Time travelogue

Posted: Wednesday, May 20, 2009 8:26 PM by Alan Boyle

Warner Bros. Pictures

Can time travel save Los Angeles? Marcus Wright (played by Sam Worthington)
surveys post-Judgment Day destruction in the movie "Terminator Salvation."

Time travel has been a standard feature of science fiction, but never more so than today: The latest "Star Trek" and "Terminator" movies, as well as the TV series "Lost" and "Heroes," play off the classic paradoxes, and still more shows are on the way. In fiction, all it takes to travel back in time is a black hole or a flash of energy, with nothing more than a hand-waving explanation. If only real-life experiments in time and causality were that simple ...

It's easy to get your mind tied in a knot if you think too much about moving through loops of time - the sort of thing that inspires Heinlein short stories, "Twilight Zone" episodes, "Back to the Future" sequels and "Simpsons" parodies. To make things simple, let's just accept the first item in Cosmic Variance's Rules for Time Travelers: that there are no paradoxes.

This leads to three main conceptual avenues for time-travel plots:

"Whatever happened, happened": The past can't be changed, even if you could try. Something would keep you from preventing Abraham Lincoln's assassination, and you might even end up helping John Wilkes Booth if you interfere. Famed physicist Stephen Hawking sides with this view, calling it the "chronology protection conjecture." And I suppose that, by implication, the future must take its course even if you could manage to foresee it. This is the approach suggested by "Lost," although there are hints that things may change next season.
Many-worlds interpretation: This is the favorite way for Hollywood to do time travel. Why travel at all unless it makes a difference? But what happens to the chain of causality if you make a change - for example, killing your father before you were born? The many-worlds interpretation of quantum physics comes to the rescue, by suggesting there are a nearly infinite number of possible universes branching out from each moment. You can either stay in the changed past, or go back to the original or a different future. (But how do you choose? Maybe "The Simpsons" had it right after all.)
"Change these shadows": The third possibility applies to visions of the future or the past, rather than actual travel back and forth in time. One of the practitioners of this concept was Charles Dickens, who provided a loophole for Scrooge when the Ghost of Christmas Yet to Come showed the old humbug his possible future. "Assure me that I may yet change these shadows," Scrooge pleaded. Such visions may turn out to be alterable or just plain wrong. This is the sort of thing you see in TV shows like "Life on Mars" and "Medium" - and "Dallas," for that matter.

We have a limited ability to anticipate and change the future, of course, but is it at all possible to change the past? In a sense, that's what University of Washington physicist John Cramer has been looking into.

For more than two years, he's been trying to set up an experiment that would test a phenomenon suggested by quantum mechanics: If you change the quantum state for one of two entangled photons, it might be possible to have that change reflected in photon No. 2 before you make the change in photon No. 1. The implications of the experiment are so intriguing that Cramer's fans contributed more than $35,000 to keep it going.

I've checked in with Cramer in 2007 and 2008 (twice!) to find out about his progress, and the latest is that the lab apparatus is still not right to do the experiment. The crystals that he originally planned to use have a "huge signal-to-noise problem," he told me today. The few entangled photons produced by the crystals are overwhelmed by stray photons that muck up the detection effort.

"Phase 1 and phase 2 [of the experiment] hit the wall, and we're about to start phase 3," Cramer said.

To get around the problem, Cramer is planning to switch to periodically poled crystals, which he said fellow quantum researcher Anton Zeilinger has used to produce millions of entangled photon pairs per second. Cramer still thinks his experiment is a "long shot," however. He suspects some factor will always prevent him from observing retrocausality in action.

For example, there appears to be a complementarity between quantum coherence and entanglement, he said. The more certain you are that the photons are really entangled, the less certain you are about the photons' quantum coherence. Both factors need to be nailed down in order to verify that retrocausality really, really works. "That could be the showstopper," Cramer said.

Until Cramer actually sets up the experiment with the new, improved crystals, he'll never know. But even if the experiment fails, it won't be a total loss. Because Cramer is a columnist and novelist as well as a physicist, that will just give him something to write about in his next book. Who knows? Retrocausality may soon be coming to a bookstore near you - or at least an alternate universe near you.

