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Hi, I've bought PW recently and began reading it just yesterday. I have felt some doubts while reading it, since I haven't had any physics since I left high school and that has been a long time ago. Also, all this astrophysics always a tad mind-boggling to me. So far I have 2 sets of questions (but I'm onlin in the 2nd chapter now)
1)
In the book, Michio Kaku says the universe expanded at a rate faster than light, but that this does not contradict the limit on light's velocity because it was the empty space that was expanding, not an object that was moving. I'm sorry, but I don't understand this. How is it that the empty space is expanding? Are we saying that the objects in it are fixed but that they being pushed by an ever growing sort of tissue between them, that happens to be "empty space"? If it is not this, how can we argue that the objects are not moving, and that they are not moving beyond the speed of light although they're expanding faster than that?
2)
MK also says at another point that we now have a device that photographed objects 13 x10^9 light-years away (I prefer using scientific notation since 'billion' is a highly ambiguous term depending on where you're from). That means that we have just now captured the light of an object as it existed that time ago. I understand the basic idea but I can't visualize it very well. So, in the big bang, there is a fixed point in space and time (let's call it t=0) and then everything starts expanding from then. Eventually, our own location expands to. First, does this mean the universe is some kind of sphere or ellipsoid that expands radially from a center? But then, some objects must travel faster than others, right? why do they travel at different speeds? Ok, so Earth has not appeared at the time of the big bang, but some thousand million years after. When it forms, it is already a fair distance away from the origin point of the big bang, let's say the centre of the sphere. Then when we captured this light, were we looking in the direction of the center of the universe, say, towards the opposite direction that our galaxy is traveling in? And does that mean that whatever light was caused by that explosion is still there, stopped in place? But shouldn't have light traveled too? And if it did, then is it truly "behind" us? Shouldn't it have sped away ahead of the objects that were meanwhile expelled?
I'm sorry if this is disorganized, but I have real difficulty around these concepts. Perhaps some animation of this expansion of the universe would be useful, if someone knows where I can find it.
Thanks if any of you can help me in here.
1)
In the book, Michio Kaku says the universe expanded at a rate faster than light, but that this does not contradict the limit on light's velocity because it was the empty space that was expanding, not an object that was moving. I'm sorry, but I don't understand this. How is it that the empty space is expanding? Are we saying that the objects in it are fixed but that they being pushed by an ever growing sort of tissue between them, that happens to be "empty space"? If it is not this, how can we argue that the objects are not moving, and that they are not moving beyond the speed of light although they're expanding faster than that?
2)
MK also says at another point that we now have a device that photographed objects 13 x10^9 light-years away (I prefer using scientific notation since 'billion' is a highly ambiguous term depending on where you're from). That means that we have just now captured the light of an object as it existed that time ago. I understand the basic idea but I can't visualize it very well. So, in the big bang, there is a fixed point in space and time (let's call it t=0) and then everything starts expanding from then. Eventually, our own location expands to. First, does this mean the universe is some kind of sphere or ellipsoid that expands radially from a center? But then, some objects must travel faster than others, right? why do they travel at different speeds? Ok, so Earth has not appeared at the time of the big bang, but some thousand million years after. When it forms, it is already a fair distance away from the origin point of the big bang, let's say the centre of the sphere. Then when we captured this light, were we looking in the direction of the center of the universe, say, towards the opposite direction that our galaxy is traveling in? And does that mean that whatever light was caused by that explosion is still there, stopped in place? But shouldn't have light traveled too? And if it did, then is it truly "behind" us? Shouldn't it have sped away ahead of the objects that were meanwhile expelled?
I'm sorry if this is disorganized, but I have real difficulty around these concepts. Perhaps some animation of this expansion of the universe would be useful, if someone knows where I can find it.
Thanks if any of you can help me in here.