Time travel

God... you make so much sense with so few words. I'm jealous.

And even if you could revert all particles of the universe to a prior state, you didn't even manage to travel back in time then. You have just made it the second time that such a state has occurred. The first time that state occurred, it was distinguishable from the fact that it had never occurred before. The two states are still unique in this way.

And the probabilistic nature of matter would keep that second state from behaving like the first one anyway.

 

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I find this all fascinating, and yes I will find a bigger sci-fi fan then you, me! LOL

So you're trying to say the concepts physicists mention are all merely equations without any real substance in the world. It could be that way, however I also am not certain it is...

If the universe is just a state, an each change in that state is called Time, well... there must of a dimension upon which this states action follows. If there is then wouldn't traveling along this dimension allow us to go back to a previous state the system was in?

 

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Next time you're cruising by M-87's 4.5 billion solar mass Supermassive Black Hole, check your watch. It might be a little slow.

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a lot of people are saying that time is a concept and can not be slowed down or sped up, and i hate to tell you but you are dead wrong. Time can be measurably slowd down due to acceleration or strong gravity. That is a fact, it has been measured. An to say that teh devices we measure time with are slowed down but "time itself" is not is absurd, for how else do u define time otehr than by clocks. time dilation is measured not only by clocks but all time processes, such as aging or radioactive decay. get your facts right; time is relative, it can be slowed down or sped up; the only thing in the universe that is constant is teh speed of light. And yes, it is a fact that time dilation can be used to visit the future. By travelling fast enough, you could age a short amount of time (measured by your watch or how much your beard grows) but a huge amount of time would have passed for everyone else. You could get to teh year 3000 in a few minutes.

 

I don't think any of us that are saying time travel is impossible have ever stated that it was constant from all perspectives. Most people struggle with the concept of time, without me confusing them with how gravity and acceleration alter the relative flow of time.

And changing the relative rate at which two people age is not travelling to the future any more than the people left on Earth, undergoing a different rate, can be said to travel into the future while the spaceman is off on his voyage. Again, too many sci-fi books are clouding everyones understanding of the most basic concept of what time is.

 

no, the people on earth are not travelling to the future, beacuse they only experience teh years of their lives (0-100something years max) many generations have died when the spaceman returns. he who can see and visit the year 3000 has manipulated time. You are the one who seems mistaken about time. what exaclty is the "nature" of time to you? is time moving straight ahead, with the past gone and the future not yet to come? that view is plain and simple wrong, Einstein's theory of Relativity disproves this rigid division of time. the words "now" or "then" or "in the future" are meaningless because they are differnt for everyone. Try to widen your own perspective of time, instead of viewing it as a rigidly divided arrow.

 

Hrmmm... I'd be very leery of anyone who claims fundamental understanding of what time is. The debate over presentism vs eternalism is unresolved, and perhaps unresolvable.

You may certainly be correct, but it certainly isn't certain

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I think that our limited grammar might be trapping you.

Time travel wouldn't mean that the past exists now... that's absurd. It would mean that for two coexistent entities A and B, the future of an entity A may coincide with the past of entity B.

How you describe this grammatically is a problem... The main work to consult in this matter is Dr. Dan Streetmentioner's Time Traveler's Handbook of 1001 Tense Formations.

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In practice, I believe that as a matter of convenience.
But strictly speaking it is an act of faith, not rationality.

 

There have been some interesting articles published on the issue of the nature of time recently in Analysis (Blackwell Publishing).

The full text is subscription only (although there are some free sample issues including January 2006), but some abstracts are available. I also found a preprint of How do we know it is now now?, which has some fascinating things to say about philosophies of time, eg:

What do other theories of time tell us about how we know that the current time really is the present? If you are a presentist then the genuine passage of time poses no epistemic problems. For according to the presentist all that exists is the present, so the fact that we know we exist guarantees that we are in the present. The presentist has an objectively characterized conception of the present, but it is one we have simple epistemic access to. If you are a four dimensionalist, it is equally easy to say why we know the current moment of time is the present. For most four dimensionalists have an indexical conception of ‘now’. ‘Now’ just means the moment at which it is thought or uttered. So people at any location in spacetime who believe that they exist in the present, will believe correctly. There is a little more to be said about the present in such a model:
the indexical element tells you only that at each location in spacetime the present is a hyperplane of simultaneity that includes that location, but it underdetermines which hyperplane that is. A further relativization to a frame of reference is required, but that does not add any substantial difficulty.​

(Braddon-Mitchell, David 2004, How do we know it is now now? Analysis 64 (283), 199-203.)

