Is time travel possible?

[Dertulm]

I do not know how many of you out there would have heard about Quantum Physics . It is one of the hot-and-happening topics in the field of science . For those who have not heard about lt , who would be very few , I will share what little I know and I will be brief.

According to Quantum Physics , for every second that passes , a parallel universe is created . Not even a second , for every miniscule fraction of time passed , another universe is created . Then imagine the number of universes that would have been formed by now and are forming now , even as I am typing and even as you are reading.

The following information , I will be quoting from Michael Crichton's novel "TIMELINE":
" There is no such thing as time travel . The only way to go into the past or into the future is to travel to another parallel universe . In one parallel universe(also referred to as multiverse) Adolf Hitler is dead , in yet another he may be alive."

The above information I have not quoted exactly from TIMELINE but the content is the same as far as I can remember.
And those who are interested in the topic of multiverse , TIMELINE is a must read. Excellent book.

For those who believe that time travel is traveling only through time and quantum physics is rubbish , please post your arguments.

And others who support the theory of quantum physics , please do give additional information.

[Qadgop the Mercotan]

Um, if you're getting your understanding of quantum physics from Michael Crichton, I fear that you will find that actual quantum physics is much, much different.

I'm certain a few of our actual physicists will be along soon. While I hold the same degree as Crichton, I won't presume to muddy the waters with an oversimplified explanation.

Welcome to SDMB!

[Der Trihs]

According to Quantum Physics , for every second that passes , a parallel universe is created . Not even a second , for every minuscule fraction of time passed , another universe is created .That's only the Many Worlds Interpretation of quantum mechanics; there are others that don't involve parallel universes. And no one knows which interpretation is true, as of yet.

The following information , I will be quoting from Michael Crichton's novel "TIMELINE":
" There is no such thing as time travel . The only way to go into the past or into the future is to travel to another parallel universe . In one parallel universe(also referred to as multiverse) Adolf Hitler is dead , in yet another he may be alive."

The above information I have not quoted exactly from TIMELINE but the content is the same as far as I can remember.That's . . . a novel. Not a physics textbook.

For those who believe that time travel is traveling only through time and quantum physics is rubbish , please post your arguments. You aren't defining quantum physics correctly, or time travel. Those are arguments.

And to answer the question, "Is time travel possible ?", no one knows. I've noticed over the years that physicists keep tossing up ideas for time travel, and others keep shooting them down. I'm reminded strongly of the era before the laws of thermodynamics were formulated, and a perpetual motion machine was considered a reasonable thing to try to invent, and many smart people tried; they didn't know why it was impossible. I wouldn't be surprised if there's some undiscovered law of conservation that prevents time travel.

Or, perhaps not, and time travel really is possible. Bottom line, we don't know for sure.

[AHunter3]

We just did this recently. Here was my take on it (http://boards.straightdope.com/sdmb/showthread.php?p=9529731&highlight=time+travel#post9529731)

[Mosier]

Quantum physics just means "physics involving things that are really, really small". It doesn't suggest or prove that there are zillions of parallel universes, only that there MIGHT be zillions of parallel universes.

The definition of "universe" is "everything that observes, is observed by, or interacts with anything". Different universes would exist separately from ours. If it were possible to move between universes or observe them or interact with them in any way, they wouldn't be universes anymore, but rather just one singular universe.

[peekercpa]

I do not know how many of you out there would have heard about Quantum Physics . It is one of the hot-and-happening topics in the field of science . For those who have not heard about lt , who would be very few , I will share what little I know and I will be brief.

According to Quantum Physics , for every second that passes , a parallel universe is created . Not even a second , for every miniscule fraction of time passed , another universe is created . Then imagine the number of universes that would have been formed by now and are forming now , even as I am typing and even as you are reading.

The following information , I will be quoting from Michael Crichton's novel "TIMELINE":
" There is no such thing as time travel . The only way to go into the past or into the future is to travel to another parallel universe . In one parallel universe(also referred to as multiverse) Adolf Hitler is dead , in yet another he may be alive."

