[Gozzer101]

As I have learnt it's very difficult to be a stationary observer in space. However we often talk about speeds of certain objects.

For example:
The Earth rotates at 1600 km/hour
The Earth rotates the Sun at around 107000 km/h
The Sun/Solar system moves in a patch of stars at around 70000km/h
We orbit the Centre of the milkyway at around 792000 km/h
We are moving as part of a cluster of galaxies at around 2000000 km/h

Although all these speeds are in different directions it still has to be a "speed"

We measure light to be a speed of 670000000 km/h

As the law of physics if something speeds up, time slows down. That is why light is the speed limit of our universe.

Does this mean then there are other galaxies who's time is different to ours? As some will be moving slower and some faster.

Another question: if we are moving then in certain directions, shouldn't light appear quicker in one direction than others? Say we are moving to point x (1 mil light years away) at 2000000 km/h then the light would have to travel a lesser distance and ultimately in a quicker time to that in the opposite direction?

Finally knowing all these different speeds. If we set off at a high speed in one direction relative to us would we not need to achieve light speed to actually get light speed: as we are already moving in that way anyway, say 5000000 km /h, then we would only need to achieve 670000000 minus 5000000?

[ajb]

Gozzer101, on 6 January 2012 - 01:25 AM, said:

Does this mean then there are other galaxies who's time is different to ours? As some will be moving slower and some faster.

Very generally, different observers will measure different durations of times. You don't need to go as far as other galaxies to see this, experiments here on Earth and in orbit prove this. For example, the GPS system has to take into account relativistic effects that mean that time is measured differently on the satellite as compared to on the Earth .

Gozzer101, on 6 January 2012 - 01:25 AM, said:

Another question: if we are moving then in certain directions, shouldn't light appear quicker in one direction than others?

The speed of light in vacuum as measured by any inertial observer is c.

However what you can have is apparent faster than light speed. For example superluminal speeds have been observed in some radio galaxies and quasars, though this is an optical illusion. Other examples include the possibility of moving a laser dot faster than light This is an "angular" effect and no individual photons travel faster than c. I am sure there are other examples.

[MigL]

Are you sure there is a possibility of moving a laser dot faster than c ( angularily of course )? Would that not imply a superluminal transfer of information, which is,of course, forbidden?

Edit:

Sorry AJB, not thinking clearly this morning. Of course any modulation of the laser still must travel at c, just the position may be moved angularly at superluminal speed. So no actual violatuon of relativity.

This post has been edited by MigL: 6 January 2012 - 08:16 PM

[keep_talking]

Speed is a relative measurement based on distance covered over time.

Time on Earth is relative to Earth and Earth bound objects.

S=D/T

D=SxT

Time on other galaxies would not be the same as time here on Earth. Time (as far as we are concerned) does not move slower or faster based on your location in the universe, but ultimately depends on the mass of objects around you.

More mass = slower time progression

Less mass = faster time progression

Mass is the determining factor of the speed at which time moves. Mass has the ability to slow the "drag" or movement of time (slightly) relative to you.

[swansont]

keep_talking, on 9 January 2012 - 11:08 AM, said:

More mass = slower time progression

Less mass = faster time progression

Mass is the determining factor of the speed at which time moves. Mass has the ability to slow the "drag" or movement of time (slightly) relative to you.

It's more subtle than that. It depends on your gravitational potential, which is the location you have in a potential well. The earth has a much greater effect on clocks than the sun if you are near the earth, even though the sun has more mass.

[Widdekind]

MigL, on 6 January 2012 - 08:14 PM, said:

Are you sure there is a possibility of moving a laser dot faster than c ( angularily of course )? Would that not imply a superluminal transfer of information, which is,of course, forbidden?

Edit:

Sorry AJB, not thinking clearly this morning. Of course any modulation of the laser still must travel at c, just the position may be moved angularly at superluminal speed. So no actual violatuon of relativity.

I understand, that you waving your laser pointer, from one direction, through to another, is a little like you "spraying a burst of photons with your laser AK". And, those photons fly away from you, in all directions, as if you "had detonated a photon flash grenade". I.e. you are the source of all the "information"; and various "targets" can receive their inbound photons, at various different times; but they themselves aren't doing any active communication FTL, they're just "happening to passively receive your laser shrapnel" whenever they happen to do so.