It inspired some follow-up articles which I can't access but look as though they provide significantly different viewpoints.
Here

Here's an abstract of one (David Zimmerman, The A-Theory of Time, The B-Theory of Time, and 'Taking Tense Seriously'):

The paper has two parts: First, I describe a relatively popular thesis in the philosophy of propositional attitudes, worthy of the name 'taking tense seriously'; and I distinguish it from a family of views in the metaphysics of time, namely, the A-theories (or what are sometimes called 'tensed theories of time'). Once the distinction is in focus, a skeptical worry arises. Some A-theorists maintain that the difference between past, present, and future, is to be drawn in terms of what exists: growing-block theorists eschew ontological commitment to future entities; presentists, to future and past entities. Others think of themselves as A-theorists but exclude no past or future things from their ontology. The metaphysical skeptic suspects that their attempt to articulate an 'eternalist' version of the A-theory collapses into merely 'taking tense seriously'– a thesis that does not imply the A-theory. The second half of the paper is the search for a stable eternalist A-theory. It includes discussion of temporary intrinsics, temporal parts, and truth.​

I don't pretend to fully comprehend the discussions

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Pete, here is an Aug. 15, 2006 draft of a new paper by Dean Zimmerman if you are interested. I haven't read it yet as it is 47 pages long.
"The Privileged Present: Defending An A-Theory Of Time":
http://fas-philosophy.rutgers.edu/zimmerman/PrivilegedPresent.pdf

 

Thanks 2inq.

 

So, you are saying that since someone is undergoing a flow of time at a different rate, they are "time travelling" (I'm thinking about the astronaut travelling at relatavistic speeds).

That would mean that someone living in Denver is "time travelling" compared to someone living in Miami, right? And the people in airplanes are "time travelling" even more. And the current occupants of the ISS are "time travelling" even more.

This is the logical extension of your example, and it leads to silly stuff. Just because a guy is able to preserve his cells, by making them age slower, in relation to other people's cells, does not "time travel" make. If that were true, then all Denver residents are "time travelling".

Again, you are not discussing the nature of time, you are playing with the sci-fi potentials of relativity. No harm there, I do the same thing all the time. I love thinking about "skipping" through time like a relativistic stone. But that isn't time travel, it is cellular preservation thanks to some effects of relativity.

Again, none of us that have insisted that time travel is impossible have EVER SAID, NEVER, NEVER, NEVER, NEVER, that time flows steadily, or that we have a rigid concept of time. NEVER, NEVER, NEVER. So, please stop erecting Straw Men and putting words in my mouth. It is rude and intellectually dishonest. We can talk about the relativistic properties of time-flow if you want, but it just isn't germane to this thread. This thread is about time travel, which is a myth.

Cheers.

 

I got through most of it. A great find, and a very fascinating read!
Zimmerman seems very well informed, intelligent, articulate, honest, and forthright. I'll look up more of his work, and follow up his more interesting references.

I'm not convinced of his conclusions, but he has certainly raised my awareness of and sympathy for the presentist philosophy of temporal reality.

Some portions were a bit too deep to comprehend fully. I'll read it again in a few months or a year, and see what more I can get out of it.

Thanks again

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It is an interesting read, mainly to see the flaws in most theories of time, especially philosophers.

When people critique the Presentist point of view, they make the mistake of equating the claim that the past "doesn't exist" with the claim that it "didn't exist". I don't know any Presentist who would argue that the past was not a one-time, and very real, Present. Or that thinks there will be more "Presents" to come.


Also, a common mind-twister that gets people all riled up is the idea that all things occur in the past, because by the time we are aware of them, they are already gone. This is the infintismal conumdrum that haunts most conceptualizations of time. It takes time for the light of an event to travel to our eyes, and register in our brains, therefore our perception of things is how they were in the past, not how they are now.

All of this reasoning is missing the point, and silly. If you are talking about Time from the perspective of Human Perception, you are bound by the realities of Human Perception. When we sense things has no bearing on reality. That is the sort of egotistical reasoning that gets philosophers into so much trouble.

Let's create a simple model so we can see what really happens. We have a tree with some apples in it (which, I suppose, will mean that it is an Apple tree). We also have two observers. One observer is right beside the tree, another is a mile away, looking at the tree with binoculars (bird watching we may suppose).

An apple falls from the tree. The person near the tree sees it falling as does the person with the binolculars. Let's explore the reality of any given moment, like... half-way down.

When the apple is IN REALITY, halfway to the ground, the person near the tree will be perceiving it as being just a tiny, tiny, tiny bit higher than that. It is taking time for the light to enter his retina, and be processed. The person with the binoculars is seeing the apple a tine, tiny, tiny bit higher up from the other person. And ALL OF THIS IS REALITY.

The STATE OF OUR SYSTEM includes the apple, and where it is. PLUS, the observers, and the state of their brains, and where it tells them the apple is. Also a part of any state of the system is a gradual ray of light, carrying a reflected image of the apple in various positions as it falls. All of these things are part of the objective reality. The simple fact that the perception of some human observers LAGS behind that of the reality, does not mean that humans live in the past. It just means that in any present, humans are only capable of PERCEIVING the past. This only makes sense, it takes some TIME to PERCEIVE.

None of the perceptions changes the location of the apple, which has a definite place in every state of the system. And what the state of the brains of a meaningless organism is at any time does not change anything. That is like another posters comment that slowing down the aging of that organism means that the organism is travelling through time. It is an egotistical and self-centric way of looking at reality that trips up philosophers and amature alike.



