Reverse Time Could Explain Dark Matter

idot writes "According to Lawrence Schulman of Clarkson University, who will get his work published in the Physical Review Letters, the universe could contain reverse-time regions. The article from New Scientist says that this phenomenon could explain the yet mysterious dark matter. " The reverse time regions can help explain the "dark matter" problem because, as potential relics from the future, stars could have re-ignited under The Big Crunch and while we wouldn't see them, we would feel their gravity. Needless to say, more details will be needed then this small article.

Comments

New Scientist Link

[headshrinker]

Seeing as there wasn't a link - for more info, look at http://www.newscientist.com /ns/19991127/newsstory3.html

Details?

[geon]

sounds fascinating, but we have a few more details?

Also, would stuff like this be observable? ie what effects would something like this have?

Re:Cool, so now I can go back in time?

[Rootman]

So what would be first on anyone's agenda in a backwards time travel?

1) Knock off Bill Gates pre MS?

2) Kick all the asses of programmers that insisted on using 2 digit dates?

3) Borrow a few million and invest in the RedHat IPO?

4) Take the current build of Linux and make it a present to Linus back in 1992?

a bit vacuous?

[Noer]

This seems kind of vacuous... it's what I hate about New Scientist... it often tries to avoid any details that might ruin a sensational piece. No mechanism or evidence or theoretical reasoning is proposed here.... just the laws as we currently understand them don't prohibit this sort of thing.

That said... could this reverse time be like a reflection of a wave in time (rather than in space) off the big crunch? does all time just reverse, and thus there'd be a big crunch even if omega >= 1 and the universe is flat or open? Hmmm...

Re:a bit vacuous?

[hobgadling]

I believe what the theory actually says (very hard to tell from this article) is that if there was a big crunch (omega1) then these pockets of reverse time could be formed. One interesting offshoot from this is that if we find these pockets, we would be able to tell for sure whether or not there was going to be a big crunch. ~Adam

This is interesting.

[Millennium]

Does this mean that, the problems with getting there notwithstanding, I could hop into one of these reverse-time zones, hang around for a while, and come out earlier than when I went in? The implications of that are hardly trivial...

Re:This is interesting.

[mmontour]

Does this mean that [...] I could hop into one of these reverse-time zones, hang around for a while, and come out earlier than when I went in?

Sure, provided you had a sufficient supply of carbon dioxide, urine, and feces to consume while you were there...

Red Dwarf's "Backwards" episode covers this in more detail. :-)

Re:This is interesting.

[Johan Jonasson]

Yeah, that would be cool. Again, ignoring the "getting there" problem, we could use these zones to relive the turn of the Millennium over and over again... (Imagine the pain...)

Well, I guess that a reverse-time zone could be useful in other situations as well. I know a few times in the past where I could have made great use of one.

Re:This is interesting.

[Psiren]

Red Dwarf's "Backwards" episode covers this in more detail. :-)

Rimmer: Where's Cat?
Lister: He just... in the bushes... you know...

Lister: We've got to stop him!

A most amusing scene! =)

Re:This is interesting.

[Millennium]

Ah, except that, if I'm reading this right, you would still percieve time as going forward in a reverse-time zone. The only difference is that time flows in the opposite "direction."

You know, I just thought of something. "Normal" time starts from the beginning and works forward. Reverse time, it would seem, must start from the end and work back, flowing at the same rate.

What happens when two adjacent but opposite-flow time zones hit the exact same moment, then? They have to at some point, after all; it's a case of meeting in the middle.

Re:This is interesting.

[PD]

Damn that was *funny*.

I wonder, would a cryptographic one-way function reverse direction of difficulty in a reverse time zone? Would it be really easy to factor large numbers, but really hard to multiply two small numbers?

Would a star located in such a zone actually be *colder* than surrounding space as it used energy to split helium atoms into hydrogens?

Re:This is interesting.

[passion]

trivial if you assume that your entity will remain the same in this reverse universe. What if this flow of time is more like an entropy river that picks you up in it's tide. After all, time passes quicker when we are near a large mass...

What if you got in there, and the direction of entropy in your brain switches and you quickly forget what your plan was... living the rest of your life experiencing only things you remember. And immediatley forgetting what you just did.

Re:This is interesting.

[osu-neko]

According to the article, if normal-time matter collides with reverse-time matter, you get no-time matter.

Incidently, the article talks about reverse time and normal time as being the way matter behaves. I'm not sure that it makes sense to talk about a "zone" being normal or reverse time. The way time is flowing is essentially defined by the behavior of the matter. So there's normal-time matter and reverse-time matter, not normal-time regions of space or reverse-time, except in so far as all the matter in a particular region happens to exhibit a certain behavior. If you enter a reverse-time "zone", you just happen to be normal-time matter in an area predominantly populated by reverse-time matter. Nothing happens to your own arrow of time unless you interact with the reverse-time matter somehow.

--

Re:This is interesting.

[Nyarly]

What happens when two adjacent but opposite-flow time zones hit the exact same moment, then? They have to at some point, after all; it's a case of meeting in the middle.

While this is not as obvious as stated, it is provable. However, I wonder why it should confuse? The regions as described are not co-spacial, and for a moment would be co-temporal. But you and I are co-temporal at the moment. So what?

More interesting, I think, are the implications of entering such a region of space. Not the actual being there, so much, as considering the interface of normal and reverse time. (Now here's a "seems obvious" assertion: One region's reverse time is indistinguishable from the others. Betcha that's not true, but I can't say why...)

What I mean though is, so much elementary physics presumes that time flows in one direction (if not neccesarily at uniform speed). While the interface is singularly thin, there's a width where time is flowing one way on one side and the other on the other. Quick way to be out a watch, if you see what I mean...

Re:This is interesting.

[Nitrogen]

I talked about this to a couple friends of mine, and, correct me if I'm wrong, but it would be impossible to get into one of these things. As soon as you tried to enter, time would reverse to when you went in, and would kick you back out. It would be an instantaneous process. I don't even know if light could enter (I'm not too well informed in many of these areas, as I'm only in high school and haven't taken a physics class). It seems if it couldn't, it would look like a huge mirror. Would that be detectable to people? Maybe under different wavelengths it would be, but we might view it as a planet able to sustain life, in a solar system not unlike our own, when we were actually looking into a mirror image of ourselves. When (if) we tried to go there, we'd hit the limits of the time region, if you want to call it that, and bounce back with the same momentum as we entered with. It might not even be noticable to those on board. As the ship closes in on its destination, it becomes more and more evident that this is actually Earth, raising questions of what happened, etc. On Earth, people would wonder why it suddenly and instantaneously reversed direction to come back. It would be very interesting to see if any of these things are possible.

mean this does what?

[pen]

I have often thought about time travel, but I have come to the conclusion that even if it were possible, it wouldn't lead anywhere. Here's an example:

1. I know how to travel through time.
2. My friend gets hit by a car.
3. I travel back in time and save him.
4. My friend doesn't get hit by a car.
5. I don't travel back and save him.
6. My friend gets hit by a car.

Re:mean this does what?

[Lodro]

You are assuming that time is linear, and that there is only one time 'thread'. What if, for example, multiple time 'threads' could spawn without bound in any direction? I admit that this doesn't neccessarily solve all contradictions or objections to the possiblity of information travel backwards in time, but FFT.

Re:mean this does what?

[bgeiger]

I've always seen it phrased this way.

A man travels back in time to kill his own mother before he is born. Therefore the man is never born, so who killed the mother?

Re:mean this does what?

[mmontour]

A couple of books to read:

Kip Thorne's "Black Holes and Time Warps", which simplifies the discussion by removing the issue of free will. He describes situations where a billiard ball is sent back in time through a wormhole, coming out on a trajectory where it deflects itself from entering the wormhole in the first place. This is a simple enough problem that it can be solved mathematically.

Robert L. Forward's "Timemaster ", which (without discussion of its literary merits) contains an interesting bit where the protagonist figures out a way to save his family from harm by filtering the information going back in time.

The key seems to be that whatever happens, must be self-consistent. So, Forward's version of your scenario might go like:

1. I know how to travel through time
2. A third person says "your friend and a car were involved in an incident at [place] and [time]"
3. I travel back to that place and time, and pull my friend back just before the car hits him, but it still runs over his shopping bag.
4. The third person reports that "your friend and a car were involved in an incident at [place] and [time]".
5. I travel back [....]

In this scenario, I do not change any known [to me] facts about the universe. However, I do ensure that any ambiguous situations are resolved in my favour.

Re:mean this does what?

[esper]

This is a well-known argument commonly referred to as "The Grandfather Paradox". (Standard version: If you go back in time and kill your grandfather before your father is born, you don't exist so you can't do it so you don't and your father is born so you do...)

Personally, I don't believe that any method for information (including living beings) to travel backwards to arbitrary points in time will ever be developed because we don't have it now. (If it could be done, that information would eventually be taken back to before its discovery, someone would leak it to the 'natives', and it would be known from the Beginning.)

Re:mean this does what?

[ralphclark]

This is the "many worlds" or "many histories" interpretation of quantum mechanics.

If this interpretation is correct, (and if travel backwards in time is possible) then all it means is that the time traveller is then forced to live out the rest of his life in the parallel reality ensuing from his intervention.

The reality he comes from, however, still exists as do all other possible realities. So the time traveller is unable to actually change anything; all he can do is pick a different timeline for himself to live in. And even then, other versions of himself will take different actions with varying degrees of success.

The many histories theory quite effectively disposes with the entire concept of free will because in that theory each individual chooses every possible option at each instant.

Consciousness is not what it thinks it is
Thought exists only as an abstraction

Re:mean this does what?

[aenomie]

Read Robert Heinlen's "All You Zombies," for an interesting take on this

Re:mean this does what?

