Do the past and future exist?
This is a difficult question to even ask because the word “exist” carries with it some “time-based assumptions”. For example, if you ask “does the Colossus of Rhodes exist?” the correct answer should be “it did, but it doesn’t now.
The problem with the way the word “exists” is used is that it implies “now”. So, in thatsense: no, the past and future don’t exist (by definition). But big issues start coming into play when you consider that in relativity (which has given us a much more solid and nuanced understanding of time and space) what “now” is depends on how you’re physically moving.
Here’s what’s interesting with that: if we can say that the present and all those things that are happening now exist (regardless of who’s “now” we’re using), then we can show that the past and future exist in the exact same sense.
Again, if we define things that are can be found “right now” as existing, and we don’t care whose notion of “right now”we use, then the future and past exist in exactly the same way that the present exists.
It seems as though what’s going on in the present is somehow important and “more real” than what happened in the past. But consider this; we never interact with other things in the present. Because no effect can travel faster than light the best we can hope for is to interact with the recent past of other things. For example, since light travels about 1 foot per nanosecond, the screen you’re seeing now is really the screen as it was a nanosecond or two ago. Hard to notice. In relativity everything (all the laws, cause and effect, that sort of thing) is “local”, which means that the only thing that matters to what’s happening here and now is everything in the “past light cone” of here and now. That’s the blue bottom triangle of the top picture.
What’s happening now in other places is totally disconnected. For example, Alpha Centauri is about 4 light years away, and while things are certainly happening there “right now”, it won’t matter to us at all for another four years. Even though those events are happening now, they’re exactly as indeterminate and hard to guess as the things that will happen in the future. The point is that “now” does extend throughout the universe, but that doesn’t physically mean anything, or have an actual effect on anything.
So if things in the past and future exist in the exact same way that things in the present exist, then doesn’t that mean that they’re fixed? If my future is the past for someone else who’s around right now (and necessarily moving very fast like in the last diagram), then does that somehow determine the future? The answer to that question is: it doesn’t matter, but for two interesting reasons.
First, if you consider someone else who’s around “now”, then they’re not in your past light cone and they’re not in your’s (in the top diagram the “nows” are always in the purple regions). That means that, for example, some of Bob’s future will be in Alice’s past, but neither of them can know what that future holds until they wait a while. Bob has to wait until he’s “in the future”, and Alice has to wait for the signal delay before she can know anything. Either way, the events of Bob’s future are unknowable regardless of who (in Bob’s present) is asking. The future is a lock and the only key is patience.
The problem with the way the word “exists” is used is that it implies “now”. So, in thatsense: no, the past and future don’t exist (by definition). But big issues start coming into play when you consider that in relativity (which has given us a much more solid and nuanced understanding of time and space) what “now” is depends on how you’re physically moving.
Here’s what’s interesting with that: if we can say that the present and all those things that are happening now exist (regardless of who’s “now” we’re using), then we can show that the past and future exist in the exact same sense.
Again, if we define things that are can be found “right now” as existing, and we don’t care whose notion of “right now”we use, then the future and past exist in exactly the same way that the present exists.
It seems as though what’s going on in the present is somehow important and “more real” than what happened in the past. But consider this; we never interact with other things in the present. Because no effect can travel faster than light the best we can hope for is to interact with the recent past of other things. For example, since light travels about 1 foot per nanosecond, the screen you’re seeing now is really the screen as it was a nanosecond or two ago. Hard to notice. In relativity everything (all the laws, cause and effect, that sort of thing) is “local”, which means that the only thing that matters to what’s happening here and now is everything in the “past light cone” of here and now. That’s the blue bottom triangle of the top picture.
What’s happening now in other places is totally disconnected. For example, Alpha Centauri is about 4 light years away, and while things are certainly happening there “right now”, it won’t matter to us at all for another four years. Even though those events are happening now, they’re exactly as indeterminate and hard to guess as the things that will happen in the future. The point is that “now” does extend throughout the universe, but that doesn’t physically mean anything, or have an actual effect on anything.
So if things in the past and future exist in the exact same way that things in the present exist, then doesn’t that mean that they’re fixed? If my future is the past for someone else who’s around right now (and necessarily moving very fast like in the last diagram), then does that somehow determine the future? The answer to that question is: it doesn’t matter, but for two interesting reasons.
First, if you consider someone else who’s around “now”, then they’re not in your past light cone and they’re not in your’s (in the top diagram the “nows” are always in the purple regions). That means that, for example, some of Bob’s future will be in Alice’s past, but neither of them can know what that future holds until they wait a while. Bob has to wait until he’s “in the future”, and Alice has to wait for the signal delay before she can know anything. Either way, the events of Bob’s future are unknowable regardless of who (in Bob’s present) is asking. The future is a lock and the only key is patience.
Comments
Post a Comment