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How Space Can Expand Faster Than the Speed of Light
StartsWithABang writes You know the fundamental principle of special relativity: nothing can move faster than the speed of light. But space itself? That's not a "thing" in the conventional sense. Two years after coming up with special relativity, Einstein devised the equivalence principle, and thus began the development of general relativity, where space itself would have properties that changed over time, responding to changes in matter and energy. This includes the ability for it to expand, even faster than the speed of light, if the conditions are right.
Some time last year I wrote a lengthy explanation of what exactly "space itself" means. It's not really a physical thing, but rather a result of a particular choice of coordinates which turns out to be very practical.
http://science.slashdot.org/co...
"Speed" is just distance divided by time. Both distance and time are defined by agreeing on a particular set of coordinates. In our immediate neighborhood there isn't much discussion about what we mean, apart from which unit to use (miles, km,...) but on intergalactic distances in an expanding universe there are several different, perfectly valid choices of coordinates that yield wildly different results for distance, speed, simultaneity, etc... You can choose a coordinate system that obeys special relativity and find that nothing goes faster than the speed of light relative to us. But with different coordinates, the speed of light itself is not tied to our location but rather to local "space". That's just a mathematical convention because it turns out to be more convenient that way. Anyway, I explained it all in detail in the above link.
The fact that time slows for you as you go faster; doesn't this imply that if you could travel at the speed of light, then you could reach anywhere in the universe in 0 relative (to you) time? I mean the thing you were aiming for might be gone by the time you got there, but still. If that EmDrive thing is a real thing, doesn't long distance space travel become a real possability?
Correct me if I'm wrong, but do we even know how big "space itself" is? I mean sure, we have an idea as to how much of it we can see thanks to radiation and whatnot, but who's to say it's not actually bigger than we ever thought? We live at the bum end of the galaxy, who's to say we don't also live at the bum end of a universe that expands twice or a hundred times farther in the other direction than we ever considered?
well because of the patterns we can measure in the cosmic microwave background we can measure the 'flatness' of space itself. Positive and negative curvature imply a finite size to the universe. As it is we have measured that space is at least 1000 times the volume we can 'see' in the visible universe. Possibly its infinitely large.
And who's to say that all of what we can see actually belongs to our universe and isn't just spill-over from a bunch of intersecting universes?
Because we can measure distance we know that we are sitting at the 'center' of the visible universe as it is isotopic (the same in every direction). Technically you yourself live across a nearly infinite number intersections of universes that were in contact during the early inflation times, but separated and only now are reconnecting. Your own two eyes each peer into a slightly different universe where the percieved 'center' of the visible universe is offset a few inches. Each eye can 'see' a few nano light seconds beyond the visible horizon of the other.
And who's to say our big-bang-bubble-universe isn't just one in countless universes expanding all throughout space itself?
actually about as many cosmologists agree this is the case as climatologists agree on anthropogenic climate change. It appears highly plausible if not actually true.
What is space itself anyway? Isn't it just an arbitrary construct created to give ourself some sense of importants, some sense of being in a specific place and time, because our simple brains can't cope with not knowing where we are and how the universe revolves around us?
Space itself is likely just a mathematical construct. It would explain why math works so frekishly well at explaining the physical world while no AI/purpose driven explanations make any sense at all. It's even possible that all possibilities of our physical laws (or even combinations of all possible laws) 'exist' statically and eternally with only the perception of time and choice when you find yourself inside a particular one, continually only ever sensing a tiny fraction of it. The the theory of everything may just be the ultimate ensemble theory.
What is the question about life, the universe and everything, anyway?
It's actually plausible the only 'purpose' of life is to increase entropy faster that without it. Like fire burning or water running down hill it simply is a pathway to diffuse energy. It's why all life has a version of eating and pooping. There is no 'purpose' but that actually is the best scenario for us all - we have the freedom to make our own purpose. The computational complexity of the universe itself is so vast free will really feels free, it is an amazing experience and one i have great trouble topping in my imagination.
Search for susskind on youtube. He is a famous professor at Stanford who not only was one of the original creators of string theory but also beat up Stephen hawking on the nature of black holes and got him to admit he was wrong. I recommend special and general relativity series, also the one on inflation. He avoids the arcane and makes physics pedestrian yet provides the mathematical basis for each topic. He gets serious props in my opinion for freely sharing his knowledge online, giving anyone the ability to essentially audit his classes.