[__aasfhc1949]

Hello:

I was watching PBS a bit ago and I saw an episode of NOVA on time travel. Your situation, or a situation like it, was brought up. Kip Thorne answered that by speaking of billiards; more specifically, about how when one hits a ball, that ball may hit another, and then the ball may fall into a pocket. (sorry if that is a tad confusing) Thorne explained that even if, for instance, I went back in time and saved my friend, as in your example, my action would start a chain reaction that would have me go into the past again, or something to that extent.

Rajiv Varma

Re:mean this does what?

[SuperG]

OK the way I think about time travelling into the past is this:

At any point in time, where a different action could take place, a "time thread" (or whatever) is taken. In it's grossest sense, I decide to ditch work to go to the beach, work blows up the next day: in the alternate thread I went to work, and died, etc.

Now when you go back in time, your impact creates a thread that is now disassociated from the one you came from - it is now impossible to get back to exactly where you came from. Depending on what the impact you create (remember the Butterfly effect - who knows the possible outcomes of your actions, and the greater the time distance, the greater the effect), things may be more or less the same as the other thread, but it WILL NOT BE THE SAME THREAD.

Time travelling forward presents no problems for me. After all, all you are doing is being "absent" for the amount of time you travel. The "absent" part I've glossed over, but hopefully you get my drift.

Re:mean this does what?

[plunge]

I always wondered about Dean R. Koontz's "Lightning." In it, a Nazi travels FORWARD in time, then comes back with a bunch of future weapons and knowledge. This actually seems much more plausible. Any ideas? Complaints?

Re:mean this does what?

[Repton]

[mmontour proposed some books...]

Another book to look at is Axiomatic, by Greg Egan. In particular, the story The Hundred-Light-Year Diary.

[minor spoilers ahead -- just tech, no plot]

Egan considers someone finding a reverse-time Galaxy. If you point a light detector at it, it should lose charge, not gain it. Now consider the effect of blocking the LOS between the detector and the galaxy. (Egan explains this a lot better than I do) Because of the measurable time it takes light to get from the galaxy to the block, or from the block to the detector, and because of the time direction differences, it becomes possible to send information back in time..

Of course, the article doesn't raise the possibility of us receiving light from time-reversed stars.

(cool author, BTW, if you like hard science in your science fiction)

--
Repton.

Re:mean this does what?

[PurpleBob]

You know, that causes a similar paradox. For time travel to be invented, there had to be a time before that (since the Beginning, as you put it) when time travel hasn't been invented. Finally, someone invents time travel, and the invention leaks out into the past, so suddenly everyone can travel through time, and have been able to since the Beginning (define Beginning here as the first time that there's people worth teaching how to travel through time), so there's no reason to invent time travel...

There are two ways I can think of that this paradox would be resolved. The boring one is that time travel is impossible, and therefore time paradoxes don't happen.

The other is the "time threads" theory that other posters here have mentioned. Someone invents time travel, someone goes to the past to give time travel machines to everyone, and that causes a huge fork in the timeline. In the timeline where time travel was invented, life goes on, and it goes on forward. Meanwhile (if such a word applies), in the timeline where the past was given time travel, the people start splitting off all kinds of timelines and things get weird.

There probably wouldn't be too many splits in the "original" timeline. The fact that anyone who traveled through time never came back would be enough to put people off of time travel.

--

Re:mean this does what?

[robwicks]

I think Larry Niven may have it right on the matter of time travel. If time travel which allows one to actually change the past were actually possible, inevitably, enough tinkering would occur that somebody would go back and do something which would prevent the invention of the time machine. Like prevent the species that created it, etc. So time travel probably does not exist, because any species which would invent it evenentually erases itself from history.

Pointer to Phys Rev article

[StupendousMan]

You can find a postscript version of the article on the astro-ph preprint server:

http://xxx.lanl.gov/abs/cond-mat/9911101

I don't understand the physics ... but I find the idea that local dark matter (yes, within our own galaxy) may be remnants of stars from a far-future universe very unlikely.

Re:Pointer to Phys Rev article

[JakusMinimus]

if you don't understand the physics you are not even close to qualified to speculate on the likeliness of the theory.

Rerun of Feynman

[PlaidLady]

This explanation of dark matter sounds a lot like Feynman's explanation of anti-particles -- that anti-particles are just particles moving backwards in time. Also, this theory requires that the universe will eventually stop expanding and contract back into a "Big Crunch." Most calculated values of omega lately have been between 0.1 and 1.0, and the belief that the universe will contract someday is becoming less and less common. (Also, I once saw a calculation that claimed that if the universe could contract, it would have already done so, unable to expand this far.)

Finally, Schulman's calculations haven't been published yet, but the New Scientist article plays like a passage from Einstein's Dreams. Throw in some Feynman and some decade-old cosmological theories, and we get an explanation for dark matter? Seems awfully unlikely to me.

gniht hcus oN

[PhilHibbs]

.emit esrever ni eveileb t'nod I !hsibbur fo daol a tahW

Let me see...

[jd]

1. Time Travel is theoretically possible, BUT has some severe limitations (such as not being able to preceed itself).
2. An antiparticle travelling forwards in time is mathematically similar to a particle travelling backwards.
3. NEVER, EVER add more entities than is needed to explain a phenomina, completely. Even if you're a physicist.
4. Any interaction between a forward-moving and backward-moving "universe" would be instantaneous as far as the occupants were concerned, and therefore completely impossible to detect.
5. String Theory largely negates the need for any "Dark Matter", which was only a fudge factor anyway.
6. A fudge can never justify a fudge. Unless it's the edible kind, in which case, fudge always justifies as much fudge as is present.

Re:Let me see...

[Chacham]

NEVER, EVER add more entities than is needed to explain a phenomina, completely. Even if you're a physicist.

Occum's Razor? I never understood it, let alone believed in it. To not say that another entity is needed is indeed the greater discovery, and therefore the course that needs more proof.

Re:Let me see...

[jd]

Let's see if I can explain the basis behind Occam's Theory.

Ok, try this. Say you notice that apples fall off trees. Now, let's say there are three theories as to why this happens. Let's call these the "Murple" theory, the "Fzoom" theory and the "Quirp" theory.

Now, according to the "Murple" theory, Apples are influenced by the mass of spaghetti in nearby houses, the phase of the moon, and the sunlight, moonlight and starlight pushing down on it.

The "Fzoom" theory, on the other hand, speculates on the existance of a force that pulls the Apple down off the tree, emanating from the planet as a whole.

Finally, the "Quirp" theory predicts that Apples are affected by the same force as predicted by the "Fzoom" theory, but also adds in the effect of Maple Syrup and roast marshmallows.

Let's start with the first two theories. Occam's Razor predicts that the simpler theory that explains the phenonima is the most likely to be correct.

Yes, it's possible to do experiments to filter out the various sources of light, but let's say that we can't do that, for some reason. (Not all theories can be tested that way, such as the reverse time one.) Where does that get us?

Well, according to Occam's Razor, the second theory adequately explains the phenomina, in a simpler form, and so is the more likely to be true. Note that it does NOT say "it IS true". It is an expression of liklihood, not certainty.

Now, let's take the second and third cases. This reflects the case of multiplying entities. Here, the mysterious force accounts for all the behaviour of the apple. The effects of the Maple Syrup and roast marshmallows are, therefore, zero and can be omitted.

This is how additional entities can often be detected. The more you observe them, the smaller they get, until they vanish entirely. In the meantime, they've obscured important relationships and hidden details. That's why they should never be added, until you're certain there's something that simply CAN'T be accounted for with the existing model.

(A case in point is the theory of gravity, where the fact that the strength of a gravitational field at a distance N from a mass is proportional to the area of a sphere of radius N is not shown in the classic equations. Constants have been randomly folded into each other, in a hodge-podge that would win an award for obscure logic today.)

Re:Let me see...

[Chacham]

That was an oversimplified example. Since the second explains the phenomina, the third has only extras. The first however, you left unexplained, and therefore could not be addressed.

Let me explain.

Imagine an apple fell on your head. Theory A is that the Earth as a mass created some force which acted on the apple. Theory B suggests that the direction in which the apple grew and the force with which the wind was blowing cause it to happen.

Theory B suggest that both the apple and the wind, two elements, affected it. Theory A says that the Earth did it. Without knowing of gravity, I would easily choose Theory B. It simply makes more sense.

Using less rather than more is nice, but only when what is already there can sufficiently prove other things. However, if you can explain two phenomina with either one thing or two, using two seems like a better answer.

An example. Imagine an apple fell on your head, and it bounce back up and reattached itself to the tree. Sir Isaac Newton has come and gone and we all understand gravity. The falling of the apple is explained. Would it then make more sense to say another force bounced it back up and attached it to the tree, or shall we try to attribute that to gravity as well?

Basically, I don't see how Occan's Razor says anything different than common sense.

Re:Let me see...

[Otto]

Amazingly enough, you're still wrong, but it's not your fault.

Occam's razor doesn't mean quite what you think it does.

Imagine an apple fell on your head. Theory A is that the Earth as a mass created some force which acted on the apple. Theory B suggests that the direction in which the apple grew and the force with which the wind was blowing cause it to happen.

You're not understanding the fundamental concept. Occam's razor is to pick the simpler "method" in all cases. The whole "entities" thing seems to be confusing you.

Given your example, the easiest explanation is "things fall down". But why do things fall down? Well, loads of possibilities there..

Which is simpler? "A force exists that makes two object attract each other," or "thousands of invisible fairies are pushing the apple really hard"?

The force idea assumes that there's something fundamental going on that you don't understand. There's plenty of evidence for that. The fairy idea assumes that there's a hell of a lot more going on than you understand, and probably more than you wanted to know about as well. :-) Now instead of explaining gravity, you must explain where all these damn fairies came from.