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Comments

If ya open a magically sealed container of air from pre-history for the first time and breathe it in, wouldn't that be time travel?
The olfactory sensations would stimulate every Aboriginal Memory.
Or, to make things easier, how about recalling the scent of anything from before...Mom's apple pie...it always brings one right back to that time, eh?
Wonder just how far back memory can go with proper stimulus...hmmm!!!

steve smyth (Sent Wednesday, May 20, 2009 9:21 PM)

I disagree, there is no concept of time without change, and no concept of change without recordings. And some recordings can be changed. Usually your own recordings. Some times even many other related recordings. This is by definition an artificial change of the past. In a few decades if we preserve our memories we should be able to travel in our own past and maybe even explore what if scenarios of past decisions. We might be able to change our recordings, pretty much the same way we try to erase ugly memories now...

Steve Ianta (Sent Wednesday, May 20, 2009 9:36 PM)

crazy i hope it works cause i would really like to eat tht last piece of pizza before it molds in my fridge.

bob (Sent Wednesday, May 20, 2009 10:10 PM)

Consider this: there's been lots of hypotheses about how going back into the past would change the present and/or future. But what about simply viewing the past? Oral historians often mention the magnifying effect that the passage of time has on embellishing past persons or events; this is how they become larger-than-life by the act of re-telling over time. What would happen to our world view if we could go back to observe the life (and death) of Jesus? And if you're brave enough to view that, would you also be brave enough to go back and re-visit your own adolescence? Ans what about the issue of privacy if anthing and anyone was viewable? "The Light of Other Days" by Arthur C. Clarke explores this better than anything else I've ever read!

Ron Martin (Sent Wednesday, May 20, 2009 10:59 PM)

I see a problem...if Cramer can step through time, no one will notice any changes (except Cramer of course) because everything will just feel like thats always how it has been. Maybe someone has already travelled through time, but does not announce it and changed several things to make the world what it is today..Perhaps McCain actually faced Hillary in the last election and won, but a time traveller saw bad consequences. He fueled Obama from birth and helped him into the presidency. All the rest of us, now know nothing of an Obamaless America. (Note:This change also gave California its movie star Governer by allowing him to move to America much sooner and thus become eligible. The Terminator movies fueled the time travellers theory and sought to honor it.

Michael, Quebradillas Puerto Rico (Sent Wednesday, May 20, 2009 11:03 PM)

Cramer will never reach retrocasuality until he polarizes the quark through Impulsed electromagnetized photon energy at the same MEV of the crystals. The catalyst being the chemical composition and radioactive emission of the chemical imbalance to the polarization and the electromagnetic frequency wave form of the crystal photon energy emission. Control of the MEV emission is necessary to counter the photon polarization thereby defining the quantum coherance for individual pair separation. I'm sorry to say at the present and past failures of Cramer's experiments, he is also failing to realize the quantum paralax of fifth, sixth and even seventh dimension universes. Both time and space will have to be bent quantumly to reach the continuum of spacial differential to move past the time barrier. The main problem is in the photon to quark differential, and separating the positron pairs is negative to the time relativity of the sequential pairing.

Bill Ribbing (Sent Wednesday, May 20, 2009 11:58 PM)

When the universe stops expanding and then contracts, will time then go in reverse?

Bernard Tormey (Sent Thursday, May 21, 2009 12:50 AM)

Who knows, maybe Einstein read H G. Wells' "The Time Machine", circa 1895, as a youth.
http://en.wikipedia.org/wiki/The_Time_Machine

Obviously Wells had something...and so did Einstein.

Thomas Ashby, Calgary (Sent Thursday, May 21, 2009 1:06 AM)

"Cramer will never reach retrocasuality until he polarizes the quark through Impulsed electromagnetized photon energy at the same MEV of the crystals. The catalyst being the chemical composition and radioactive emission of the chemical imbalance to the polarization and the electromagnetic frequency wave form of the crystal photon energy emission. Control of the MEV emission is necessary to counter the photon polarization thereby defining the quantum coherance for individual pair separation. I'm sorry to say at the present and past failures of Cramer's experiments, he is also failing to realize the quantum paralax of fifth, sixth and even seventh dimension universes. Both time and space will have to be bent quantumly to reach the continuum of spacial differential to move past the time barrier. The main problem is in the photon to quark differential, and separating the positron pairs is negative to the time relativity of the sequential pairing."

