What's the Fabric of space made out of?

You're welcome buzsaw. Now, can you please try answering a simple question?Here are four examples of combined velocities.

1. An eagle flies at 100 km/hr down the aisle of an aeroplane flying at 900 km/hr. The speed of the eagle from the ground is 999.999999999999923 km/hr.
2. A very high speed bullet is fired at 40% of the speed of light down the aisle of a spacecraft flying at 50% of the speed of light. The speed of the bullet from the ground is 75% of the speed of light.
3. An even faster bullet is fired at 75% of the speed of light down the aisle of a spacecraft flying at 75% of the speed of light. The speed of the bullet from the ground is 96% of the speed of light.
4. A laser beam is fired down the aisle of a spacecraft flying at 90% of the speed of light. The photons are travelling at the speed of light; whether they are measured from the ground or from inside the spacecraft.

You’ve used the word logical a lot. Tell me, are the statements above logical?The idea is to determine what logical really means when you say something is or is not logical. Even if I disagree with your answer, I promise not to merely laugh at you. I know that this stuff is bewildering, but it will really help if you can just answer the question clearly.Thanks -- Sylas

Caution... if you speak about what is "seen", then actually you do see the second hand ticking more slowly. Suppose a photon leaves the watch at a certain instant. Another photon leaves when the second hand has ticked off another second. The second photon has further to travel than the first, and so arrives more than a second after the first. You see the clock ticking off seconds more slowly.In fact, this is one of the lines of evidence that redshift really is due to expansion of space, and not due to loss of energy by some tired light effect. Supernova light curves have a characteristic decay time; but those which have a high redshift decay much more slowly. This is due to the same slowing effect as with the watch.You also get a similar effect with recession due to local motions in space, and for the same reason. Photons leaving later have further to travel, and take longer to get here. This is actually a reasonable correspondence over small scales (small in comological terms!) but this does break down over billions of parsecs.Redshift can be seen in this way as well. A photon is emitted with a certain frequency. We see it "slowed down" (reduced frequency) which is the redshift.One thing to bear in mind that in general relativity, notions of distance and of velocity over large scales are not well defined. Comparing cosmological expansion to local motions is a good approximation at small scales -- and this makes it hard to explain the difference between local motions and expanding spaces in terms of observation. A full explanation in terms of local motion does fail, as you say; and we do need to use expansion of space to fit the observations.Cheers -- Sylas