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Good explanation of space/time -- in short, you're always moving in space and time, and the more you move in space, the less you move in time. Vice-versa. Bria
by sabat 16y ago
Good explanation of space/time -- in short, you're always moving in space and time, and the more you move in space, the less you move in time. Vice-versa.
Brian Greene does a pretty good job of explaining all this in the Elegant Universe. If you're into this kind of thing, check it out.
- ars 16y agoBut there is no such thing as moving in space. You can only move relative to another object. You may even move fast relative to one object and slow relative to another, meaning your clock ticks at a different rate relative to each of those objects. There is no absolute clock - you can only compare your clock with someone else's clock.
- sabat 16y agoThere is no absolute clock - you can only compare your clock with someone else's clock. Look, I'm only a layman, but from what I understand, the speed of light is the absolute clock.
- ars 16y agoBut the speed of light can only be measured relative to YOU. So what looks like 90% of the speed of light to you, can look like 10% of the speed of light to someone else.
- deleted 16y ago[deleted]
- sabat 16y agoActually that's just flat-out wrong. Light has an absolute speed. It's the only absolute thing in the universe. It's not relative. And -- this comes directly from Brian Greene -- the speed of light always looks like the speed of light, no matter how fast you're travelling. The speed of light never looks like 10% of the speed of light. It's always the same -- a constant.
- ars 16y agoI didn't say the speed of light - I said 90% of the speed of light. I was refuting the idea of the speed of light as some sort of master clock. But yes, the actual speed of light always looks like the speed of light.
- burgerbrain 16y agoThe speed of light is always 'the speed of light' regardless of your reference frame, however the speed of other objects is purely relative. The 'what' in "So what looks like 90% of the speed of light to you, can look like 10% of the speed of light to someone else." is referring to something travelling slower than the speed of light. A train or bullet perhaps. In different reference frames it can be said that this train/bullet is travelling at different percentages of the speed of light. That's why it gets weird. EDIT: To illustrate this, lets say we're sitting on the earth watching an astronaut. Relative to our position, he is travelling at 1/2 the speed of light. Now, some joker decides to shine his laser pointer at the astronaut. From earth we see the laser beam^ blast past the astronaut at .5c (.5c + .5c = 1c, the speed the laser light is traveling). NOW! from the astronauts perspective! Instead of seeing the laser pass him at .5c, he sees it pass him a nice proper 1c. weird, but it's how the universe works. ^reflecting off spacedust of course :P
- sabat 16y agoThanks for that clarification. But the speed of light can only be measured relative to YOU That's still wrong, though. The speed of light is an absolute; it's not My Speed + the Speed of Light. The person I was who originally responded to me (ars) was trying to say that motion in space is impossible because it's always relative -- apparently even to the speed of light. That's not true; motion is relative to the speed of light, period. And what I had been trying to express (however badly) was that the faster you move relative to the speed of light, the slower you move in time. I think ars was just in a nitpicky mood and was fixating on the particular wording I chose.
- heed 16y agoCan you move relative to a point in space? Even if there are no objects around?
- ars 16y agoNo, because a "point in space" has no definition - without other objects you can't even locate such a point. You can only move relative to other objects.
- fwdbureau 16y agoBut it still makes you wonder how this idea should be understood: Does it mean it is actually impossible to travel faster than the speed of light, or just that you can, but bad things will happen (like coming back too late, or so big that no one will see you, etc)?
- ars 16y agoNo, it's impossible. No matter how fast you go, if you measure your speed (relative to something else of course) you would measure a speed lower than the speed of light.
- kenjackson 16y agoIf it's not possible then how do people escape black holes?
- zephjc 16y agoI think I missed that in my history books
- burgerbrain 16y agoOk, now I'm sure this entire post is the HN equivalent of a 4chan trollscience thread.
- InclinedPlane 16y agoIf you are within the event horizon of a black hole then you cannot escape. Elsewise, from a greater distance you will be able (assuming you have the means) to escape the gravitational pull of the black hole as you would any other object of equivalent mass.
- shangaslammi 16y agoWho are these people you are talking about?