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Your future already exists?

  1. Jan 8, 2016 #1
    So I was watching a PBS spacetime video about... spacetime. It says that, according to relativity, your future is not only pre-determined,but it already exists. I would like someone to confirm that, because that sounds incredible. If that is a scientific fact, why isn't it more known by the public?

    Watch for about two minutes since 4:13.
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  3. Jan 8, 2016 #2


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    This program does NOT say that "your future already exists". It says that what is in your future may be in someone else's past- but that might be because that person is in your future. Would it surprise you to hear that 2020, which is in your future, a person living in 2025 would perceive as being in the past?
  4. Jan 8, 2016 #3


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    Basically, he is talking about the consequences of Special Theory of Relativity. But as HallsofIvy pointed out, the "future" and "past" has a cosmological meaning and it's not mentioned in the abstract. If you're interested, you just have to study the basics of Special Relativity to understand the Light Cone , so then what you asked will be clear.
  5. Jan 8, 2016 #4
    Oh, so it is that simple? Good. However, I'm still confused about the part he said that we, humans (as an example, of course. any object can be an example), are not moving through time from birth to death, but rather, we ARE that line. Like, a 4D object. What does he mean, exactly? Thanks
  6. Jan 8, 2016 #5
    ",,,,In physics, the world line of an object is the path of that object in 4-dimensional spacetime, tracing the history of its location in space at each instant in time. The concept of "world line" is distinguished from the concept of "orbit" or "trajectory" (such as an orbit in space or atrajectory of a truck on a road map) by the time dimension..."

    In other words, you move through space and time concurrently....
    Illustration here:
  7. Jan 8, 2016 #6


    Staff: Mentor

  8. Jan 8, 2016 #7

    Mister T

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    At 5:51 the narrator says,"And your future isn't merely predetermined, it already exists".
  9. Jan 9, 2016 #8
    What does "it already exists" mean in this context?
  10. Jan 9, 2016 #9
    Video states: "Why do we perceive reality in such a vividly spatial and temporal way? Nobody knows."

    oh,oh,oh...I know. It's because we move so slowly with respect to the speed of light our senses never prepared us for alternative extremes.

    Video says you don't move along the world line, you ARE the world line!

    I an't no stinking worldline! I'm sticking with causality and speed of light limitations.

    I just hope Peter is right: "This video appears to be reproducing a common invalid argument for the "block universe" view."

    For those interested, a bunch of pros and cons appear here w/o resolution:

    [Peter, Assume you have seen this, so many different arguments here my head spins.
    Interesting if Penrose still believes the views attributed to him. Yet as Peter pointed
    out everybody makes mistakes: I always keep in mind lots of great minds used to believe
    in 'luminiferous ether'.

  11. Jan 9, 2016 #10

    Mister T

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    It's an erroneous conclusion drawn from the fact that to some other observer their present is simultaneous to my future. That doesn't mean that my future is predetermined because, even though it's simultaneous with their present, it's also causally disconnected from it. I think it's based on a metaphysical retention of the notion of an absolute simultaneity.
  12. Jan 9, 2016 #11


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    IMHO, you may as well try to learn physics from a Tom & Jerry cartoon!

    Just after 4:13, he claims that Minkowski's idea for spacetime eradicated the notion of time! This is clearly not true at all. Spacetime represents a unification of time and space. Neither is separate and distinct from the other. But, I guess, the notion that time still exists is just too boring for some people.

    Second, if you toss a coin and then a few seconds later toss it again, then those two events take place in a given order to you. And, here's the boring bit, they take place in the same order for all other observers. No observer sees the second coin toss before the first one. This is true of your entire life in spacetime. Your path through spacetime is called "timelike" and that means that every other observer sees all the events of your life in exactly the same sequence as you do. I guess that also is just too boring for some people.

    Third, the problem with such videos (in my view) is that they try to present Relativity as a bizarre departure from what we previously perceived as reality. In fact, the opposite is nearer the truth: Relativity unified and explained the reality we already saw: the confusion was pre-Relativity, where things didn't quite add up.. The price was that we lost our notions of absolute space and time. But, in the bigger picture everything is in fact much neater and more logical. The best example, in my view, is that classical physics has three separate and distinct conservation laws: conservation of momentum, of energy and of mass. Relativity unifies those three (through the energy-momentum four-vector). But, that would go dead against the philosophy of those who make videos like this; those who want to portray physics as the weirder and wackier the better. What, physics is clearer and more logical now that we have Relativity and Spacetime? That's not at all the message these guys want to convey.
  13. Jan 9, 2016 #12

    Mister T

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    I got as far as the third paragraph, second sentence, when I ran into this phrase ...

    Immediately this introduces the notion of a cosmic "now". It is possible, you know, to form a perfectly consistent understanding of special relativity and still retain the notion of a preferred reference frame. It is a metaphysical stance, though, because there is no experiment that can detect such a preferred frame. So in this view there is still a giant clock in the sky keeping cosmic time to which all distant events can be synchronized. Such a worldview can persist within a person's mind without the person's awareness that it exists! Essentially what's happening is that the Principle of Relativity is accepted in the sense that all inertial frames are deemed equivalent, but in a purely metaphysical sense there is still one reference frame endowed with a special significance. Some people find the alternative so deeply disturbing that they cannot accept it.

    This is one reason why I prefer to say that a traveler experiences proper time in the same way as if he were not traveling, rather than to say his clock still "ticks at a rate of one second per second". I find this phrase to be not only devoid of meaning, but worse, a possible promotion of the notion of some cosmic time to which the traveler can compare his clock.
  14. Jan 9, 2016 #13
    I've been pondering this; while causality might never be violated, and everything that happens follows a causal relationship, it still implies pre-determinism IMHO.

    Tomorrow, future events will play out. We may never know what they are, but when they do happen, we will know that they are fated? :eek: Idk..
  15. Jan 9, 2016 #14

    Mister T

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    It is important to note that the implication is a matter of opinion, as opposed to being a logical implication.

    The physics does NOT imply that they are fated. It's an interpretation. It's metaphysics.
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