Occam's razor says, basically, to never explain a phenomena with another phenomena for which you also have no explanation. That is what is meant by "Don't unnecessarily multiply entities."


---

Re:Let me see...

[Chacham]

Occam's razor says, basically, to never explain a phenomena with another phenomena for which you also have no explanation. That is what is meant by "Don't unnecessarily multiply entities."

OK, we're getting somewehre. But what do those two statements have to do with each other? The first sentence makes sense. The second however, may sometimes be an outcome, yet it certainly should not be mentioned as part of the rule.

Re:Let me see...

[tinus]

This does apply to scientific explanations though. You make it seem silly by adding silly explanations.

Re:Let me see...

[Otto]

OK, we're getting somewehre. But what do those two statements have to do with each other? The first sentence makes sense. The second however, may sometimes be an outcome, yet it certainly should not be mentioned as part of the rule.

Again, you make no sense. What two statements are you talking about? Use quotes, man...

I guess, you state that the second sentence you quoted should not be part of the rule. I fail to understand you. That IS the rule.

Lets use a quote here.. Hmm.. Quick web search reveals.. well, quite a lot really.. Ahh, this one's good:

Occam's (or Ockham's) razor is a principle attributed to the 14th century logician and Franciscan friar; William of Occam. Ockham was the village in the English county of Surrey where he was born.
The principle states that "Entities should not be multiplied unnecessarily." Sometimes it is quoted in one of its original Latin forms to give it an air of authenticity.
"Pluralitas non est ponenda sine neccesitate"
"Frustra fit per plura quod potest fieri per pauciora"
"Entia non sunt multiplicanda praeter necessitatem"
In fact, only the first two of these forms appear in his surviving works and the third was written by a later scholar. William used the principle to justify many conclusions including the statement that "God's existence can not be deduced by reason alone." That one didn't make him very popular with the Pope.

Okay, I misquoted Occam's razor a bit in my original post. Still, not bad.

Anyway, be a bit more descriptive in your questions, and I'll try to be more helpful in my answers. :-)

---

Re:Let me see...

[Chacham]

I was refering to the first two statements that quoted. I apologize if I was unclear.

Here thay are again:

Occam's razor says, basically, to never explain a phenomena with another phenomena for which you also have no explanation. That is what is meant by "Don't unnecessarily multiply entities."

The "Don't unnecessarily multiply entities." is what I disagree with. If it truly is uneccesary, then the statement is obvious. Otherwise, it only makes sense when it is common sense. Or at least that is how I understood your original explanation.

I have only seen the rule applied twice. And both time I disgreed wholeheartedly with the application. One was in an essay against Creationism. Instead of bring proofs, he called it uneccesary. The other time was too long ago for me to remember the specifics. I just remember his basic statement going something like, "We now have to possibilities. Since possibility A is already used, we apply Occam's Razor and rid Reason B". It was being used as a proof. And that it surely was not.

The original poster said "3. NEVER, EVER add more entities than is needed to explain a phenomina, completely. Even if you're a physicist." You can certainly add more than are needed. Unless what you already have sufficiently explains it. If you are still looking for and answer, a predisposition to use what you already have will lead to false judgement.

Re:Let me see...

[Otto]

The "Don't unnecessarily multiply entities." is what I disagree with. If it truly is uneccesary, then the statement is obvious. Otherwise, it only makes sense when it is common sense. Or at least that is how I understood your original explanation.

Okay, sure then.

Occam's razor IS "Don't unnecessarily multiply entities." And it cannot be used for a proof.

It is a guideline, not a rule as such. The basic meaning behind it says that given two arguements, the simpler one usually is correct. The "usually" is the key. It may not be correct. Gravity may indeed be caused by invisible fairies. Who knows?

Occam's razor is a pretty good argument against Creationism, but not a great one. God created the Universe. Who created god? Nobody, he's always existed. Then why do you need god to explain the existance of the Universe? Why can't the Universe have always existed? The thing Occam's razor shows is that god is unneccesary to explain the existance of the universe. It says nothing about whether god really exists or not. Mainly, I've used this argument to shut up those idiots who try to force the burden of proof of the nonexistance of god onto me. Usually, I can force them to try to prove god exists (you can't, it's not possible) since they claim more "entities" than I do. I claim the Universe exists. They claim that the Universe exists and god created it. Thus they have the burden of proof.

Anyway, it's all that type of thing. Occam's razor, in a sense, _IS_ common sense, but if there's one thing I know to be fact in this entire world, it's that common sense is anything but common. I refer you to my favorite Heinlein quote in my sig...

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Re:Let me see...

[Chacham]

OK, I understand your point.

I disagree that you cannot prove that there is a god in the world. I believe that I can prove it. It does border, however, on what your understanding of time is. If you have a better forum I'd be happy to spar it out with you.

Re:Let me see...

[Otto]

I disagree that you cannot prove that there is a god in the world. I believe that I can prove it. It does border, however, on what your understanding of time is.

Bunk. Of course you cannot prove god exists. God does not interact with the universe in any sense of the word interact. If I were to witness a miracle, it would not prove that god exists, it would tell me that I don't know everything there is to know about reality (which is true). Even if you could point out god, how could you prove that that _IS_ god, and not some other figure? Could be some Hindu deity in another form. I mean, really.


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Re:Let me see...

[Chacham]

Bunk.

I don't think that I can prove it? ;-)

Anyway, when did interaction become a requirement for proof? Are you saying that you cannot prove that a god must exist? That only that a god who actually interacts exists?

Before going further, you must define what a god is. What you can prove is that something outside the physical world exists, and I would call that existence a god.

If I were to witness a miracle, it would not prove that god exists, it would tell me that I don't know everything there is to know about reality (which is true).

If you were to witness a miracle, and not know that is what a miracle, then I could understand your point. However, if you saw a miracle, and knew it was a miracle, wouldn't that knowledge in and of itself proof your belief? Obviously, you meant that a miracle would not prove anything because you would not understand it as a miracle. But then, that statement carries no weight, and you mentioned it for no reason.

You then say that it would tell you that you don't understand enough about reality. That you don't understand enough is obvious, that is why you would be thinking about it. But to say that you don't understand enough about reality, means that you have a predispostion to believe that everything can be explained without a god. Seeing that you have an analytical mind, you would certainly agree that you cannot prove that a god does not exist. With that in mind, I do not understand your comment that everything must have an explanation that you just don't know.

Yay Clarkson!

[Mark F. Komarinski]

I'll add this to the known list of accomplishments:

1) 1-2-3 Jello (remember that?)
2) Get Teflon to stick to pans
3) Artificial blood
4) Clarkson Packet Drivers (now Crynwr?)
5) Galahad!
6) The great sinking science center

Any other CU people out there that can add to this?

But will there be a big crunch ??

[Manifest]

As said in the article(New Scientist),the reverse time region needs an opposite of the Big Bang called the Big Crunch. But will a Big Crunch occur ?? Out of the 3 models by of non-static Universe, Big Crunch is the end-effect of just one of the models, the other being Ever Expanding and just exanding enough to avoid a Big Crunch.

So questions arises, will there be a Big Crunch ??

Manifest

Re:But will there be a big crunch ??

[Wah]

Yes, on Oct 7, 15,456,239,683 at approximately 7:45 in the a.m.

Re:But will there be a big crunch ??

[Robert Link]

A "Big Crunch" seems unlikely given our current knowledge of astrophysics. There are several factors that would seem to argue against an eventual recollapse of the universe. The first is that if we total up all of the matter that we "see", including dark matter detected only through its gravitational effect, we only find about 20% of the critical mass density needed to close the universe. It would be a bit surprising to find that there was another 80% of critical density lurking, undetected even through its gravitational effects.

Another factor that argues against a recollapse is that the time scale test heavily favors open (i.e. expanding forever) models. Basically, for a fixed Hubble constant, closed models are younger than open models. Since the age of the universe derived from the expansion is just barely consistent with globular cluster ages for open models, closed models are real losers unless there is some serious revision in the ages of globular clusters.

Finally, recent measurements suggest that there is a nonzero "cosmological constant", an extra term in the General Relativity field equations that acts as a repulsive counter to gravity. What's more, the measurements seem to indicate that the cosmological constant is not only nonzero, but in fact dominant at the current epoch. If true, and if the cosmological "constant" really is constant (it is typically assumed to be constant with time, but that is not a theoretical necessity) then this would preclude a recollapse, irrespective of the mass density in the universe. (Recollapsing models with positive cosmological constant are possible, but only if the big crunch occurs before the cosmological constant term becomes dominant.)

Re:But will there be a big crunch ??

[Janitor]

Yes, on Oct 7, 15,456,239,683 at approximately 7:45 in the a.m.

Is that a monday? That sounds like something that would happen on a monday.

Re:But will there be a big crunch ??

[MrCreosote]

Of Course - don't you listen to the ads for breakfast cereals???!!!

Re:But will there be a big crunch ??

[apathetic]

yeah, i haven't gotten the hang of mondays yet

Re:But will there be a big crunch ??

[AndrewRF]

Interestingly there was an artic le in today's New York Times Science section that bears some relevance. (Actually there was another related article in last Saturday's (?) Times, but I can't find a link to it. Oh well).

The article more or less says that there is mounting evidence that the Universe is expanding at an increasing rate. If this is true, then it seems to indicate that there won't be a Big Crunch. The source of the increasing speed of expansion is presumably some unknown repulsive force. There is speculation that this is the result of elementary particles popping into and out of existence (compliments of quantum mechanics and Heisenberg's Uncertainty Principle, if memory serves).

Correction and/or additional insights from those with a better grasp of astrophyics?

Re:Cool, so now I can go back in time?