The above information I have not quoted exactly from TIMELINE but the content is the same as far as I can remember.
And those who are interested in the topic of multiverse , TIMELINE is a must read. Excellent book.

For those who believe that time travel is traveling only through time and quantum physics is rubbish , please post your arguments.

And others who support the theory of quantum physics , please do give additional information.

Time travel is definitely possible, but only on that island where the dinosaurs are present.

[Alessan]

Quantum physics just means "physics involving things that are really, really small". It doesn't suggest or prove that there are zillions of parallel universes, only that there MIGHT be zillions of parallel universes.

The definition of "universe" is "everything that observes, is observed by, or interacts with anything". Different universes would exist separately from ours. If it were possible to move between universes or observe them or interact with them in any way, they wouldn't be universes anymore, but rather just one singular universe.
So if we discvered a method to travel between previously seperate universes, we would be in effect be joining them together?

[Mosier]

So if we discvered a method to travel between previously seperate universes, we would be in effect be joining them together?

If universes can affect and be affected by other universes, they wouldn't be separate universes. The hypothetical is kind of loaded though. It would be like saying "hypothetically, if we could violate the conservation of mass/energy laws and create matter out of nothing, we could burn it as fuel and never have to use oil again!"

Well, yeah, we could, but the big deal isn't the oil independence, it's the fact that literally everything we know about physics has just been proven false. It would be impossible to learn or know anything, because the universe wouldn't be consistent or permanent anymore.

[msmith537]

We just did this recently. Here was my take on it (http://boards.straightdope.com/sdmb/showthread.php?p=9529731&highlight=time+travel#post9529731)


So IOW, through the magic of the "Search" button, time travel is, in fact, possible. At least in the universe of the SDMB.

[Dertulm]

As I have pointed out earlier my knowledge on this subject is limited. And I too am not telling that there is definite proof of multiple universes existing, I only quoted the content of TIMELINE.For that matter , isn't almost everything in physics theoritical? Is there proof that we are the only inhabitants of this universe? Leave aside the universe , is there proof that we are the only inhabitants with the so-called six senses on earth? We do not know what lies beneath the bowels of earth. We are assuming that just the lower strata of organisms are living below, what if thay were a superior race to us.
Ok . Coming back to the present topic. I know that TIMELINE is not a textbook ,but in each and everything is there not an iota of truth ?

And comparing time travel with the existence of multiverse , I think knowing that we do not even know the size of our universe,the probability of a multiverse existing becomes even higher.

[BrainGlutton]

Larry Niven once wrote an article on the thesis: If the physics of a given universe of discourse permit time travel, no time travel will be discovered in that universe of discourse. Reason being, so many people have so many reasons to want to change the past, they'll keep doing it -- until some time traveler's interference shuts down the process by producing a timeline where nobody ever discovers time travel.

This thesis, of course, was based on the unspoken assumption that changing the past would be the only reason anyone would want to visit it, which is obviously not true. We can imagine a universe of discourse where time travel is possible but changing the past is impossible -- if you try to stop Booth before he shoots Lincoln, something will happen to prevent you. Heinlein's Time Enough for Love is set in such a universe -- Lazarus Long takes a trip back to 1917 just to visit his old family; he has no history-changing mission, nor is he the least bit concerned he might change history, because he knows he can't.

[Der Trihs]

If universes can affect and be affected by other universes, they wouldn't be separate universes. That's an archaic, or at least highly debatable definition of the term.

[Contrapuntal]

I do not know how many of you out there would have heard about Quantum Physics .I think seven of us have. Maybe eight.



It is one of the hot-and-happening topics in the field of science . And has been for eighty some years, at least.

[glee]

As I have pointed out earlier my knowledge on this subject is limited. And I too am not telling that there is definite proof of multiple universes existing, I only quoted the content of TIMELINE.For that matter , isn't almost everything in physics theoritical?


Everything in science (which includes physics) is based on observation and evidence.
Sure scientists form theories and make predictions. And wait patiently for confirmation. We haven't studied a black hole up close, but we can make assumptions based on distant observations.