I can't tell how much I am assuming here, and how much I am overly-spelling things out. If this does or does not make sense to the reader, I would appreciate some feedback. It is hard to tell otherwise if I am coming across like I am talking down to people (which is rude), or like I am talking over people's heads (which is rude). I am just not very good at communicating in this medium, I much prefer face-to-face conversations so a head-nod, or a puzzled look can give me the feedback that prevents these two errors.

 

You're spelling out your position well, I think.

The reason that I personally balk at presentism is the relativity of simultaneity.

Consider some event happening now in the Andromeda galaxy...
If I get up and walk in the general direction away from that galaxy, then suddenly (!) that event is perhaps a day in the future. If I reverse my perambulation, then now the event is a day in the past...

What's going on? What is the status of that event in reality?

 

First off... you are a fast walker.

Secondly, you are again confusing perception with reality. These are two different conversations.

Edit: I just can't be brief, no matter how hard I try. The problem with your scenario (which is accurate, I don't dispute that), is that the reality of any moment is dependent on features such as relative motion. That doesn't mean that two different things can happen at once. You either have to choose to walk away from Andromeda, and be a part of that reality, or you have to choose to walk towards it. The fact that both are potential realities never means that both could simultaneously exist. See what I mean?

 

Nope

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work it out!

I think not. Time dilation and simultaneity have nothing to do with when an observer perceives an event, but rather they are about when said event occurs. In the case of events at Andromeda happening now, I'll never perceive them.

 

I was joking.

The point of my post is that you can't have it both ways. The relativness of when something happens doesn't mean that there isn't a singular "now". If you look at this dot ---> . The moment you look at it, the matter in the universe, and all the energy has a particular distribution. Even with Heisenburg's Uncertainty Principle, and Bell's Theorem. Even considering Quantum Tunneling, and the probabalistic distribution of electrons in an atom's cloud. At any time that you look at that dot, the universe has a state. Since this state can change, and does, we have time. Just because the universe is expanding so fast, that RELATIVE to the Andromeda galaxy, we are moving fast enough for Time to have relativistic properties does not change this fact.

Walk one way, and the state of the universe is one particular way, walk the other way, and it still obeys the realities of physics, and you have another state.

And of course you are talking about PERCEPTION when you say that something in another galaxy is occuring "Today", "Yesterday", or "Tomorrow". Those comments only make sense in the framework of human perception. You are confusing our standards for measuring time with the concept of time. From the basic concept of time, it doesn't make sense to say that "if I walk this way it happens tomorrow, if I walk the other way it happens yesterday", those are concepts that require perception and our man-made units of time. Without perception, that example doesn't make any sense. Our fictional dude can't look at his watch, or know which direction to walk.

And yeah, I read the same book that the exact scenario you mention occured in, and he also used the Andromeda Galaxy as his example. A link and some credit would be great. I can't remember if it was Greene's "Fabric of the Cosmos" or Coveney's "Arrow of Time". It has been over a year since I read it. I remember, even then, realizing that this brilliant author was confused, and hate to see that his confusion was spread along with the other more intelligent things he had to say.

 

That's not what special relativity says. It says that "the moment you look at it" has a different meaning depending on ones state of motion.

The Milky Way and Andromeda are approaching each other at about 300km/s, or 0.001c - a gamma factor of only 1.0000005.

What I said before still stands. SR makes specific predictions about the order in which events occur, and changing reference frame by a very small velocity has a large impact on the order of events at large distances.

And the difference between those two states is that many events which lie in the past of the first state lie in the future of the second state.

I don't think so. To consider the temporal relationship between events A and B is integral to the concept of past, present, and future. To suggest that one is dependent on human perception is to imply that the other is as well.

Perhaps... but that's not the essence of what I said.
Would you agree that saying "A occured before B" makes sense in the basic concept of time?

Also, I'm not convinced that you have a handle on the relativity of simultaneity. Please forgive me if I'm incorrect

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I forgive you.

 

In case you didnt notice, i was not talking about just you. You understand that time is not rigid and can be manipulated, making everyone, in a certain sense, a time traveller. However, there are other people here who refuse to believe that such as this quote from c7ityi

"time is a concept arising from change and motion, and therefore from the succession of cause and effect. you can't seriously think that time is a physical reality. time (and space) supposedly bends in gravity, but how's that possible since time is not made of anything? time is mental, that's why it can only be affected by our state of consciousness (ex: happiness, sadness)

'time itself' can't slow down in gravity or affected by acceleration, the instruments we measure time can be affected however. "

this person does not believe that time can be affected by gravity or acceleration; he is the person i was saying was wrong. Sorry for the confusion.

Yes, i agree that this sort of "time travel" to teh future is not really time travel in the usual meaning, however, there are many theories for actual time travel to the past which have not been disproven and do not break any laws of physics. How can you be so certain that time travel is a myth? I am not claiming it is possible, i a merely claiming that we dont know and havent proved it impossible yet. What i find rude is how you speak with such absolute certainty on things you dont and cant posssibly know everything about.
**Unless you're some sort of omnipotent god or soemthing of that nature, in that case, i apologize.