[Lord Kano]

1) Splurge on surveillance equipment and tail Bill Clinton for 18 months circa 1990.

2) Swing past 1992 and warn the "1992 me" not to go out with that bigtime whore that I dated back then.(Yes Jamie, I'm talking about YOU)

3) Win every lottery in every state from 1993-Present.

4) Buy 10000 high capacity magazines for popular firarms before the 1994 ban.

5) Sell those magazines for 1000% profit and dump the proceeds plus my billions from the lottery winnings into the RedHat IPO.

6) Sell my RedHat stock for a 1000% profit and buy 51% of M$ stock and FIRE EVERYBODY, and release the source code to every M$ app ever made ON THE DAY that M$ is found to be a monopoly.

7) Give a copy of the current kernel source to Linus back in 1993.

8) Give a copy of the Colt 1911 and Browning High Power to John Browning in 1890.

I'd die of old age before I finished doing the things that I think should be done to improve things.

LK

Yes, but...

[hwj]

Of course, since we can only imagine the consequences if one could travel backwards in time, it's kind of hard to actually come to any conclusions as to what would happen.

But, in your example, you could make it work if you looked at it this way:

1. You know how to travel through time.
2. Your sister gets bit by a møøse.
3. You travel back in time (and as such, enter into a new timeline/quantum universe/whatever) and save her.
4. Your sister doesn't get bit by a møøse.
5. You celebrate by taking a vacation to Sweden, where you experience the løveli lakes and the wonderful telephone system.

Sure, ideas like timelines or quantum universes are far-fetched. Just theory. Then again, so is time travel, given to our current knowledge. Who knows what's possible?

Yeah, how about some URLs?

[Russ Nelson]

4) Clarkson Packet Drivers (now Crynwr?)
5)

Explanations?

[jyak]

After reading this story, it states that, 'Schulman suggests that they may be relics from the far future. This possibility requires that the expanding Universe eventually starts to contract into a "big crunch". In such a situation, the so-called "thermodynamic arrow of time" may reverse during the contraction, creating order out of chaos--an idea first pro- posed by Thomas Gold of Cornell University. "Because of the opposite-running time, anyone around in this phase would actually see the contraction as an expansion," says Schulman.'

Maybe this could help the explanantions of the big bang and expanding universe theories and how the universe actually came in existence. Or does it just go in a continuous loop of expanding and contacting. Any thoughts?

Yeah, how about some URLs (sigh)?

[Russ Nelson]

"... you should have used the Preview button".

4) Clarkson Packet Drivers (now Crynwr?)
5) Galahad!

ugh

[chaos4u]

first we get the universe is flat and now we get this reverse time anomaly .so now we have a flat universe that has pockets of time that move in reverse to the general flow of time. this somehow coexist with this flat universe where time is generally moving forwards . So what dose this do to the fabric of space ?



music the paint
dancefloor the canvas

Incarnation of Immortality

[Wah]

form Piers Anthony has a character than does this.

"Bearing an Hourglass" IIRC.

Basically all the gods of yore are roles taken over by mortals of various means (Death, War, Nature, Time, Fate).

While the Time guy does have the power to stop time he has the curse of having to live backwards, effectively starting at his current age and continuing until he turns into a baby then disappears. The book actually had Satan lead him to an anti-matter field where he could live his life "normally". Some light fiction.

Regardless, I think it quite likely that such matter exists. Remember the Universe is a very big, very old place, all sort of strange things have happened (cough*life*cough) and most anything is possible, so...

Re:Solution

[MaximumBob]

That's the thing that always bugged me about Terminator. Robot goes back in time, gets crushed. Someone finds the robot's arm, uses it to build Skynet. Skynet builds robot, sends it back in time. Robot gets crushed. Someone finds the robot's arm, uses it to build Skynet. You get the idea.

I'm sure there are lots of scientific ways to avoid circles of causality like that, but I don't know how. That's one of those things (along with conservation of matter) that leads me to think that time travel is a practical impossibility.

Pun Foul!

[SEWilco]

"more details will be needed then this small article"

Please use time puns which do not resemble spelling errors. Then we'll know when to complain about that there than then confusion which thou throw.

Re:Pun Foul!

[battjt]

I'm not criticizing anything I've read today, but I wonder if the amount of criticism of /.'s English and spelling is due to the number of non native speakers that frequent this site? After studying English from a book, you may notice the details a lot more than those of use that gloss over the details.

Joe

Re:Pun Foul!

[SEWilco]

I work around problems with reader postings. I expect better of the /. editors.

Last

[NightHwk]

I beleive the fitting comment for a story such as this would be "Last Post!"
=]

so...

[RainbowSix]

How do you get something "bublished" anyway?

Re:so...

[Calamari Indigo]

I thank you need to use a texas Editor and then write until it's finnish.

Re:Cool, so now I can go back in time?

[SL2C]

On page three of the article (the one by Schulman), in the last paragraph, he asks not this question but a related one - is it possible to learn to know about the future (in the example given, an observer in the opposite-thermodynamic-arrow-of-time region notices that it starts raining in "our" world and subsequently sends a message to us, which we receive before it starts to rain, thus enabling us to close the windows).

Since microcausality still holds (and can be proven for a given theory - such as the standard model, for example), I do not think there would be a way to CHANGE your past.

Rather than that, you _might_ be able to look into your future. However, I doubt that this will be much different from predicting the future by physical laws (in fact it is the same, since he looks at systems where the laws are known).
This would probably have to be a deterministic prediction (I mean one that you can not influence by a "free will" decision) in order to avoid paradoxes. The author refers to an older article for this.

Terminator and Skynet

[georgeha]

Someone finds the robot's arm, uses it to build Skynet.

Wow, I never realized that was how SkyNet got built. I thought it was some kind of defense computer network gone wild, or at the least Micorsoft Windows 2010 beta (Are you sure you want to delete humanity? Yes, No, Cancel).

George

Re:Terminator and Skynet

[MaximumBob]

It was a defense computer network gone wild. It just happened to be based on technology that it invented in the future. Try not to think about it too much. That's the best advice I have. Just watch the pretty explosions.

Re:Terminator and Skynet

[David Gould]

Wow, I never realized that was how SkyNet got built.

Not to flame you too hard, but how could you possibly have missed that? It was almost the entire point of the movie. Or did you only see Terminator and not Terminator 2: Judgement Day?

As I recall, it wasn't stated in the first movie -- it wasn't even known to the characters at the time, except for it being "some kind of defense computer network gone wild", and the entire goal was to save Sarah Connor's life, so John could be born and lead humanity to win the war against the robots, while the Terminator tried to kill her and prevent the above.

The second movie wouldn't have been very interesting, though, if it had just been a repeat of the same "one time traveler protects key person from other time traveler who is trying to change history" plot. It was much more, though: they tried to prevent SkyNet from ever existing, by taking out Dyson (its inventor). He reveals that they were making breakthroughs that they "would never have thought of" based on analyzing a brain chip salvaged from the first Terminator, so they go to blow up his entire company, destroying the chip, the lab, the research, etc.

To the other replies:

Try not to think about it too much. That's the best advice I have.

Come on! That's the most interesting part! Even if it makes your head hurt, you've got to want to think about these things.

It is only alluded to but if true does create a really foul time paradox.

I thought it was much more than "alluded to". I'll grant that they didn't really think through the paradoxes, but the fact that SkyNet was made possible by the brain chip was central to the reasons why they had to blow up the lab, and why Schwartzenegger had to be fried at the end (to destroy the last existing brain chip).

It's true that the paradoxes get pretty nasty: first, the premise has the problem that, if SkyNet's invention was only made possible by analysis of the Terminator's brain chip, then where did the technology "come from" in "the first place", i.e., how can a technology exist without ever having been invented?

Then, if you grant that it is somehow possible for SkyNet and the Terminators to have "created themselves" spontaneously, you get another problem: if they destroyed all the chips, preventing SkyNet from being created, then none of it could ever have happened -- Sarah Connor's life should just go back to the way it was before, with Kyle Reese and the first Terminator never even showing up (and, incidentally, John never being born). But then, if SkyNet is not actively prevented from creating itself, wouldn't it do so again...?

The thing is, these paradoxes sort of cancel each other out: if you reject the idea of SkyNet being a figment of its own imagination, i.e., conclude that, despite what Dyson and the second Terminator said[1], it would have been invented anyway as a result of good ole' human ingenuity, then their efforts to prevent it would have been in vain and everything would still happen exactly as Kyle Reese described it. That seems to be the only way for them to have their memories of the events, or for the events to have occurred at all. This is the "Red Queen's Race" (an Asimov story that refers to the bit in Alice in Wonderland where you run as fast as you can just to stay where you are) view on time travel, which is also the theme of 12 Monkeys -- you can't change history through time travel because anything you do "already happened", and was thus "taken into account", making your version of history a self-fulfilling prophecy.

Another problem is that their trying to prevent it all may not have been a very good idea, given how unpredictable the effects would be. In short, you don't mess with a winner. At least in Kyle Reese's version of the story, humanity won in the end, but if they changed things the wrong way, the war night have still happened but without the happy ending.

Or, for a sort of eerie reality tie-in, you could use the multiple time-lines view, where, up to the end, the movie occurred in a time-line where they succeeded in keeping John Connor alive, but failed to prevent the war, and that time-line branched off when they destroyed the chips, allowing our time-line (the real world) to exist with no Terminators at all.

--
[1] Maybe Skynet created false records indicating that Dyson was the inventor, when in fact it was someone else working independently, so that they would blow up the wrong lab.

David Gould

Does anyone actuall believe this?

[Chacham]

Do you really believe that this exists? Has anything ever been proven or at all practiced? Don't you think that if people traveled back in time that we would know about it? That is no proof, but I may believe that more than any other thing I've heard on the subject.