Is there proof that we are the only inhabitants of this universe?


Is there proof that we are all living in a computer simulation, controlled by computers and that we are waiting for Neo to rescue us?
Well, no (to both).
Who says we are the only inhabitants of the universe?
You may be confused by the fact that some people claim that alien UFOs have visited us, but scientists point out there is no proof of that - which doesn't mean they are ruling out aliens everywhere.


Leave aside the universe , is there proof that we are the only inhabitants with the so-called six senses on earth?


Who says we only have six senses?
Can you detect heat? What sense are you using?
Can you tell when you are being tilted? What sense are you using?
Can you feel pain? What sense are you using?
Can you touch your nose blindfold? What sense are you using?


Ok . Coming back to the present topic. I know that TIMELINE is not a textbook ,but in each and everything is there not an iota of truth ?


How do you know TIMELINE is not a secret textbook?
How do you know the Illuminati are not controlling all the countries in the World and using time travel to enforce it?
How do you know that the the author isn't pretending it's fiction, because it's the only way to fight them?

1. If there is truth in everything, then the statement 'We know nothing' must be true.
2. But if we know we know nothing, then we know something. Therefore there is no truth in the statement.
3. But if we know the statement is false, then we know something. Therefore the statement is both true and false simultaneously. (And that beats the hell out of Quantum Physics.)

[E-Sabbath]

As I noted in the linked thread, time travel is entirely possible, theoretically. I even showed how to do it.

[Wendell Wagner]

Please ignore any scientific claims made in _Timeline_. In fact, please ignore any scientific claims made in any of Michael Crichton's novels. Crichton, despite having a medical degree, tends to mess up any science he uses in his novels. It always sounds to me that he's using information that he read five years before in a newspaper article that was a bit vague itself. If you want to learn about quantum physics, get yourself a popular introduction to the subject and read it. Don't try to learn science from novels. Perhaps other posters can suggest some good popular introductions to quantum physics.

[Great Dave]

Time travel is theoritically possible, but you can only go back in time to when the machine was turned on, but no further.

[XT]

As I said in the other thread on this topic I think it IS possible...theoretically. However all of the various schemes I've seen to actually do it require pretty much magical technology (you know the drill...to paraphrase 'Any highly advanced technology is indistinguishable from magic' to the poor slob trying to observe it). The one most interesting I've seen lately was on the Science Channel where a physicist (who's name currently escapes me) is trying to create a time machine using bended light. As Great Dave says it could only go back to the point it was originally turned on at (assuming it was left running)...and currently they are trying to send a PROTON back through it...and even that is probably years away. Not exactly Timeline....

As to the many worlds thingy...again, it's theoretically possible that A) There ARE many alternative universes, B) That universes that has time that moves slower than our own but otherwise is similar, C) That we could travel between these universes in some magical fashion someday.

However the technology to even DISCOVER if there are alternative universes is centuries beyond our current capabilities...let alone having the mechanism (if it's even possible) to travel between them.

For the foreseeable future it's simply an interesting topic without anything more than very tenuous underpinnings. Just something for physicists to talk about at cocktail parties and such...

-XT

[Mosier]

That's an archaic, or at least highly debatable definition of the term.

What other definition of universe is there? There's nothing archaic about calling it "the whole of the causally connected spacetime", which basically means "everything that observes or interacts with everything else". If two universes were causally connected by something like time travel, what definition of "universe" could you use to justify identifying them separately?

[glee]

Time travel is theoritically possible, but you can only go back in time to when the machine was turned on, but no further.

Cite?

[E-Sabbath]

See previous thread, Glee.

