’s theory is not broken! 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.

    • Photo: Marieke Navin

      Marieke Navin answered on 22 Jun 2010:

      It is an *optical illusion* usually seen in the jets of quasars and radio galaxies, called superluminal motion

    • Photo: Steve Roser

      Steve Roser answered on 23 Jun 2010:

      do they? I’m not sure that is true.