I believe that time is a measurement, plain and simple. It is the measurement of movement. Just like meters measure distance and grams measure weight. Time is just a mesurement.

If meters were non-existant then the whole world would be zero dimentional; if the grams were non-existant then the whole world would have no weight; if time did not exist then the whole world would not be able to move, it would exist anywhere and everywhere all at the same time.

I will attempt to explain. Take a step. Now you are elsewhere. Were you not here before? Are you there now? Of course not. Remove the time aspect, now you can no longer be in one area or another. Because if you move there was a difference in where you were which could only be reconciled with a time difference. In fact, you do not need to actually move, just the ability to move alone would be a proof that time exists. Therefore, if time did exists, you, and everyone for that matter, would have to be everywhere at once. No thought, movement, or anything could exist, because that would mean that time existed.

Well, time would seem to exist. But, IMNSHO (In My Not-So-Humble Opinion), as a measurement, that's it.

Even to someone who thinks that time travel was possible, I would tell them that time always moves forward. It must. Even when you travel back in time, your existance would still move forward. You are still experiencing more time that you did before the travel. So I never could understand the argument, "I'll fix it and then I'll never actually go back to fix it becuase it was already fixed, etc...". You were there, and you did something, and your timeline is still moving forward, so what you did will always exist. That would means that the same event would happen twice in your timeline. (The only problem is, this in itself would meant that time is a measures, and the theory would therefore disqualify itself.)

Re:Interesting

[Ion-Flux]

Yeah but after a while the decay in sound level/quality is magnified over and over again, so the effect only lasts a very very sort time. Not infinitly, other wise we'd have a perpetual motion system...

Get that cheese to sick-bay!

[jabber]

You know, when science starts sounding like Star Trek, it's time to re-evaluate your assumptions.

I'm all for science in sci-fi, but this sounds like too much fi in the sci... Only Star Trek resorts to the time-travel deus ex machina to make for an interesting show.

Yes, we live in a wonderous and amazing Universe. Yes, technology sufficiently advanced is indistinguishable from magic. But trying to explain a speculative theory with an even more speculative theory is unscientific in the extreme.

Transmeta using alien tech makes for a great joke. Matter traveling backwards thru time?? Please!

Re:Hey, I saw that episode, too!

[Godfree^]

I think (but feel free to correct me if I'm wrong) but New Scientist is an English (as in, not American, not language) magazine, so they probably saw it on UK Gold or something....

Re:Recent data....

[Betelgeuse]

Actually, very recent data suggests that the universe is flat. This means that the universe will stop expanding at time=infinity (which is different than expanding forever, strangely enough :-) ) This implies a cosmological constant, some sort of weirdo anti-gravity-type thing. I don't really understand why dark matter necessarily implies reverse time, but I guess this guy might know what he's talking about. . .

Braneworld better explanation

[scaryjohn]

Just based on the relative simplicities (and i mean relative), i think the darkmatter theory de jour of the "Manyfold Univerise Theory" preprint (posted: Roblimo, 19-Nov) had a much better explanation.

Refresher: that there are other dimensions that don't interact with ours, but whose matter still has mass and generates gravity that we can feel, thus causing the dark matter phenomenon

Even if they figured out that reverse time won't mathematically / quantumly cause the hypothetical annilhation of the universe, there are just too many doors it opens. (now just watch it proved right...) We also can't disregard more conventional theories for dark matter: Black Holes and the possible mass of neutrinos.

With regard to all the discussion of this explaining antimatter:
Antimatter, at least at a surface level is matter that has an opposite spin and charge of its corresponding normal particle... there was nothing in the article to make me think that reverse time has anything to do with it.

from the article:
Although Schulman has shown that a reverse-time region is not destroyed by interactions with a region of normal time,

Matter and antimatter is anhillated to their relativistic particle energies (E=mc^2 and all) when it hits its a particle of its counter-type (e.g. electron and positron).

All the same, it's an interesting read. Just wish I had the time and the physics bkgd to read the final article when it came out.
__

alt.geek

Arrows of time

[Megaboz]

First of all, this seems incredibly flaky. It's possible that it just is because it's a New Scientist article though.

But really, there are several different arrows of time. It seems the one he's talking about is the thermodynamic arrow of time, in which entropy increases from past to future. Another is the psychological arrow of time. That's the one that where we actually perceive time flowing from past to future.

Now comes the interesting part. Unfortunately, I have to admit I didn't come up with this on my own. I think I saw this in Stephen Hawking's A Brief History of Time, but it's been a while so I can't be sure. But the idea is that these two arrows are always pointing in the same direction.

That being the case, this seems even more flaky. Especially the part where the author mentions that "backwards time" areas could collide with "normal time" areas and make an area of space that didn't have any arrow of time at all.

I'm by no means an expert on this stuff, but from the little I do know, it seems extremely hard to swallow.

Try reading.

[_iris]

If you read the article linked to by the posting, not to far, above your posting you would have had your questions answered without filling database space which makes slashdot run that much slower. Also, the money they most likely spend buying more storage space thanks to irresponsible postings, like yours, could go towards purchasing more important things.

Big Crunch = Big Bang

[doublem]

Here's an interesting thought:

Time is just a variable, like any other dimension. Many subatomic particles move independantly of time. (It's even been proposed that there is only one electron, and it's just bouncing through space-time in ways we don't understand.)

What if the Big Bang and the Big Crunch are the same event? We see them as different because we have a Nutonian concept of time instead of a Quantum one. There is a single creation point, and all mater/antimater/energy radiate from that central point. Subatomic particles have been observed moving backwards in time (Or at least acting like they are), so it's not that crazy an idea. What if existance as we know it is the intersection of this event's various influences?

The cosmic Nirvana may hold countless universes, each with a total energy of zero. What if the entire universie is nothing more than this burst of energy, warping and twisting in space?

Fasinating.....

Re:Big Crunch = Big Bang

[Jonathan the Nerd]

It's even been proposed that there is only one electron, and it's just bouncing through space-time in ways we don't understand.

If that theory turns out to be true, I'm going to buy that one electron and make everyone else in the universe pay to use it. :-)

(Sorry about that. I don't actually understand these theories myself, so I'm reduced to telling bad jokes about them.)

If elected

[pyradigm]

I am telling you, my constituents, that if elected I will work my hardest for you and I will stop these confusing 11th dimension conundrums. We dont need to spend any more superstring on crazy dark matter construction projects clogging up our theoretical understanding of the the grand unified algorithm!! Hear me people! If elected I will stop the parks department from hiding 98% percent of OUR universe. If we pay with OUR gravitational fluxing, then WE should be able to exist at the same time! Ladies and gentlemen, vote for me...I want to be your next President of the Space Time Continium.

Re:Solution

[irqzero]

Another problem with time machines that no one seems to think of, is the motion in the universe. I.E. 1. Friend gets hit by a car. 2. You travel back in time with the good intention of saving him. 3. You're both dead. He's a smear on the road, and you are in the vacuum of space, because the earth is not where you left it when you went back in time.

Well, this would disprove a lot of other things...

[srichter]

Well, I think if this is really true, many other things will not work out anymore. There is for example the Special and General Relativity which prohibit such phenomena. There are also Black Holes. How do you make the difference between a Black Hole and "Dark Matter"? So how do yo explain the twin or grandfather paradox?

I think this theory brings up alot more issues then it solves and disproves more then it proves. I would take this discovery with a grain of caution.

Stephan

New physics and the dark matter problem.

[Robert Link]

You make an good point. It is always possible to invent new physics to explain any new phenomenon you happen to encounter. However, this is equivalent to admitting that we know nothing about how the universe works, and that we never can know anything about how it works, since you never know what new phenomenon may crop up next; thus, your theories are incapable of making any predictions. It seems clear that whenever possible we should explain new phenomena in terms of old physics.

In the case of the dark matter problem, however, it seems likely that new physics will be required no matter what we do. The reason why is that if there is a whole passel of dark matter lurking in the haloes of galaxies, it can't be made up of baryons (i.e. protons and neutrons). In order for primordial nucleosynthesis to produce the present-day abundances of light elements, there can be no more than about 10% of critical density in baryons; whereas, the amount of dark matter required to explain the observations is around 20%. In fact, all of the types of matter that we know to exist are unsuitable, for one reason or another, as candidates for dark matter. Thus, if the dark matter exists it has to be some sort of "exotic" matter, which is a little troubling.

So, the question is, which sort of new physics that can explain is the least odious. Besides the dark matter, the contenders are modified Newtonian dynamics ("MOND", in essence a small correction to Newtonian gravitation at low densities), and (I guess) this time-reversed theory. Most physicists find exotic matter to be the lesser of the evils. I don't think this paper will change that. The new theory is sufficiently implausible that it will have to make some pretty strong predictions and have them borne out before anyone will (or, IMO, should) take it seriously. Interestingly enough, MOND has gained a small following because it has made some interesting predictions that have been borne out by observations. Unfortunately I can't recall off the top of my head exactly what they were (a speaker mentioned them as a throwaway comment in a talk here a few weeks ago), but they were the sort of predictions on which the standard model is mute; that is, it neither predicts nor forbids the phenomena that were observed. Unfortunately, nobody has been able to come up with a MOND prediction that would be forbidden by the standard model, so as yet the theory is purely speculative.

If I had to weigh in on the matter I'd say that dark matter is still the best game in town. There are several high-energy physics theories extant that predict an assortment of exotic matter, so there is at least some precedent for dark matter, which is more than the alternatives can say. The smart money is usually on the new theories that bear some resemblance to--or, better still, are incremental refinements of--the old theories; although, that's not to say we shouldn't reserve a small wager for the oddball theories; just don't stake the rent money on it.