Dang, I was going to say that!!

Sapphia, Seattle, WA (Sent Thursday, May 21, 2009 1:16 AM)

A proton walks into a bar, bartender asks if he was sure he was in the right place. The proton says, "I'm positive!"

Sapphia, Seattle, WA (Sent Thursday, May 21, 2009 1:18 AM)

I must disagree with Ribbing's comment regarding the polarization of the quark. A pre-existing sub polarization of the quark matrix has always been considered to be sufficient for quantum coherence in a trilateral state. futhermore, the concept of bending time and space is simply ludicrous as we all know time to be circular and therefore same space loop causality will ensure the future of time travel experiments and the possibility of time travel itself. Perhaps if bill were to read a little more on the subject he could put a comment down that does not read like something out of a L. Ron Hubbard novel. Photon quark differential indeed. good day to you sir.

Dr. John Montgommery (Sent Thursday, May 21, 2009 2:52 AM)

Bill; I find flaws in your reasoning.

Striker,rome,NY (Sent Thursday, May 21, 2009 4:51 AM)

Maybe its just my limited knowledge of physics, but isnt part of the whole concept behind quantum mechanics that we cannot actually measure or "see" the location/state of sub atomic particles because any attempt to view/locate/measure them would alter them. And so quantum physics is a way around this problem to provide data on the very small. If so, how could any experiment in retoactive causality on sub atomic particles actually prove anything, when we dont really "know" the exact state of what we are trying to measure/view/locate?

Greg, NJ (Sent Thursday, May 21, 2009 7:35 AM)

Life, (Time for that matter) is a butterflys dream, dreamt on a war summer day.

There is no past, there is no future, there is only now, the moment you are in as you read these words.

The so-called past is altered everday by historians, politicians and the fallibility of human memory to suit our own petty purposes.

The future is a promise that is rarely kept.

If you want to look to the past look deeply into the night sky and the light of stars traveling millions of years to twinkle over the earth.

If you want to look to the future look at your children and remember they are the future and that future is yours to shape.

W.A. Nicholson, Oklahoma City, OK (Sent Thursday, May 21, 2009 8:33 AM)

It was all so neatly packaged by Groucho Marx's quip:
"Time flies like an arrow. Fruit flies like a banana".

Steofan M., Bozeman, MT (Sent Thursday, May 21, 2009 9:13 AM)

Ladies and Gentlemen with all the let's say very, very, very advance accomplishments in technology today it's very possible time travel not far away. Besides Cramer can experiment all he wants, until the speed of light is harnish there will be no time travel. I know he's on the wrong track, but good effort and trial.

Captain Duke the Arn Dike (Sent Thursday, May 21, 2009 9:48 AM)

Interesting article Alan! Time travel sure brings up lots of conjecture about changing the past and its effects.

I think that John Cramer is chasing his proverbial tail around on his experiment to see if one photon of an entangled pair of photons can change before its paired twin gets changed. I think the retrocausality concept is bogus because the first photon that changes is the one that is supposed to change and the second changes in response to the first changing, not the other way around. Either that or a mistake was made in assuming a certain pair of photons were truly entangled in the first place. It will be interesting to hear further on this experiment as Cramer gets his new one set up and running.

Eric, Salinas, CA (Sent Thursday, May 21, 2009 10:45 AM)

Alan, I've been wondering this for a while now. How do you move an object back in time without it immediately colliding with the previous instance of itself? Wouldn't you also need to achieve an instantaneous physical translation in space of a distance larger than the object's radius to prevent all its particles from ramming into themselves a femtosecond (or less) earlier in time? I wouldn't want to be anywhere near the resulting explosion... But of course, that too would be one of those grandfather paradoxes: the object would be destroying itself and its surroundings a tiny moment before you attempted to send it back in time. :)

Stowe, Charlottesville, VA (Sent Thursday, May 21, 2009 11:14 AM)

The past is the past - so, if anyone was going to manage to travel backward in time, then their arrival there has already happened. Thus, the results of any actions taken in the past by a time-traveller from the future are already reflected in the present. So if you could travel to the past, you couldn't change the present (or the future) because you were already IN the past - you arrived at your destination before you began your journey... oh dear, I've gone cross-eyed.