[Great Dave]

glee,
Listen to the second act this episode (http://thislife.org/Radio_Episode.aspx?sched=1227) of This American Life about Ron Mallett. (http://en.wikipedia.org/wiki/Ronald_Mallett)

[vison]

One of my first online friends was a physicist who, in real life, was, among other things, a sometime "technical advisor" to STNG and some scifi movies. I was writing a story in which my protagonist invented a Time Machine. I asked Mr. Physicist for advice, adding this comment, "I guess it would take a lot of energy" and, among other things he said, he said, "More energy than can be imagined". He went on to discuss Dark Matter and a few other things and ended by advising me to do what scifi writers have always done: more or less wave your hands and say, "He invented a time machine and went back/forward in time and this is what happened." I took his advice. He didn't say "it's impossible" but he did say, "it's unlikely because . . ." and the because was mostly because of the vast, unthinkable amounts of energy required to move anything, even a proton, through time.

[RaftPeople]

Time travel is theoritically possible, but you can only go back in time to when the machine was turned on, but no further.

I thought you could go to any time you could key into the radio in your DeLorean, but you always had to watch out for some guy named "Biff".

[Skald the Rhymer]

This thesis, of course, was based on the unspoken assumption that changing the past would be the only reason anyone would want to visit it, which is obviously not true. We can imagine a universe of discourse where time travel is possible but changing the past is impossible -- if you try to stop Booth before he shoots Lincoln, something will happen to prevent you. Heinlein's Time Enough for Love is set in such a universe -- Lazarus Long takes a trip back to 1917 just to visit his old family; he has no history-changing mission, nor is he the least bit concerned he might change history, because he knows he can't.


No, he THINKS he can't. The time travel trip in TEFL is Long's first, and he knows of no others; his opinion that he cannot change the past is based entirely on speculation. Admittedly it's presented as incontrovertible, but that's because the time travel story is told almost entirely from Long's POV, and he's certain he's correct. As the story is constructed, it is impossible to tell whether the Lazarus Long of circa 3000 AD Secundus was present in the "original" 1910s of the story, or whether his simple presence was a change.

[Mijin]

Der Trihs: "That's an archaic, or at least highly debatable definition of the term."
What other definition of universe is there? There's nothing archaic about calling it "the whole of the causally connected spacetime", which basically means "everything that observes or interacts with everything else". If two universes were causally connected by something like time travel, what definition of "universe" could you use to justify identifying them separately?

Does it matter?

Whether we call these pockets of spacetime "universes" or not doesn't affect Dertulm's (wild) speculations in any way.

What we really need is another term for alternate/parallel universe, one that doesn't imply isolation because there is speculation that this may not be the case. I don't think there is an established term for this though, so "universe" has to do in the meantime.

[Mosier]

One of my first online friends was a physicist who, in real life, was, among other things, a sometime "technical advisor" to STNG and some scifi movies. I was writing a story in which my protagonist invented a Time Machine. I asked Mr. Physicist for advice, adding this comment, "I guess it would take a lot of energy" and, among other things he said, he said, "More energy than can be imagined". He went on to discuss Dark Matter and a few other things and ended by advising me to do what scifi writers have always done: more or less wave your hands and say, "He invented a time machine and went back/forward in time and this is what happened." I took his advice. He didn't say "it's impossible" but he did say, "it's unlikely because . . ." and the because was mostly because of the vast, unthinkable amounts of energy required to move anything, even a proton, through time.

I've noticed that physicists don't like to talk in absolutes. I don't think I've ever heard a physicist say that something is "impossible".

[Cyberhwk]

I always thought that if time travel was really possible, don't you think someone would have traveled back in time to tell us how to do it by now?

[DrCube]

Time travel is 100% possible. Hell, I'm traveling through time right now!

[GuanoLad]

I always thought that if time travel was really possible, don't you think someone would have traveled back in time to tell us how to do it by now?That's where the theory of "you can't go further back than the invention of the time machine" comes in.

Or the theory that you can only go forward in time.

Or the theory that people have been going back in time to our present, but have successfully restrained themselves from altering history by inventing the time machine earlier than it was actually invented

Or it's a physical impossibility to alter the timeline when there's only a single linear thread of time. What happened happened, and subverting time by inventing time machines before they were invented is not possible.

[BMalion]

Time-travel is fairly simple to work out. many scientists have figured out the tehnology and lots machines have gone backwards and forwards through time.