-r

Time is a state of matter

[Vaulter]

Doesn't this artical say that time is simply a state of matter? We can't really travel backward in time, because as we do, our matter reverts to its earlier state. Therefore, we can't go back in time without reverting to childhood, embryo, twinkle, etc... So the questions of going back in time to kill our mothers or other time travel parodoxes is mute, as whatever we return to has to have previously happened!

Calvinball!

[Kvort]

This sounds like something from Calvin and Hobbes.

"I hit you with the CalvinBall!"

"This is a reverse time zone. You haven't hit me yet."

"I hit the opposite pole, so this is actually a forward time zone..."

Heh... I miss that strip.

>>>>>>>>>> Kvort

Re:Cool, so now I can go back in time?

[mikael_j]

YES! Finally it'll be possible to build elevators like those in the hitchikers guide to the galaxy =)

Mikael Jacobson

The *Shadowon* Particle

[blackholebrain]

And perhaps there exists a *darkness* particle - say the "shadowon" - that travels 186,000m/s[rev]...at the opposite end of the speed spectrum, with particles at rest being in the middle at zero.

This *reverse time* stuff is about like arguing the existence of my "shadowon"... it adds nothing to any grand unified theory but more complexity - a monkey wrench that fixes nothing. Unless, of course, we open our minds up to the idea of reverse mass, reverse length and distance, and reverse energy... maybe even the square root of negative numbers. >8]

Given that Time and Space are the same

[SkyBorn]

Wouldn't that mean also that these time-reversed regions would have their own physical laws that may not necessarily conform to our accepted physical laws. Not only that, but who is to say that we are not in a region of time-reversed space? We could be going in reverse relative to those outside of this region (ie the time-reversed region)

"small interaction" claim

[ggwood]

Having briefly read Dr. Schulman's paper from the aforementioned web site, one important aspect seems to be left out of current discussion. He says only "Here I use that framework [whole bunch of references] to show that small interaction does not destroy the arrows [of time]." Later he says: "Can this yield causal paradoxes? [Insert example here] ... In principle such signals could be exchanged and paradoxes avoided as discussed in [a reference]. It is also possible that such an interaction would violate the small coupling assumption. At this stage I draw no conclusion."
It seems to me he is talking about sending a few photons to transmit a signal from the reverse time region to the "normal" time region - and he's saying that may be too much! Much less taking something like a spacecraft or a person from one region to the other. Schulman's work does not say anything about such "larger" interactions.
What is a small interaction? You have to read his paper. He has an interaction parameter in his simulaitions, but I can't figure out what it means in terms of a force or an energy and I can't compare it to, say, the energy of a photon or the mass-energy of a person. Perhaps a person more familiar with Schulman's termonology could comment?

For completeness, the URL of the paper is : http://xxx.lanl.gov/cond-mat/9911101 - for MS win users, you can click on 'other formats' and 'create PDF' to view the paper if you have Acrobat affiliated with your web browser.

The Emperor's Timeless Clothes

[Baldrson]

That the "laws of physics" are time-symmetric has been "the emperors new clothes" of physics for centuries but it wasn't until Hamilton that the full generality of relativity was widely recognized. People just didn't want to accept it. Many still act dismayed and amazed when some scientist acts on widely accepted principles of physics that are over a century old.

Time is relative to information structures that underly natural phenomena.

Since we are quite strongly aware of an arrow of time, we must be quite close to a major information structure. "The big bang" is as good a name for this information structure as any. But "the big crunch" isn't likely to be a single isolated structure, anymore than the big bang is. This is much like the "earth is the center of the universe" provincialism of early natural philosophy. There could be enormous, yet distant, information structures with localized artifacts near us producing all manner of "weird" effects. Exactly how this might produce additional gravitation is left as an article of faith by the article in The New Scientist but I find it plausible that "dark matter" is simply one of a virtual infinitude of "weird things" to which our eyes are opened once we've accepted the Hamiltonian Revolution the same way we've accepted the Newtonian Revolution.

Lawrence Schulman isn't the child declaring the emperor has no clothes -- he is the taylor who listened to the child.

Hamilton was the child who, without guile, unleashed a truly weird revolution upon physics.

anti-time...anti energy

[dothead]

I've wondered, under the quantum view of matter energy everything is represented by particles. W and Z particles being force carrying particles for the strong force(I think). Theoretical gravitons for gravity and so on. The particles that make up matter(at least baryonic matter) all have anti equivelannts. I'm sure everyone on /. knows when a particle and it's anti come together they are converted to 100% energy. Now if force carrying particles also have anti's, would they make matter when they come together?

patent it

[/]

Clearly what this physicist should do is file a patent for the "reignition of stellar clouds during massive space-time collapse". Since intellectual property refuses to die, it will likely still apply when the Big Crunch occurs, and he'll file for a federal injunction. The result will be retroactive, and dark matter will cease to bother us in our own time. Hooray.

Reverse Time Implies A Contradiction

[EXTomar]

Isn't there a contradiction in the Theory of Reverse Time?

Just like in the place we live in, time and space are tied but we see it going in a "forward" direction. Reverse Time implies that that in such a place, time and space are tied together going in a "backward" direction. The contradiction is that space is never considered! If time is "backwards" then space must also be somehow "backwards." All we know about space and matter says that "space can be empty(devoid of matter) but no less." "Reverse Time" implies that space is less than empty which is a contradiction. Now there maybe a property of space that allows this, and if there is, lets hear it. :-)

Instead, I subscribe to the "Theory of Null Time". Singularities like black holes support this kind of idea. A singularity of space implies that all matter in a given space exists at one point which can only happen if you distort time into a singularity. A singulatiry of time implies that all matter in a given timeline exists in only one instance of time which can only happen if you distort space into a singularity.

The one thing both "Reverse Time" and "Null Time" try to do is explain the existence of "Dark Matter." I think both theories do it well but "Null Time" is a more coherent theory.

Any other theories or ideas on the subject? This kind of theoretical physics has facinated me much like philosophy. :-)

Re:No, I am first cause I'm in a reverse time zone

[DoomHaven]

It's a shame you got moderated down; I thought this was damn funny.

Anti-Time particles

[Foobaz]

I bet a lot of people (myself included) read this article and thought, "Nice theory, but how would there be reverse-time regions? That doesn't make a lot of sense." I came up with a bit of a theory, so i'll share it.

Imagine particles that act in every way like "normal" particles, but that are going the opposite direction in time. I suppose this means that they have the opposite reaction to events (after all, time is nothing but causality [causes and their effects], right?).

Such particles wouldn't interact very well with "normal" particles for obvious reasons, but would interact very well with each other. So, you'd get anti-time atoms and molecules and stars and galaxies completely seperate from our own.

I was also confused for a moment when i thought, "If these guys are going backwards, then they must be created in the big crunch instead." Then i realized that they aren't actually going backwards, just having opposite reactions to the same things, which would make them appear in every way to be going in the opposite direction. You just have to look at it as cause-and-effect, not the flow of time. Time isn't flowing one way or the other. Stuff just affects other stuff.

In conclusion, this would make it impossible to jump into an "anti-time" zone and go back in time. But OTOH, some of this anti-time matter would be pretty fun to play with. Imagine the implications of having something as simple as a ball made out of it.

Then, if your head is still intact, try designing something mechanical using it. If you come up with anything cool, tell me about it. :)

may be true... but irrelevant

[renard]

The paper is a serious and interesting one. It may be theoretically possible for regions with oppositely-directed thermodynamic arrows of time to exist. But within our own universe there are good reasons to believe that, in fact, they do not.

We observe the real universe to have its origin in a state of extraordinarily low entropy -- immediately after the Big Bang, matter/energy was uniformly distributed throughout its entire volume to the level of one part in 100,000 (the smoothness of the Cosmic Microwave Background radiation, as measured by the COBE satellite). Thermodynamically speaking, then, there was only one way for the universe to go -- towards gravitational clumping, collapse, the formation of stars and galaxies, and other sources of entropy (like us). This establishes the thermodynamic arrow of time for the universe.

The actual existence of regions with opposite arrows of time depends, in Schulman's paper, on the ending of the universe in a Big Crunch. But there are two problems with this.

1. All existing astronomical evidence points to a universe that will expand indefinitely (and may even be accelerating). Even with Dark Matter, there's just not enough mass around to hold it back.
2. Even if the universe were to end in a Big Crunch, there is no reason to think this would be a state of extremely low entropy.

Thus even if the paper is correct it is not relevant, in an astronomical sense.

I'll end by pointing out that there are several less dramatic solutions to the "Dark Matter" problem -- now that we know neutrinos have mass, for example, it becomes pretty easy to imagine that there are other more-massive weakly interacting particles out there, the WIMPs, and that these could easily have evaded our detection efforts to date (good reason to continue upgrading the experiments!). A slightly more daring alternative postulates the existence of "mirror matter" which interacts even more weakly with the ordinary stuff that we're made of. Neither of these types of matter, nor for that matter antimatter, should be thought of as travelling backwards in time.

The source leaves a lot to be desired

[Masloki]

Other articles from the current New Scientist:

Sex is good for athletes before the game
An ice age is coming to Europe
Bringing dinosaurs back to life
The Pill may lead to gum disease
Stress may protect your from loud noises.

I would not consider this publication a valid source for scientific news. In addition, they are publishing an article that has not been subjected to peer review. "Schulman's calculations will appear in a forthcoming issue of Physical Review Letters."

If anyone can find collaborating evidence, I would like to see.

My 2cints

Re:So what happens to the billiard ball?

[mmontour]

Actually, from what I remember, you can't say what happens. There are a family of possible solutions, but no way of telling which one of them will be observed. In other words, mechanics with time-travel is non-deterministic sort of like quantum stuff is.

