does the past exist?
Recently I argued that time travel into the future just doesn't make sense, given a reasonably cogent understanding of what "the future" is. It may be that traveling into the past is just as absurd. Jason of Jason's tech blog poses a question:
what makes you think the past exists?
I mean, sure, we lived through it, and will agree on much of what occurred there, but why should it still exist once we’ve passed it? We can’t predict the future because of quantum uncertainty. That same uncertainty would make it impossible to “predict” (or reconstruct) the past, even given perfect current data (also impossible, due to quantum uncertainty).
In loose analogy with computer terms, where is the data written? The program ran, but what makes you think anyone saved the run? All the information in the universe is describing the present state of the universe. There isn’t room for the information of past states to exist.
The question does the past exist? is a snappy attention grabber, but it's not really at the heart of Jason's question. His point is that the past may be unrecoverable for the same reasons that that the future is unknowable: quantum uncertainty. To put it another way, we can't know the past because it doesn't exist any more.
I previously described the past as fixed, and the future as fluid, but if you can't know the past completely, then how fixed is it, really? Both future and past trail off to infinity with increasing uncertainty. And the future is at least partly knowable: I can tell you when the moon will rise in twenty years time, what the map of earth will look like (the same as it is today), and the approximate population of Tokyo. I can even guess some of the headlines of the day: "school leavers sit final exams", "election day approaching", "tragic murder in suburbia".
But the two differ in symmetry in certain interesting ways. For example, the law of entropy says that disorder has a directional slope from past to future. And from a human perspective, unless you are Gil Grissom investigating a crime scene or a historian reconstructing an ancient battle, you do not typically entertain multiple versions of the past in your mind. By contrast, we constantly juggle alternative scenarios of the future.
As with the future, we cannot know the past perfectly, but this does not mean it doesn't exist. Electrons exist in probability clouds, and we're happy to declare that electrons exist. The same applies to the past. To the extent to which it has form at all, it exists.
10 comments:
Some would say, that the past is a present memory, and the future, as a present expectation. Both seem tangible. Perspective is the only key to knowing more than one state of such. Such is my opinion. Steve Minnick, paint-pro@hotmail.com
Hello.
A point that sticks in my mind from one of Brian Greene's great books is that the concept of a "now" in time is completely foreign to physics and mathematics. Science can describe a system within the spacetime continuum, but gives us no basis for bestowing upon any particular moment the special dignity of being "after the past and before the future". He also seemed to disagree with the notion that the past and future are fluid; he sees both as very much fixed. Greene discusses some interesting aspects of the time travel question. One I remember: Even if we can travel back in time, we cannot change it. We may very well have traveled back and attempted to prevent our parents from hooking up - the storyline of one well-trodden time travel paradox long-prevalent in college dormrooms - but if we did, we evidently failed, because we're here now, and that's all there is to it. We may well have been there aiming the rifle at our dad's head just before he banged our mom, but for whatever reason, the bullet didn't find its mark. Greene's works are mostly attempts to explain and popularize concepts which can only really be evaluated by fellow scientists/mathematicians. But that's what he says, as best can be recalled by this bleery insomniac: past and future are meaningless notions, because "now" is meaningless, or rather, an artifact of conciousness which has no counterpart in current science. And that the whole spacetime continuum is fixed and unchangeable. BTW, I tend to think that the problem with predicting the future lies more in chaos theory than quantum physics. But I'm no rocket scientist.
Thanks to author for this article. Very interesting. Write more!
Human intuition may know the 'answers'. We have the whole of nature's laws (at least of this Universe) encoded in every cell. The Tao Te Ching describes 'the way' as being formless yet multiform. The 'truth' is contradictory, paradoxical. Something can be and not be at the same time. This can easily be felt, but hardly reasoned out.
Isaac Isaiah (spectralmusic.com)
I agree that the past does not exist, per se, except in our memories and the results of the past on the present. So we cannot time travel back to the past. Time travel to the future is possible, however, because as we approach the speed of light time slows down for traveler. Theoretically it is possible to travel a 1000 years in the future while aging a day. You couldn't get back, however, because the past no longer exists.
But using relativistic speeds to travel to 'the future' does not take you to the future because at every single moment or instance during that journey it is the present, it just so happens that relatively your present moments are becoming your past much faster than those who are not travel at relativistic speeds. However, at the moment that you slow down to sub-relativistic speeds, you are in the present along with everyone else regardless of whether it took you 3 months to get there but took everyone else 50 years. The bottom line is you didn't travel to the future, you shifted your present out of phase with everyone else's for a while.
We can visit the future; but we cannot visit the past anymore. Do you want to visit Paris? It would take 2 hours (by plane) to get there. Do you want to visit the future, say, London in 2012? It would take a year for you to be there. You know, travels require time.
So I believe in the future(or the existence of the future); but not in the past.
question is not about; what is predictable and what is not, but actually we the human still not have that much knowledge regarding the question or same sort of issue. If we just think about our own memories, everyone has some or entire memories of even yesterday, we can even visualise it as same if we have the momories of even ten or more years ealier...so somewhere the question arises that "If there is any "space" or record room for that all past with alighty God?" just think about the JUDGEMENT DAY, how the JUDGEMENT shall happened if there's any record? It means that there is something...something to be find out by human.
if the electrons are still there and illusions arer also present then why not the past?we know that sound is energy and neither be created nor can be destroyed so as such our past illusins should exist.
Using the Hubble telescope, we can view galaxies as they existed billions of years ago. Now let us make some assumptions. Suppose our technology were vastly improved so we could observe a being on a planet in that galaxy. That being would be living in the "present" as we observed it, yet we know it was really billions of years ago. Now assume we had a second Hubble-like telescope positioned 10 light years closer to the same planet. If both telescopes took a picture of the same being, one would be 10 years younger than the other, but both would exist at the same time. Therefore, past, present, and future do indeed all exist simultaneously.
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