Unfortunately they never realized that as you into the past or the future you materialize in deep space because the earth has been moving.

Pity.

[Bryan Ekers]

Is time travel possible?

Let me get back to you.

[BMalion]

paging John Titor...

[Stranger On A Train]

As I have pointed out earlier my knowledge on this subject is limited. And I too am not telling that there is definite proof of multiple universes existing, I only quoted the content of TIMELINE.For that matter , isn't almost everything in physics theoritical? Is there proof that we are the only inhabitants of this universe? Leave aside the universe , is there proof that we are the only inhabitants with the so-called six senses on earth? We do not know what lies beneath the bowels of earth. We are assuming that just the lower strata of organisms are living below, what if thay were a superior race to us.
Ok . Coming back to the present topic. I know that TIMELINE is not a textbook ,but in each and everything is there not an iota of truth ?I'd like to participate in this discussion, but unfortunately I left my tinfoil beanie at home today and I don't want the CIA to scan my brain with their mind control rays.

I will note, however, that the interpretation (such as it can be parsed) presented by the o.p. is similar to Hugh Everett's Relative State interpretation, later expanded to and better known as the Many Worlds interpretation, later popularized by Bryce DeWitt and serving as the basis for many a science fiction story. The idea is that instead of Bohmian-type ontological theories (in which the uncertainty in the prediction and measurement of quantum interactions is due to predetermined nonlocal hidden variables or connections) or Copenhagen theories that involve the collapse of probability wavefunctions into events (whatever that means), the wavefunctions don't collapse at all but instead interact, giving a resultant series of events spread across different "world lines" like the interference patterns of two waves in a pond from pebbles dropped at the same time.

Note that Everett himself never gave any indication that he believed in the literality of multiple universes, and especially not ones you could truck back and forth between like a character in a Philip K. Dick novel; his proposed interpretation merely eliminated what he considered the ad hoc framework of waveform collapse (which has no observable physicality) with a real, objectively decohered state of all that was one of an infinite number of such states. This has the advantage of essentially adopting what is equivalent to a ontological or nonlocal hidden variables interpretation but without the baggage of casual connections between nonlocal particles or events and the attendant paradoxes; eliminating the entirely arbitrary waveform collapse upon observation business; and dispensing with solipistic noodling of "Consciousness Causes Collapse" or the absurd bookkeeping of Consistent Histories. It also fits in nicely with both the Transactional interpretation (insofar as that all the forward and backward interactions of standing waves in time are entirely consistent with RSI/MWI) and in effect with quantum field theories, which simply resolve probability wavefunctions into a smear of all possible paths as fields while mostly skipping lightly over the tricky mathematical sticking points and worries about what goes on behind the curtain.

However, the net result is really no different in execution than any of the other dozens of major interpretations and variants; that is to say, you still have to treat every event as a statistical operation without a deterministic mechanic. Because of this, we have no way to validate one interpretation over another, and thus physics students are mostly taught the Ensemble interpretation, also colloquially known as "Shut up and calculate!" because it works without having to go over to the Philosophy department for endless tiresome arguments over whether the Moon is really there even when you aren't looking at it.

As for whether you can travel in time, certainly you can, and in fact, you can't stop it. You can travel forward in time relative to any hypothetical "objective" reference frame at any ratio between 1:1 and ε:1, with ε being any arbitrarily small number that is dependent on how fast you are going and how bent the intervening space is between you and the objective reference frame in question. Generally speaking, you cannot go backwards (retarded) in time in such a way as to exist in two causally connected points in spacetime simultaneously. It is possible in General Relativity (which has nothing to do with quantum mechanics) to construct solutions in very warped regions of spacetime in which you have a space-like path that would, from the viewpoint of an omniscient observer appear to be going back in time; however, like a Ferris wheel, you can't just get off at any arbitrary point (or so it is assumed), but instead have to ride back around to your entry point or beyond, thus negating any practical value of such travel. It is also possible to create constructs which connect nonlocal regions of spacetime together, creating was is essentially a workaround for traveling through time/faster than light/whatever, but you either have to assume that they already exists, or that you can arbitrarily create new connections, or otherwise postulate some kind of beyond-magic formulation of fundamental nature.

