I always under the impression we couldn't find out, we could only judge it in relation to another point, say we are moving at speed A to Galaxy 1 but at speed B to Galaxy 2
Consider a light beam (or a photon) being sent from Earth to a detector on the Moon.
Our galaxy has to be moving and in some direction through the universe (or extremely likely to be) as others are coming towards us (andromeda) and others are moving away (not including the expansion of the universe where all distance galaxies appear to be moving away)
I was thinking if we sent two light beams to a detector on the moon at opposite points on the earth then the time it would take to get their would change. Why? Because if we are moving in relation to the universe in the direction of X then if we sent the beam while the moon was parallel to Earth and directiom X then the distance the photon has to travel has increased: for example: the photon travels 100 m (for arguments sake we will say it takes 1 second to do this) towards the moon yet in relation to the universe the moon has travelled 5m further away (distance it travels in 1 second) from the original destination the photon was sent (not earth as this will be moving in the same direction and speed, so a point in space)
If we sent the beam from the opposite side of the earth then the distance it has to travel to the detector will decrease and so it should arrive quicker, even though light hasn't travelled any quicker it just appears to (for every 100m the photon travels, the moon gets 5m closer)
My question: Using many points to send a beam and using calculations could we then determine what direction and speed we are travelling through the universe?
Please don't confuse the beam being sent to the moon and us measuring the time it takes for it to appear on the moon (or for it to be reflected back to us) as this would cancel out the affect. Why? Because on the return journey, say use are moving in direction X then on the return journey (moon to earth) it would be quicker as the distance it has to travel has decreased.
If my reckoning is wrong then please tell me why?