DL, DSM, IA (Sent Thursday, May 21, 2009 11:18 AM)

I don't think travel into the past would be possible. If, as is theorized by quantum physics that events are perceived and the wave function collases one of many possible states, one (large) wave function describes the universe, then one would have to uncollapse that wavefunction for the whole universe, which would take infinite energy and is therefore not possible.

Rick S. (Sent Thursday, May 21, 2009 11:21 AM)

I am an avid Lost viewer, but I disagree with the "Whatever happened, happened" theory. The present is arbitrary, depending on the participant; and one man's present is another man's past and yet another man's future. If "whatever happened, happened" is correct, then we would live in a singular, completely deterministic reality. Not only is the past determined, but the future is determined as well (since it is the past for some). A more thorough description of the "whatever happened, happened" theory would be "whatever will happen has already happened." I would conclude that we live in a multi-verse or that time travel is not possible. Otherwise, free will is an illusion; and so is the uncertainty principle!

SD, Worcester, MA (Sent Thursday, May 21, 2009 12:15 PM)

"the concept of bending time and space is simply ludicrous as we all know time to be circular"
-----
You've got a funny definition of "all", Dr. John.

Ray B., NYC (Sent Thursday, May 21, 2009 12:40 PM)

To travel back in time would'nt you also have to travel back in space? If I were to go back 1000 years the earth would still be 1000 years away from this part of the universe. Only some faster than light energy would be able to travel out in space and zoom in on the past. The carousel theory is interesting but not too likely.

Carl, Orange, CA (Sent Thursday, May 21, 2009 1:01 PM)

Wasn't it Einstine who said that if you place a man in a box and move the box up down left or right at a constant speed then he would never know if he was moving? So if said man had no feelings of hunger, sleep, or history of past would he still feel as if he were traveling through time? This question is asked all based on the notion that we are all traveling through time at the moment(in reality we are forever moving forward in our own minds). In my own thoughts I would have to say that time is a variable. There really isn't any true law of time, its just distance*speed. Think of it as a ray of light. One thing is for sure, you can always bend light but you can never make it go backwards. But with bending it i'm sure you could make it go faster. So by that theory one can travel further into the future, but never go any slower than it already travels. maybe i'm rambling, i'm just a geek with a dream.

Geekery, J (Sent Thursday, May 21, 2009 2:17 PM)

If you traveled to the past than the past would now be the present, could you therefore see the future? The future is after all that which has not yet occurred.

Tony Rotz (Sent Thursday, May 21, 2009 3:30 PM)

If Cramer's experiment is undone by noise, it would be interesting to find the source of that noise. The GEO600 experiment near Hanover, Germany was set up to look for gravitational waves, but has been plagued with a strange inexplicable noise that Fermilab scientist Craig Hogan suggests may be evidence of a resolution limit in a holographic universe (New Scientist No. 2691.) The noise that is obscuring Cramer's experiment may be topologically similar, except across the time dimension. In effect, it may represent, in effect, a limit of resolution in our analysis of causation.

By the way, Alan, congratulations on your new book! And, I assume the Heinlein time-travel story you're referring to is "Blowups Happen?"

[ALAN ADDS: Thanks, Richard: Prof. Cramer actually told me about that GEO600 issue some time ago but I wasn't able to follow up on it before New Scientist's story came out. Thanks also for the congrats on the book (I hope you'll give it a look). Actually, the Heinlein story I have in mind is "All You Zombies."]

Richard Miller, The Woodlands TX (Sent Thursday, May 21, 2009 3:42 PM)

Let's say there is a point 1 light-year away and a red electric bulb at that point is switch on. The observer receives the light (watches the event) one year after it is switched on. If he wishes to receive the red light again (watch the same event happening), he needs to travel faster than light and position himself in front of the rays (spreading out in a sphere). My take is that we cannot go into the past nor change it.