Locally (that is to say, in the space that you can immediately interact with and observe) you can't go backward in time without violating the laws of thermodynamics, which apply to all events except maybe Dick Clark. And if you do manage to violate the laws of thermodynamics, Maxwell's demon will come out and bite your head off, so I wouldn't recommend it, despite the short-term profit from perpetual motion devices.

Stranger

[BMalion]

Don't forget the time dilation effect. As soon as we have nearly light speed travel (no doubt just around the corner) you'll be able to travel far into the future while everyone on Earth is long dead and forgotten. Of course, it's a one-way trip but hey, whattaya' want? It's the future!

[JohnnieEnigma]

Of course it's possible... it happens every day. When I fly from NY to Rome, I'm traveling through time. :cool:

[vison]

Of course it's possible... it happens every day. When I fly from NY to Rome, I'm traveling through time. :cool:

Well, no more than you are traveling from your house to work. Or across the room. As far as I know, anyway. A time zone isn't another kind of time.

I have an awful time with Quantum Physics, that "hot and happenin'" field of modern science. I am vaguely aware that there is Space/Time and if we go slow through space and fast through time or vice versa we have the same amount of Space/Time in each case. And no doubt even that vague understanding is wrong. :(

A wonderful scifi story I read years ago addressed the Parallel Universe bit very nicely: a man one day found a Dewey dime in his change and used it for his subway fare. He got off at his usual stop and went to his house and found that he was now the happy husband of a beautiful redhead when in the morning he'd been the bored husband of a beautiful brunette. It was a good story. He saved his change in each universe and could go back and forth at will. That was about the end of the story. It was a good story, it's stayed with me for, jeez, I bet over 40 years. But time didn't seem to enter into it.

Sorry to Osgiliate the thread.

[XT]

Well, no more than you are traveling from your house to work. Or across the room. As far as I know, anyway. A time zone isn't another kind of time.

Actually, he's right...check out relativity sometime and what happens when you travel. Oh, it's a tiny effect at the speed of an air plane...but there IS an effect. Consider what happens as you approach the speed of light...and extrapolate backwards.

-XT

[vison]

Actually, he's right...check out relativity sometime and what happens when you travel. Oh, it's a tiny effect at the speed of an air plane...but there IS an effect. Consider what happens as you approach the speed of light...and extrapolate backwards.

-XT

I knew I'd be wrong!!! I knew I was wrong about the time zone thing, but it felt right to write it.

That's my excuse and I'm sticking to it.

Until I can finish inventing the Time Machine and go back and edit it away. Missed the edit window, y'see.

[Bryan Ekers]

If rapid movement causes time dilation, my personal inertia must be zooming me to the future at an alarming rate.

Whoa, intense. I better go lie down.

[Larry Borgia]

It's my understanding--and boy could I be wrong about this--that the "many worlds" hypothesis didn't merely posit other realities where Gore was president or the South won the Civil War, but posited a new Universe for every single quantum event. In other words, in the Universe Next Door, Bush is still president, the North still won, everything is exactly the same as it is in this universe, except one millisecond ago on a tiny moon in the Andromeda Galaxy, an ice outcropping emitted a photon, while in this universe it didn't. You'd have to go through 10^(some huge number)^(some even bigger number)^(some number so big it actually has mass) universes before you found one with a measurable difference from ours, like said ice outcropping weighing a milligram more than it does here.

[sciurophobic]

I'll tell you yesterday.

[vison]

It's my understanding--and boy could I be wrong about this--that the "many worlds" hypothesis didn't merely posit other realities where Gore was president or the South won the Civil War, but posited a new Universe for every single quantum event. In other words, in the Universe Next Door, Bush is still president, the North still won, everything is exactly the same as it is in this universe, except one millisecond ago on a tiny moon in the Andromeda Galaxy, an ice outcropping emitted a photon, while in this universe it didn't. You'd have to go through 10^(some huge number)^(some even bigger number)^(some number so big it actually has mass) universes before you found one with a measurable difference from ours, like said ice outcropping weighing a milligram more than it does here.