The family of possible solutions involve the 'original' ball coming in, a 'second' ball coming out of the wormhole and hitting the 'original' one, the 'original' one entering the wormhole, then the 'second' one moving off. The point at which the balls collide is uncertain, as is the final angle at which the 'second' ball leaves.
It's even possible to have a case where the ball may or may not even go through the wormhole.

Consider a ball heading toward a pair of wormhole mouths, exactly perpendicular to the line between them. One solution is that the ball simply passes between them and continues off into space. However, it's also possible for the ball to collide with itself in between the mouths, deflecting itself at right angles into one wormhole mouth, out the other one at an earlier time, then finally colliding with its earlier self and being deflected through another right-angle to continue on its original course.

I tried to do an ASCII-art sketch, but after seeing what 'Preview' did to it I decided to give up. :(
Anyway, read the book as it does a much better job of explaining this.

Like Red Dwarf

[kabrakan]

If any of you had read the Red Dwarf books(the series depicted it differently), you would know an implication of this: The main characters dies of old age, the genius computer sends him to a reverse time dimension(not another part of our dimension), and he comes out 25 years old. I can see commercially-run operations sending thousands of wealthy old people to these regions already!

The paper is online

[incandenza]

"More details will be needed"? Well, more details are available if you read the actual paper at http://xxx.lanl.gov/abs/cond-mat/9911101. I'd expect anyone reporting on this story to mention this, but then again, this is Slashdot...

Virtually all physics papers are published online before they appear in printed journals. Physicists invented the web, remember?

By the way...

[incandenza]

I closed the anchor tag properly in the HTML I submitted, but somehow it was removed.

Time Travel's Information Barrier

[Effugas]

People like to think of going back in time, mainly because of the psychologically tragic reality of 20/20 hindsight.

The problem is the complexity a backwards traversable universe creates.

For example, if one can travel back to 1950, that implies that, somewhere, somehow embedded in either the fabric of the unvierse or in the structure of subatomic particles is the exact memory of where and when everything and everyone was. Perhaps an infinitely growing thread(imagine a pencil leaving a trail as it moves over a paper...of course, some small chunk of the pencil is removed with each motion), or perhaps some kind of structural memory, but somewhere, the State Of What Was has to be preserved.

Sounds rather deterministic, in a universe that seems to have blurriness built into its very design.

Yours Truly,

Dan Kaminsky
DoxPara Research
http://www.doxpara.com

Re:Time Travel's Information Barrier

[Control Group]

But this argument only applies if time is external to the universe (i.e., the universe moves along the timeline). If time, instead, is simply a dimension of travel, this problem doesn't arise. There's no problem of "memory" when you go from your front door to your mailbox and back...that is, there's no reason to think the universe has trouble "remembering" the door is there, or the mailbox is there.

If one considers time as just another dimension which defines the "volume" (yes, i know 'volume' implies exactly 3 dimensions, but i don't know a better word. tesseract, maybe...) of spacetime, memory isn't an issue.

The corollary to which, of course, is that the so-called "arrow" of time is a perceptual limitation of the people observing the universe. Which feeds right into Hawking's "finite without boundary" universe...but I digress.

Re:Time Travel's Information Barrier

[Effugas]

There's no problem of "memory" when you go from your front door to your mailbox and back...that is, there's no reason to think the universe has trouble "remembering" the door is there, or the mailbox is there.

Problem: You just created an entirely deterministic universe. Everything that was(at least) or will ever be(at most) has already been predetermined in your picture of things.

Welcome to the land of PseudoEntropy, where particles appear to follow undefined patterns but in fact are all going according to plan?

A particle with intrinsic randomness can act without memory. A particle without intrinsic randomness has absolute memory, since all effects are determinable...but guess which one physics (and Heisenberg, who is abused on an daily basis) prefers. ;-)

Yours Truly,

Dan Kaminsky
DoxPara Research
http://www.doxpara.com

The big crunch

[heroine]

But isn't the universe that is reborn after the big crunch going to be exactly the same as ours and aren't we merely tied to the molecules of our brains, forever repeating our lives in the same point in time at the same place every time the universe restarts?

Re:Cool, so now I can go back in time?

[mhm23x3]

>4) Buy 10000 high capacity magazines for popular firarms before the 1994 ban.

>8) Give a copy of the Colt 1911 and Browning High Power to John Browning in 1890.

ESR, is that you?

Scheduled for PRL Dec 27 issue

[apsmith]

See:

Opposite thermodynamic arrows of time
for the abstract of this paper about to be published. More articles scheduled for the same issue are available here.

Some interesting problems

[Ektanoor]

So this means that patents and copyrights laws are relatively useless. At least at a Universum dimension...

Ooooooh. I see the future claimers
Copyright 1999 Ektanoor All rights reserved for Past, Present and Future.

Re:Cool, so now I can go back in time?

[Lord Kano]

ESR?

Sounds similar to particle charge

[Raetsel]

Many years ago, I had the good fortune to be introduced to a fellow who's livelihood revolved around particle physics. Yes, he was a PhD; no, I don't remember his name (though I do remember he was from West Germany, to give you a glimpse at the time frame.)

Being a sci-fi addicted adolescent, I asked him about time travel, and could he explain what the current thoughts about it were.

His answer was so beautifully simple, and it went something like this:

• "You know that we can create particles in an accelerator with different-than-normal charges, right? (Right.) Take the positron, for example: It's an electron with a positive charge, just the opposite of what a 'normal' naturally-occuring particle would have. We can create (small) atoms that have different charges, and manipulate their electrical potential as we see fit. With me so far? Good.

  Now, we theorize that the time properties of a particle behave in very much the same manner as the electrical charges. The catch is, if a particle has a different time charge than the matter that makes up our reality (and our detection equipment!), we won't be able to observe it, just the affect it has on other matter as it makes it's journey through time."

With that thought, he left me to fry my mind considering the possibilities. Stars running backward are certainly one possibility, but I think that entropy will continue to be the order of the day until the 'Big Crunch'. Even in a contracting universe, stars will shine, coffee will be spilled, and cups will be broken, all until everything is crushed out of existance. I seriously doubt that there will ever be a time when our lives look like a film run in reverse.

Remember the wizard Merlin in the King Arthur / Camelot tales? He lived his life backwards, and thus could remember what we would consider the future! That was cool.

Entropy

[ParadoXIII]

So what does this do to entropy? Seems to me like, since the total entropy of the universe must always increase with time (and, far as I can tell, this is one of the only things that is completely dependent on the flow of time), areas of reverse time would decrease in entropy.
Is it just me, or does that throw the Second Law of Thermodynamics out the window?

Only two things are infinite, the universe and human stupidity, and I'm not sure about the former.
-Albert Einstein

um.

[jafac]

What about light from stars transmitted through these reverse-time regions? Will it go backwards? (ie. reflect back towards the source)

In that case, we would be seeing large reflective regions of space in the night sky, right?

I wish I had a nickel for every time someone said "Information wants to be free".

Re:Cool, so now I can go back in time?

[ParadoXIII]

I don't know about you, but I don't want my elevator telling me to have a nice day.

yeah really.

[mgX]

i agree.. and slashdot encourages humor!

hehe

[cheese63]

wow, i just spend like 5 minutes trying to use babblefish to translate that... god.

Time machines

[vrmlguy]

Larry Niven provided the best argument against the existance of time machines several years ago. IIRC, it went like this: Assume you build a time machine. When you go into the past, your actions will have various effects on the future. Eventually, one of those effects will be to prevent the building of your time machine.

David Brin wrote a similar story as well, wherein the hero could only sucessfully build a time machine that had the "back-in-time" button disabled.

Does anyone...believe... (Religion of Science)

[belgin]

Like almost all scientific articles, it is a piece of fiction that might be interesting to some subset of people. It might even contain elements of the mythical TRUTH. Barring an assumption that I choose not to make right now (making me unpopular at times), we will never know.

This particular piece of fiction makes sense in a few limited areas, and meshes with some other not too widely accepted explanations of the modern scientific religion. It touches on one of the core beliefs of the science saying that there is a concept called time that we percieve to move in one direction. Many followers of science believe or fantacize that this perceptual illusion is permeable, so stories will continue to be rise about how time is reversable or non-existant. This is because people want that to be true.

Why do I refer to science as though it were a religion? Because it is.

If you deny the fundamental set of assumptions that the scientific method is based on, it is complete fiction. One person makes up a story and meshes it with a story that already existed. A few threads of the new story doesn't mesh well with the old story, so a few details of the old story are declared wrong and a few details of the new story are plucked out and suddenly the two seem to fit. As "time" progresses, more and more people include the new story in their personal views of how the world works and move on until new stories are added and change it again.

If you don't like the theory, fine. Don't adopt it as a part of your personal doctrine of science. 90% of the population in the United States doesn't seem to actually know how science works, so it really shouldn't matter to you unless you are a practicing scientist in that field. If you are, then you will want to look at it as a potential doctrinal change. (Yes, I made up that statistic, based on extrapolation from my own experiences.)

All of that said, no, I don't believe this theory out of hand. Yes, I believe in science (as a philosophy and as a State religion). No, this is not a deliberate troll. I thought I would throw in a perspective that most people don't seem to have.

B. Elgin
"Read at your own risk; feel free to ignore."
B. Elgin

Re:Solution

[coreybrenner]

My ideas about time travel.

--Corey

Re:Cool, so now I can go back in time?

[Deimos_]

Your probably right. Without windows, a computer wouldn't be in as many homes as it is now. But everything has a lifetime, and IMO, its time is up.

1) Knock off Torvalds so he doesn't create you ignorant, stupid bastards. (Without Windows, you wouldn't be here you ingrateful fucker. You're probably in Windows right now.)