Rakesh Sharma (Sent Thursday, May 21, 2009 5:05 PM)

One problem with time travel, if it actually moves something to the same physical location, but at a different time, is that the target location won't be there! The Earth moves, the Sun moves, the galaxy moves. If you went to the same location a day earlier, the Earth would be somewhere else, unless your machine also accounts for all of the spatial motions.

If you can find a novel by Kames White titled "Tomorrow is Too Far" he comes up with some strange consequences of this, as well as a means of using it for space travel, but with serious side effects.

N Kalanaga, Grayson, KY (Sent Thursday, May 21, 2009 5:10 PM)

Of course time travels at the speed of light. How absurd it would be to say that light at its fixed speed actually travels into the future by exceeding the speed
of time! I believe that time and light are the same, in
the sense that they determine the spatial framework that we exist in.

And, please people, don't cheapen your arguments with
references to 'science' fiction.

Mr. Isenglasse, Salem, OR (Sent Thursday, May 21, 2009 9:14 PM)

Couldnt the noise in his experiment be the result of all the other parrallel universe Cramers attempting the same experiment at the same "time" thus by trying to... touch the past I guess you would say he is in fact causing his own experiment to fail. I see the universe/time space all that mess in the fashion of the quantumn multiple universe. The only way to succesfully then to complete this experiment would to be to find some way to seperate your own experiment from all of the others happening at the same time... alright hurting my head but hopefully that suggestion makes some sense

S. Harrelson, Mt Airy, NC (Sent Friday, May 22, 2009 12:59 AM)

One of the major problems encountered in time travel is not that of becoming your own father or mother. There is no problem in becoming your own father or mother that a broad-minded and well-adjusted family can't cope with. There is no problem with changing the course of history—the course of history does not change because it all fits together like a jigsaw. All the important changes have happened before the things they were supposed to change and it all sorts itself out in the end.

The major problem is simply one of grammar. For instance, how to describe something that was about to happen to you in the past before you avoided it by time-jumping forward two days in order to avoid it. The event will be descibed differently according to whether you are talking about it from the standpoint of your own natural time, from a time in the further future, or a time in the further past and is futher complicated by the possibility of conducting conversations while you are actually traveling from one time to another with the intention of becoming your own mother or father.

Tony, Dallas, Texas (Sent Friday, May 22, 2009 10:51 AM)

Although it may one day prove possible to go forward in time (by removing something from space time then re-introducing it back in at a later time), going back in time is highly unlikely.

For one thing, space and time may be different aspects of the same thing and time is relative (only meaningful and relevant to the observer).

The faster you move, the slower time flows for you. The slower you move, the faster time flows for you. Stop all movement (energy) within an object and you remove it from space/time (and would be unable to observe it as it would not affect its surroundings in any way making it effectively invisible to you).

The universe is expanding quite rapidly. If you were able to send something back in time, it would not appear on Earth as the Earth is moving. You would have to be able to modify not only time, but space as well.

Which means that in order to have time travel, you'd also have to have teleportation (for lack of a better word).

Jerry of Madison, WI (Sent Friday, May 22, 2009 11:36 AM)

"Of course time travels at the speed of light."
Time doesn't travel, time is travelled. Time is an aspect of space/time, the two are entwined and it is generally agreed that you can't talk about one without the other. Just being able to travel time is meaningless, you would need to travel space/time to actually get anywhere.

For another good Heinlein story about cause/effect and the futility of changing the past, try "By His Bootstraps". By far my favorite, but "All You Zombies" takes a close second place.

Scooter, Pittsburgh PA (Sent Friday, May 22, 2009 11:43 AM)

Netsrik, SLC, UT (Sent Friday, May 22, 2009 4:30 PM)

I will have pizza for lunch yesterday, because I had eggplant tomorrow, and I need some variety. After tha I'll be going to last week, to try to solve next month's communications problem.

English works just fine for time travel, as long as you consider past and future as locations, the same as geography!

