A Briefer History of Time

1) Quantum effects are generally only significant at the atomic level and smaller. Gravity is generally only important where one of the things is at least as big as a mountain and the other is at least big enough to see.

2) There is nothing we can measure the speed of the Milky Way against, and the concept of the speed of the universe doesn't make sense, so the furthest you can go is the speed of the train relative to the centre of the Milky Way. As you read more about relativity you will find out why.

 

Ofcourse you could use relativity to measure some absolute speed as against the speed of the universe but the problem here is we don't even know how big the universe is because the speed of light permits us to see further then some distance x.So if we don't know the end of the universe nor do we know what's "outside" of it if there even is such outside then talking about some absolute speed is useless all we can do is talk about speed of object x versus speed of object D etc.All we are doing actually is comparing speeds from different objects to different other objects and or backgrounds.

And by the way be careful with all that evolution theory and everything that surrounds it as some areas of it are not as known as others , there are many unknowns etc , so you have to have a pretty good background and critical thinking to understand all the facts and all the parts which are still just a good guess. That makes a huge difference as there are things we know for sure (have measured them or made experiments) and things which we are not so sure but we have a say good guess or as science calls it level of certainty.

 

We can measure the velocity of the Milky Way against the Cosmic Microwave Background. It turns out to be on the order of 550 km/s in a particular direction. See http://arxiv.org/abs/astro-ph/9312056 .

 

Yes it was a bad answer (although the figure for 550km/s is not the right one for the Milky Way's motion I believe). We can measure the our speed relative to the universe, but (I assume that) the reason Hawking says there is "no such thing as absolute speed" is that someone else moving (very rapidly) relative to us would measure us as having a different speed.

 

"What exactly is size relative to ?"

I think this part of it is a very profound question deep in the center of physics.
It seems very interesting that the principals of interaction change with the size of the actors.
It lends a sense of "absolute size" to a field where absolute time and absolute space don't exist.
Right now it seems that "size" seems to be relative to the theories with which these things are described.

 

Well it's probably wise to scale something to the smallest size we have (Planck) rather than the biggest possible out there which we don't know of because we have no way of knowing that...

 

There is an absolute size: Atoms. An atom of any given element (at low energy state) can only ever be one fixed size. You can put energy in and make the atoms occupy higher orbits, but these are also a fixed and limited set of sizes. Anything smaller than a hydrogen atom can't be an element.

 

No it is YOU that is making the anthropocentric assumption by insisting that our universe exists in the same spatial dimensions as every other universe (in order for the notion of speed within a multiverse to make sense). Most people that have given this serious thought realise that there is no reason for this to be the case, and that is why we say that "speed relative to the multiverse" has no meaning, not because we are denying the possibility of the existance of other universes.

Nobody is saying this. What changes with the size of the actors is the SIGNIFICANCE of different interactions. Within an atom, gravity is insignificant but quantum mechanics and other interactions become important. When you throw a ball in the air, nothing really matters except gravity and air resistance.