Time’s Arrow One of the discrepancies between the classical world and the quantum world is how our world is governed by the passage of time, which only flows in one direction, from the past to the future. When watching videos in the olden days, if you accidentally hit rewind instead of fast forward, it would only take a second to realize your mistake. A barista walking backwards only to see the coffee flowing up from a cup into his pot; or an animal being unborn in a wildlife documentary; these things look inherently odd and impossible to us because they suggest that time is in fact reversed. However, microscopic processes are time symmetric—collisions between atoms or chemical reactions—can occur backwards or forwards. So any quest to understand emergence must also include trying to understand how these seemingly contradictory processes can be matched. From article: http://www.fqxi.org/community/articles/display/197
Nothing in our world is governed by "the passage of time". Time doesn't flow. That's just a figure of speech. Things move and interact, that's all. The arrow of time doesn't literally point towards the future. It isn't a real direction, nor is the direction of a chemical reaction. And it isn't really true that microscopic processes are time-symmetric. Steel turns to rust. You've seen that plenty of times. But you don't often see rust turning into steel. Alternatively hydrogen fusion occurs in stars, then other elements undergo fusion and you end up with iron. But you don't see iron being converted back into hydrogen.
I think it's a bit silly to say the "quantum world" is not governed by the passage of time. After all, spontaneous processes at the atomic scale lead to increase in entropy, which is unidirectional. So it is untrue to suggest that at the "quantum scale" everything is reversible and there is no direction to time. The argument about whether "passage of time" is the right term to describe the difference in time between an earlier event and a later one strikes me as purely semantic.
Spellbound is on his 5th or 6th definition of reality. I guess it is fair to say that spellbound does not have a very firm grasp on reality.
Semantic is to do with meaning. That sort of thing is important to physicists. Once you appreciate that time doesn't flow, you appreciate that an optical clock goes slower when it's lower because light goes slower when its lower. After that you read what Einstein said, and you understand gravity, and that it is not entropic. One thing leads to another.
What I meant is that the expression "passage of time" is an age-old literary expression, conveying the everyday experience that things such as the movement of the sun in the sky or the ticking of the second hand on a clock indicate the order of a sequence of observations or events. There is nothing in the expression "passage of time" that contradicts anything in relativity, for the simple reason that it is not intended to be a scientific description.
OK noted. But do note that people have a bad habit of taking such literary expressions literally. If you started a thread on the science forum asking What Does a Clock Do? chances are you'll be told it measures the flow of proper time. If you were to challenge that and point out that a clock features some kind of cyclical local motion that is counted and displayed as "the time", you will find yourself getting into bother. It might be interesting if you gave this a whirl.
Well, the imagery of "flow" is again literary of course. But it is natural that people use such imagery, since you cannot see time: you can only see objects moving over a period of time, so that is the way it gets visualised. And we also talk of future events "approaching" or past events "receding". This is natural and not wrong, since everybody knows what we mean by that is not movement in space, but the diminishing or increasing in intervals of time between the present of the observer and the event in question. Frankly I think some physicists and philosophers get their knickers needlessly in a twist over this. I have yet to encounter any misapprehension of physics that arises from talking of the passage of time. In this respect it seems to me unlike, say, the confusion that can arise from muddling up mass and weight in Newtonian mechanics.
Actually, you can see objects moving. That "period of time" is something you determine from your clock, which features something else moving. IMHO there's a lot of "natural" expressions that cause big issues. When people have grown up with some figure of speech, they have great difficulty being scientific and rational about it, and examining whether it actually matches experience. I think there's massive misapprehension, leading to things like belief in the possibility of time travel. Not to mention issues with the speed of light, gravity, black holes, and inflation. But of course, persuading people to examine these issues is not always easy. I think it's much much worse.
I do not disagree that there are misapprehensions about the way time is treated in physics, especially when it comes relativity. But I do not see that any of this can really be laid at the door of the concept of time passing. Nothing in that idea says it has to pass at the same rate for all observers for example. As for time travel, the problems with that are nothing to do with physics: they are far more obvious, to do with causality, i.e. the logic of going back into the past and killing your father etc. No, I think starting an attack on the concept of time passing is a dead end: a sure way to confuse laypeople needlessly - and make some of them think you are far too much up your own arse.
The grandfather paradox is a nonsense because time is a measure of local motion. It isn't something we move or travel through. We don't travel forward in time, so the notion of travelling backwards through time is a total fantasy. Which means the chronology protection conjecture is a futile notion from somebody who doesn't understand time. As I said, some people have great difficulty being scientific and rational about this sort of thing. When you challenge a conviction that they can't defend, they react with automatic abuse. It's like Morton's demon. It's like the shutters are down and there's nobody home.