N Kalanaga, Grayson, KY (Sent Friday, May 22, 2009 5:12 PM)

An instant in time, delta-t = 0, presumably can be described by specifying the quantum states of each and every "particle" in the universe. Going back in time is simple: recreate the universe with those previous quantum states...each and every one being identical to those that previously existed. Without doing this, you are not in the same place/time that previously existed.

{DvT}Hex (Sent Friday, May 22, 2009 7:37 PM)

I don't know here you came up with time being circular, since time is infinite and unmeasurable to it's beginning and end. Going back in time would require bending time back upon itself which is impossible in infinity, however I agree that light is bent with time but photon emissivity follows the rules of time and can't be bent back upon itself. Your reference to circular time is another unproven theory since time is a constant forward progression. Let the world know when you stop time!

Just an observer (Sent Saturday, May 23, 2009 4:30 AM)

Change happens; time does not; that is until consciousness (humans) enter the picture. Time is a CONCEPT; man's attempt to measure change. I hope we're not spending too much trying to unmeasure change, nor to measure unchange; whatever that is.

Hank Cole (Sent Saturday, May 23, 2009 9:08 PM)

I'm not a scientist, but I think they are missing the point:The laws of thermodynamics rule time.

You can't have a future event without a constructed past. any action like flicking a finger requires gauge forces which move the trillions of quarks in that finger. I've read there are as many quarks in a finger as stars in our galaxy. I always wondered how can they all move? Then I remembered in an electrical circuit it's not an individual electron that travels from + to - but rather electrons jump to "holes" which bump other electrons etc until AN electron reaches the positive end.I think the same thing happens with quarks the "multiple" universes is actually the quarks hopping (somehow) and allowing that finger flick.

The bottom line is a future can't exist without a past - it is in effect result of all past events.

Luis M (Sent Saturday, May 23, 2009 11:18 PM)

i like the idea of many worlds, because somehow, somewhere i rule the world. i just have to figure out how this presence of mind (the one writing this comment) and all presence of my mind in other worlds be in that world. ahhh, such bliss...

Eddie Q., Redlands, California (Sent Sunday, May 24, 2009 1:37 PM)

Does a black hole also suck in space/time along with everything else in c lu di n g

Q (Sent Sunday, May 24, 2009 1:59 PM)

I hear a lot of people suggest time's nature is photonic, But that arises from quantum theory - there is another interpretation more based on fact - Time's nature is gravitonic. It has been strongly theorized that time slows in the presence of gravity, and until now the graviton the theorized force carrier is not photonic. It is a "wish" of many grand unified theorists that gravity, the electromagnetic, and electroweak forces are united in one grand unified force.

Time is the spoiler: Time is unique in that the inverse of time is frequency how is frequency affected by gravity or space or in a black hole?

Luis m (Sent Sunday, May 24, 2009 11:00 PM)

In Oxford England there are 3 scientists who have a real time sense. Their ideas are something to ponder.

http://www.cbc.ca/ideas/features/living-on-oxford-time/

Thomas Ashby, Calgary (Sent Tuesday, May 26, 2009 5:07 PM)

Re: Deutsch's, Barbour's, and Penrose's perspective.

If there are an infinite number of static universes that hold each 'instant' in time how does conciousness pass from one to the other? How are we aware of this passage (time flow so to speak)? What would be considered to be an 'instant' (universe) in time?

In Cramer's TI theory two quantum waves are involved in any energy transfer one 'requesting' wave incident upon the receiving detector and the 'acknowledgement' wave incident upon the transmitter. This theory would require these waves propogating outside the time-like dimension or very loosely coupled with it (i.e. instantaneously or faster than 2c). The detector would also have to 'know' that it would be the receptor and any other detectors would have to 'know' they are not. A probability wave of some sort would do this without conciousness but then we are back where we started out with probabilities or probability waves cancelling each other out to effect the outcome of the reception of energy.

Rick S. (Sent Thursday, May 28, 2009 2:37 PM)

I was just reading an article at http://www.senseorscience.com/ about time travel that makes me believe that time travel isn't possible, regardless of what the experts are saying.

Jack, Bournemouth, UK (Sent Wednesday, June 24, 2009 6:42 AM)

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