You may be wrong, but if you are, so am I. This is how it was explained to me. It renders the notion pointless, IMHO.

[Wendell Wagner]

vison writes:

> I have an awful time with Quantum Physics, that "hot and happenin'" field of
> modern science.

Quantum physics was hot and happening about ninety years ago. As I said in my post above, if someone really wants to learn about it, they should read a popular introduction to the subject (and completely ignore anything in Crichton). Nobody has suggested such books so far, so I'll give a list of such books that I found online:

Fritjof, Capra _The Tao of Physics_
Gell-Mann, Murray _The Quark and the Jaguar: Adventures in the Simple and the Complex_
Greene, Brian _The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory_
Gribbin, John _In Search of Schrödinger's Cat: Quantum Physics and Reality_
Gribbin, John _The Matter Myth: Dramatic Discoveries That Challenge Our Understanding of Physical Reality_
Hawking, Stephen _A Brief History of Time_
Kaku, Michio and Thompson, Jennifer Trainer _Beyond Einstein: The Cosmic Quest for the Theory of the Universe_
Thorne, Kip S. _Black Holes and Time Warps: Einstein's Outrageous Legacy_

I call on those more knowledgeable about the subject than I to improve this list.

[Stranger On A Train]

Nobody has suggested such books so far, so I'll give a list of such books that I found online:

Fritjof, Capra _The Tao of Physics_
Gell-Mann, Murray _The Quark and the Jaguar: Adventures in the Simple and the Complex_
Greene, Brian _The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory_
Gribbin, John _In Search of Schrödinger's Cat: Quantum Physics and Reality_
Gribbin, John _The Matter Myth: Dramatic Discoveries That Challenge Our Understanding of Physical Reality_
Hawking, Stephen _A Brief History of Time_
Kaku, Michio and Thompson, Jennifer Trainer _Beyond Einstein: The Cosmic Quest for the Theory of the Universe_
Thorne, Kip S. _Black Holes and Time Warps: Einstein's Outrageous Legacy_

I call on those more knowledgeable about the subject than I to improve this list.With due respect, I'd wastebin Capra and the Gribbin books (I haven't read the second, but In Search of Schrödinger's Cat contains a number of conceptual errors and tends to promote one interpretation of QM over others without basis). If the intent is to get an actual, if superficial, grounding in the fundamentals of modern physics, I'd start with Richard Feynman's Six Easy Pieces (http://www.amazon.com/Six-Easy-Pieces-Essentials-Explained/dp/0465023924/ref=ed_oe_p), followed by Six Not So Easy Pieces (http://www.amazon.com/Six-Not-So-Easy-Pieces-Relativity-Space-Time/dp/0465023932/ref=ed_oe_p), which are drawn from his more complete Feynman Lectures on Physics (http://www.amazon.com/Feynman-Lectures-Physics-Richard-Phillips/dp/0201021153); the first covering basic atomic physics, the concepts of energy and gravitation, and (in the last section) the fundamentals of quantum mechanics; and the second going into detail on special relativity. These are presented in a somewhat conversational manner without too much math, but will provide a much better foundation for understanding physical behavior than pop science books (especially those that attempt to tie in physics with philosophy or theology).

Stranger

[CurtC]

Nobody has suggested such books so far, so I'll give a list of such books that I found online:

Fritjof, Capra _The Tao of Physics_

Yes, that is a book, and I'm sure you found it online. I made the mistake of reading it back in the mid 1980s, and I want that couple of weeks of my life back. That book is rubbish.

It basically makes the point that Quantum Mechanics is weird, and eastern philosophies are weird, therefore the ancient orient philosophers seemed to know about the Truth of the universe that "Western" science is only just now uncovering.

Pure rubbish.