If something moves from point A to point B, we think of its time of arrival at point B as being later than the time it left point A. It never arrives earlier than it left. The temporal distance between me and last Thursday seems to increase steadily at a rate of one day per day. I seem to be approaching my next payday at the same inexorable rate. Time assymmetry seems to me to be closely associated with the fact that physical causation appears to propagate in one preferred temporal direction, namely from the past towards the future. The past seems to be what determines the future (to whatever extent determinism is true) rather than the future determining the past. It's true that a great deal of the mathematical apparatus of physics does seem to be time symmetric. The formalism would seem to be consistent with physical systems evolving in both temporal directions. Entropy seems to be one of the exceptions.
Of course it is. How else can we get from one place to another? Time travel is demonstrated mathematically by the existence of closed time-like curves.
Time asymmetry in the quantum realm might be interesting, and I can't say if the "spooky" action of QM holds some trick of nature that puts events out of order somehow. Still, who is to say what the proper order was of those events in Reality. I prefer the concept that time simply passes. If you have one clock you might think you know what time it is, but if you have two, you are never really sure Please Register or Log in to view the hidden image!. It is the measurement of time that seems to be at issue, and that varies for clocks in relative motion, (or higher or lower as Farsight says).
Bollocks! Time travel is certainly not forbidden by the laws of physics and GR, and in fact the equations of GR give solutions as to how it can be achieved by any sufficiently advanced civilisation. Forward time travel is relatively easy, although backwards time travel could create logical problems and inconsistencies. Although solutions to these have also been forthcoming. You have yet to challenge what I have claimed.... You offer unsupported conjecture that most physicists disagree with. Couple that to the fact that you are just a rank amateur like myself, and a delusional one to boot, and your claims and statements can be viewed with the contempt they deserve. And I havn't even mentioned about your claim about having a TOE and having rewritten 20th/21st century physics!
Spellbound #1 It's not a discrepancy if the subjective idea of "time" as a regulating or causal phenomenon is removed. After much debate and theorizing, on the subject of "time", there is still no tangible evidence, no "time in a bottle". Time is a number, a magnitude without direction, which eliminates the "arrow" analogy. At the quantum scale, particles can assume different states, which we label A, B, and C. When a particle transforms from A to B, and later from B to A, the lab clock accumulates time in both cases, and does not run backward for the 2nd case. It's just a case of a reversed sequence. Available energy is more likely the determining factor for particle transformations. Compare the coin toss of HHHT and THHH. The probability for either sequence is equal, and constant, therefore independent of time. All phenomena are not deterministic or predictable, which makes some people uneasy. Consider a motionless glass on a table top. In the context of thermal energy, it's possible for all the molecules to acquire the same velocity for a brief period, and the glass to spontaneously move along the top surface. Considering the dynamics involved at that scale, the motion would go undetected, and the glass would appear to remain in place. The glass would be many orders of magnitude more complex than a fundamental particle. If the glass was intentionally pushed off the table and shattered on the floor, the glass has gained in complexity. If the probability of detecting spontaneous motion of an object like a glass is not significantly different from zero, then the expectation of a shattered glass reassembling itself as it returns to the table top is zero. It's not time, but complexity of the structure being examined that determines the reverse process. exchemist #3 Gravitational fields add energy to objects moving in them, and form orderly systems of objects like galaxies. Genetic code forms complex plants and organisms from the elements. Unless these phenomena are removed, the universe will not experience the entropy related "heat death".
In brief: The laws of physics allow members of an exceedingly advanced civilisation to travel forward in time as fast as they might wish. Backward time travel is another matter; we do not know whether it is allowed by the laws of physics, and the answer is likely controlled by a set of physical laws that we do not yet understand at all well: the laws of quantum gravity. In order for humans to travel forward in time very rapidly, or backward (if allowed at all), we would need technology far far beyond anything we are capable of today. http://plus.maths.org/content/time-travel-allowed. http://www.pbs.org/wgbh/nova/physics/Sagan-Time-Travel.html "Time travel into the indefinite future is consistent with the laws of nature." http://www.preposterousuniverse.com/blog/2013/10/18/is-time-real/
From which you assume Arthur Eddington's "entropy is the arrow of time". I (and many others) regard this as problematic It is not true to say that entropy always increases incrementally, rather one would say that a closed, undisturbed system has an overwhelmingly greater probability of progressing from a state of low entropy to one of higher entropy This is TDII as I was taught it Would you (or anyone else) be comfortable with the assertion that time "goes in the forward direction with a high degree of probability"?
entropy, in some scenarios, is wasted energy, needing to go somewhere, usually said to another dimensional plane/ parallel universe.
