BRIAN GREENE: And if that’s not strange enough, the direction you move makes a difference, too. Watch what happens when the alien turns around and bikes toward Earth. The alien’s new “now slice” is angled to…toward the future, and so it includes events that won’t happen on Earth for 200 years: perhaps our friend’s great-great-great granddaughter teleporting from Paris to New York. Once we know that your now can be what I consider the past, or your now can be what I consider the future, and your now is every bit as valid as my now, then we learn that the past must be real, the future must be real. They could be your now. That means past, present, future…all equally real; they all exist.
The alien, 10 billion light years away from us, can only see our region of the universe as it was 10 billion years ago, which did not include our solar system yet. However, he could look over here, right now and legitimately say that the future of this region of the universe, for the next 10 billion years is already written. Whether or not it includes earthlings will take him another 10 billion years to find out. We are seeing the region of the universe that now presumably contains this alien as it was 10 billion years ago, and its future for the next 10 billion years has already been written. Whether or not it includes an alien will take us another 10 billion years to learn. Even if this alien, at the “present” time, hops in his spaceship and accelerates up to almost the speed of light, it will take him another 10 billion years to get here (although it could be only seconds for him) and another 10 billion years of history will have gone by during his trip, which did not yet exist at the time he started his trip. Or, if we want to consider an alien from 10 billion years ago (who we could now “see”) who would do the same thing, he would be just now arriving and during his trip, the past 10 billion years of history would have transpired in this region of the universe, as well as in his home region of the universe. (We could watch his journey and it would only take a few seconds of our time to “see” him go from his home to our home.) These comments assume, as Brian Greene does, that we are using a Frame of Reference in which an earthling or an alien is at rest. But one of the tenets of Special Relativity is that only those conclusions that are frame invariant are reflective of reality. Coordinate times and distances are frame dependent and do not comport with reality.
It’s just like in the Twin Paradox where both twins “see” time dilation in the other one’s clock and different frames will define different amounts of time dilation to the two clocks but it’s only when they return that all frames agree on the difference in time accumulated on the two clocks. Brian Greene is talking only about coordinate times on distant clocks as defined by different Frames of Reference. Of course they are going to be different but this has nothing to do with whether any future has already been written.
The Andromeda Paradox emphasises that the hyperplane called “now” is just a coordinate-based labelling of events. “Future” and “past” are meaningful only insofar as they refer to an observer’s light cones.
This, at present, is more of a philosophical question because the statement, ‘time exists’ is axiomatic with regards to physics. It seems that we need it so as to preserve causality but at the same time we don’t understand it’s presence. I like to visualize time as a membrane on which all events are allowed to flow only radially outward. A sort of heuristic boat on a lake scenario, in which the water (time) allows the boat (object) to move across the lake (space). As you go cross the lake in your boat the ripples radiate radially outward through time and space and the water isn’t being created in front of the boat as it moves across the lake, it already exists there.
Also, something sort of fun I like to think about with regard to time travel and how it is probably not possible therefore time can not be malleable.
Disclaimer: You will most likely have to read this a few times to get what I am trying to say.
Let us assume that the possibility to travel backward through time exists, then at some later time, say in 100 years from now we will actually be able to travel back in time. Also, we must stipulate that if we did travel backward in time we would be able to interact with the space at that time. And lastly, we must stipulate that time does not branch (i.e. no infinite universes theory). So, if time travel is possible then what is to say that right now is not the future’s past? That is to say that someone from the future has traveled back to now. Our present time would then be the future’s past. Because time travel is possible would mean that our present time is not the probable ‘leading edge’ of time because anyone from the future could go back to any point in time. Actually, our present time would be the least probable candidate for being the ‘leading edge’ of time (Assuming all points in time have equal “weight”).
Now since it is most probable to believe that we are existing in the past of some future time and our recorded history shows no evidence of anyone from the future traveling back in time, then their are only a couple possibilities.
Time travel is not possible, people who have traveled back in time have not been recorded into our documented history, or we are the ‘leading edge’ of time. Since there is no evidence in our historical record that someone has traveled back to then and that we are unlikely the leading edge of time, I propose that the ability to time travel is highly unlikely. Therefore time is not malleable.
Has a very distant event in our personal past and outside our personal past light cone, already happened?
Since there is no such thing as a universal simultaneousness, everyone’s personal ‘now’ cuts right through many other’s definitions of ‘past’ and ‘future’, so what exactly would a Universe look like if we’d assume the future hasn’t already happened? How would a Universal ‘now’ progress spatially if it has to deal with everyone’s definition of it?
Or, what I was referring to with the first sentence, what would a Universe look like if everyone’s past only already occurred, if it has moved within their personal past light cones? How would the Universe’s ‘coming to existence’ progress spatially, if everyone’s measurements only makes it real? When we look at the moon, all we are allowed to know is that it was there 1.3 seconds ago…
It’s at least a lot easier to think of the future as already being out there, like some four dimensional object that we live in, with the illusion of moving through it. Like Greg’s rather dogmatic explanation here.
Dr. Greene illustrated how space and time are connected by comparing the space time of the universe to a loaf of bread. Each slice of the bread was a “now” of a different section of the universe. He demonstrated how an alien on the other side of the galaxy going away from earth “now” would include our future.
Once we know that your now can be what I consider the past, or your now can be what I consider the future, and your now is every bit as valid as my now, then we learn that the past must be real, the future must be real. They could be your now. That means past, present, future…all equally real; they all exist.
Just as we think of all of space as being “out there,” we should think of all of time as being “out there” too. Everything that has ever happened or will happen, it all exists, from Leonardo da Vinci laying the final brushstroke on the Mona Lisa; to the signing of the Declaration of Independence; to your first day of school; to events that, from our perspective, are yet to happen, like the first humans landing on Mars.
Just the way an entire movie exists on celluloid, think of all moments of time as already existing too. The difference is that in the movies, a projector lights up or selects each frame as it goes by, but in the laws of physics, there is no evidence of something like a projector light that selects one moment over another. Our brains may create this impression, but in reality, what we all experience as the flow of time really may be nothing more than an illusion.
This means I’m already dead in someone else’s “now”. If the alien is traveling close to speed of light toward you, he is actually freeze in time in your time frame, you’ll be progressing until you are dead in normal speed, then the alien will wake up and find you dead.
Me: I heard Jamal from 90th street watched that tape last week and this mornin’ he woke up dead!
You: How the hell do you wake up dead?
Me: Cause’ you’re alive when you go to sleep.
You: So you’re telling me you can go to bed dead and wake up alive?
Me: You can’t go to bed dead! That shit would’ve been redundant.
You: No it would’nt cause’ you can go to bed and not be dead, and you can die and not be in the bed.
Me: But you are in the bed. That’s how you wake up dead in the first place fool!
You: Damn! that’s some quantum shit right there man! You should be teaching classes!