Why would you want to do that? Its not his fault, he just wanted to do something and did. He felt that it would be nice if everyone could see what he did and his project was lucky enough to take off. He didn't create us! We came to him!

4) Take Windows 2000 and present it to Microsoft ni 1985.

Even if microsoft had the source code to w2k, they wouldn't be able to even understand it much less use it. There's no way that w2k would run on the hardware back then. They would have no compiler, and even if they did, they would have no platform to run the compilers on. On the other hand, Linux source code still runs on the original hardware it was developed on. Linus might have a bit of a time understanding whats going on, but he's a good programmer, he'd get to it.

That brings us to the ethical part of it. Time should *never* EVER be changed even if we have the capabilities of doing so.

Go back to an original Star Trek series, 'The City on the edge of Forever.' Kirk and Spock go back in time through the Guardian to find McCoy, who is drugged and crazy. In the process, Kirk learns that McCoy would have saved the life of one Edith Keedler(spelling). Edith, a very outspoken young woman (cheeze to the end) leads a pacificm movement after not being hit and killed by a truck when McCoy would have saved her. The movement delayed US entry into WWII, German's finished their heavy water expirements first and BOOM, annihilation. Paradox. I don't know about any of you, but I'm do not want to find out what happens if time/space is violated in such a manner, if at all possible.

Stephen Hawking on Time Travel

[__aasfhc1949]

Hello:

I remember watching an episode of NOVA about time travel on PBS a bit ago. Stephen Hawking said on that program that time travel isn't really probable. He also said if it were possible: "how come there haven't been any time traveling vacationers from the future?" An interesting hyposthesis!


Rajiv Varma

Re:Cool, so now I can go back in time?

[Calamari Indigo]

Actually Thorne (not "Throne") says you *can* back in time with this method. Go back and reread it :-)

Re:Hey, I saw that episode, too!

[kallisti]

The first use of the concept I'm aware of is Philip K. Dick's Counter-Clock World. I also remember a short story (Philip Jose Farmer, maybe) where a man watches the unmaking of the pyramids. Piers Anthony used a reverse-time region in the second Incarnations book, Bearing an Hourglass. So its hardly new to Red Dwarf, which shows LOTS of PKD influence IMHO.

yes but...

[decomp]

While your sentiment is undoubtedly worthwhile, it would probably be a good idea to avoid spelling mistakes when criticizing others' spelling and grammar.

vacuous article / pseudoscience

[poincare]

I'm very under impressed with this article. *Most* of the laws of physics are symmetric with time, the exceptions being strange things like kayons. That a particle is moving twards more order (which the author implies) doesn't mean that it didn't have a past or doesn't have to play by the rules of the rest of mater in the universe. People who think about dark matter are worried about what type of stuff it is (weakly interacting massive particle [wimps], nutrinos, gas clouds, etc). What that stuff may be doing in our future (its past?) doesn't solve the basic question of what it is.

We already know what matter moving backwards in time looks like, and we've created it in labs. It's called antimatter.

I did read it.

[geon]

At the time I was posting there were 0 (zero) replies to the article. Apparently the script that generates the page had not updated yet.


Some time significantly AFTER I posted, someone finally posted a link to the preprint of the paper - which is what I was asking for.

The reason I had to ask for info is that the slashdot peeps didn't put up a link to any substance-filled info, like a preprint.

Seriously, think before you loose the flames - otherwise you tend to make an idiot of yourself.

Boors like you is the reason I've grown to be highly critical of slashdot.

Re:Solution

[tonhe]

Skynet you sure that isnt Skyenet, a local isp in my town ?
Maybe they're related... oh shit, better run...
http://www.skyenet.net

~tony

the effect changes the cause

[johnrpenner]

they're finally catching on... about ten years ago, came to the conclusion that casuality runs "backwards" through time -- but its really us that are going backwards through time. what we call reverse-time is actually forwards time. therefore the statement "the cause changes the effect" is incorrect; it would be better to say, "the effect changes the cause!". :-) regards - http://home.earthlink.net/~johnrpenner/

Re:Cool, so now I can go back in time?

[dexter_goodfeather]

but not to any point in time, just to the corresponding times on each end of warmhole

Re:Solution

[tomservo3000]

"For those interested it is the easiest way of getting time travel. One day you come home and find all the plans for a time machine - you build it and then return to leave the plans for yourself (the exact pieces of paper)"

Ok, first of all, I believe that this can't happen, because, quite frankly, knowledge can't create knowledge. You can't say that we learned time travel because our future selves told how to do it. How did they learn it? Let's say that they discovered it, around 2500, and then went back in time and gave the blueprints to us, in 1999. This would certainly change what is the present for the time travelers (2500), since they had time travel capabilities since 1999, and didn't need to discover it in 2500. By giving us the blueprints, they affected their timeline, begining in 1999, all the way up to their present (2500).

But that's one possibility. If there is only 1 universe (no parallel universes), and our changing of the past affects the future, then we have serious problems. Many, many paradoxs can arise, such as the going-back-in-time-and-shooting-myself paradox that everyone loves.

Richard Feynman addressed this issue once by implying that one simply cannot change the past. The example he gives is of a time travler (or chrononaut? is that a word) who goes back 5 years in time and attemps to shoot her past self. However, she misses the heart, and the bullet hits her younger self in the shoulder. Why did she miss? Because her aim was affected by her shoulder - the time traveler was shot in the shoulder 5 years ago.

The other option is that there are parallel universes, and that they are spawned for every possible action in the universe at any given time. If this were the case, and you went back in time and shot yourself, you simply would be dead in THAT universe. You're still alive and well in your own, even when you returned to your own time.

Just one more issue to address - one may say, "Hey, let's say that you are 20, and you go back in time to when you were 10, then aren't there two of you in the same universe? If you met your past self, wouldn't you faint or destroy the universe like in Back to the Future 2?" Well, i'd have to say no. You wouldn't faint, nor would you destroy the universe. I don't think anything would happen, except for the fact that the 20-year-old you would be staring into a 10 year young mirror. Also, keep in mind, you can't be in 2 places at once. Even as you are there, staring at your younger self, you are NOT where should should be (in the future). You are present in the past, yet missing in the future, even for only a split second, so it evens out. And remember, time is all relative (I hate time). So don't worry that your extra mass (that is in the universe at the time you're visiting your younger self) isn't going to cause a sudden cosmic crunch :-)

A little bit about time

[tomservo3000]

I'm reposting this so that hopefully it'll get seen a little better. Besides, it's not completely a direct response, mostly a discussion of some questions that come up about time travel. I made an addition also.

"For those interested it is the easiest way of getting time travel. One day you come home and find all the plans for a time machine - you build it and then return to leave the plans for yourself (the exact pieces of paper)"

Ok, first of all, I believe that this can't happen, because, quite frankly, knowledge can't create knowledge. You can't say that we learned time travel because our future selves told how to do it. How did they learn it? Let's say that they discovered it, say around 2500, and then went back in time and gave the blueprints to us, in 1999. This would certainly change what is the present for the time travelers (2500), since they had time travel capabilities since 1999, and didn't need to discover it in 2500. By giving us the blueprints, they affected their timeline, begining in 1999, all the way up to their present (2500).

But that's one possibility. If there is only 1 universe (no parallel universes), and our changing of the past affects the future, then we have serious problems. Many, many paradoxs can arise, such as the going-back-in-time-and-shooting-myself paradox that everyone loves.

Richard Feynman addressed this issue once by implying that one simply cannot change the past. The example he gives is of a time travler (or chrononaut? is that a word) who goes back 5 years in time and attemps to shoot her past self. However, she misses the heart, and the bullet hits her younger self in the shoulder. Why did she miss? Because her aim was affected by her shoulder - the time traveler was shot in the shoulder 5 years ago.

The other option is that there are parallel universes, and that possibly they are spawned for every possible action in the universe at any given time. If this were the case, and you went back in time and shot yourself, you simply would be dead in THAT universe. You're still alive and well in your own, even when you returned to your own time.

Just one more issue to address - one may say, "Hey, if you go back in time, say to when you were 10 (and you are 20), then aren't there two of you in the same universe? If you met your past self, wouldn't you faint or destroy the universe like in Back to the Future 2?" Well, i'd have to say no, you probably'd no neither. I don't think anything would happen, except for the fact that the present you would be staring into a 10 year young mirror. Also, keep in mind, you can't be in 2 places at once. Even as you are there, staring at your younger self, you are NOT where should should be (in the future). You are present in the past, yet missing in the future, even for only a split second, so it evens out. And remember, time is all relative (I hate time). So don't worry that your extra mass (that is in the universe at the time you're visiting your younger self) is going to cause a sudden cosmic crunch :-)

Btw, the above assuptions (the 20 year-old visiting his 10 year-old self) are made with the assumption that we're dealing with 1 universe here, as opposed to parallel universes.

Re:Cool, so now I can go back in time?

[gohan]

Okay so there are regions of space that time flows backward...maybe I'm just the village idiot but if we're dealling with four dimentions...last time I checked we are...doesn't that go against quantum physics

Transactional Interpretation of Quantum Mechanics

[Eivind Eklund]

It is interesting (and hopefully relevant) to note that the notion of 'reverse time' is also necessary for what is in my opinion the most elegant and easy to use interpretation of quantum mechanics: Kramer's Transactional Interpretation of Quantum Mechanics.

This interpretation does not need observers (as in the standard Copenhagen interpretation), and thus do not suffer from the problem of needing infinite observers (in order to collapse the observer, you need an observer, who need an observer, who ...).

The only concession it makes is that some particles (moving at the speed of light, and thus not experiencing time) need to move backwards in time. This is, in my opinion, a nice tradeoff.

Eivind.

First Post!

[Russ Nelson]

Bwahahahahaha! I got the first post!
-russ