[vison]

I've read 2 of those books: Brian Greene's and Stephen Hawking's. I thought Greene's was easier to understand. Somewhere I have the Feynman book Six Easy Pieces, but I confess I was a bit intimidated when I began it. I'll dig it out and try it again.

Thanks for the list, Wendell Wagner.

[Stranger On A Train]

I've read 2 of those books: Brian Greene's and Stephen Hawking's. I thought Greene's was easier to understand. Somewhere I have the Feynman book Six Easy Pieces, but I confess I was a bit intimidated when I began it. I'll dig it out and try it again.Understand that Feynman isn't (for the most part) a science popularizer, per se; Six Easy Pieces come from his now-famous lectures (compiled and put in published form by Robert Leighton and Matthew Sands) which were intended as an attempt to present a basic foundation on physics from classical mechanics through modern physics (quantum mechanics, statistical mechanics, relativity) for an undergraduate audience. As such, he introduces concepts, and then moves into more rigorous mathematical descriptions. Like any classwork they require some study to ingest, but the basics, especially in Six Easy Pieces are pretty simple.

Of the science popularizers listed above, my favorite is Greene (despite his overarching obsession with Simpsons metaphors he stays pretty grounded, and qualifies his speculations when he does get away from accepted and tested theory), but if you approach the topic without starting out from a grounding in basic physics, it becomes kind of mystical nonsense rather than just a shift in thinking. To understand why relativity and QM are so revolutionary, you first need to understand the classical view of how things work and why the discovery that, on scales outside of normal experience, they don't actually work that way is so extraordinary.

Stranger

[Anne Neville]

It's getting increasingly unlikely that I, personally, will ever get hold of a time machine. I tend to get upset when forced to deal with uncertainty. If I got a time machine, I would go back to uncertain times in my past (like when I had applied to colleges and was worried about where I would get in) and tell my past self how things turned out, especially if they turned out OK. I would have told my past self that she would get into the University of Maryland, and do well there, for example. That hasn't happened, so...

Of course, it's possible that I just happen to be the version of myself in the universe that no time travelling version of myself managed to get to. I do rather like the parallel worlds interpretation of quantum mechanics.

It's also possible that I will eventually become convinced that being upset about uncertainty was somehow good for me, so I shouldn't go back and tell myself how things turned out. Unlikely- I deeply believe that the whole "suffering builds character" idea is absolute rubbish. Even if it weren't, I'd rather not suffer and have a weaker character, given the choice.

[Wendell Wagner]

CurtC writes:

> Yes, that is a book, and I'm sure you found it online. I made the mistake of
> reading it back in the mid 1980s, and I want that couple of weeks of my life
> back. That book is rubbish.

Thanks for the warning. Could you now recommend some good introductory books about quantum physics? As you may notice, I asked people more knowledgeable about quantum physics than I to recommend some books back in post #16. I waited two days, but no one posted any recommendations, so I grabbed a list from a website on quantum physics. In any case, it's better to read any of those books than some Michael Crichton novels, which are utter junk scientifically.

[ralph124c]

Backwards time travel violates causuality, so it is very likely impossible. Forward time travel is indeed possible, but owing to the huge amount of energy necessary, will also be impossible. I would propose a third idea:if space-time is indeed a continuum, then there ought to be some way to communicate along world lines-such that the likelyhood of future events could be predicted.
unfortunately, i don'y know how information could be transmitted along a world line.
that is for next week (stay tuned)

[Contrapuntal]

Let me get back to you.Brilliant.

[NineToTheSky]

I also enjoy Brian Greene. He goes to enormous lengths to get you to understand what he's trying to explain, and his enthusiasm just carries you along. I would also recommend The Fabric of the Cosmos by him.

Marcus Chown is also very readable: in particular, Quantum Theory Cannot Hurt You.

While I am sure that Stranger is correct, as a beginner, I find Richard Feynman a little too difficult. I am working my way up to him. :)

I find Stephen Hawkins a little dry, and I am puzzled by the amount of time he brings God into the equation. I'm not sure if he believes in him or not.