Physicists investigate how time moves forward
September 5, 2008 By Lisa ZygaAs humans, we have a very intuitive concept of time, and of the differences between the past, present, and future. But, as scientists Edward Feng of the University of California, Berkeley, and Gavin Crooks of the Lawrence Berkeley National Laboratory point out, science does not provide a clear definition of time.
“In our everyday lives we have the sense that time flows inexorably from the past into the future; water flows downhill; mountains erode; we are born, grow old, and die; we anticipate the future but remember the past,” the scientists write in a recent study in Physical Review Letters. “Yet almost all of the fundamental theories of physics – classical mechanics, electrodynamics, quantum mechanics, general relativity, and so on – are symmetric with respect to time reversal.
“The only fundamental theory that picks out a preferred direction of time is the second law of thermodynamics, which asserts that the entropy of the Universe increases as time flows toward the future. This provides an orientation, or arrow of time, and it is generally believed that all other time asymmetries, such as our sense that future and past are different, are a direct consequence of this thermodynamic arrow.”
In their study, Feng and Crooks have developed a method to accurately measure “time asymmetry” (which refers to our intuitive concept of time, that the past differs from the future, in contrast with time symmetry, where there is no distinction between past and future). They began by investigating the increase in energy dissipation, or entropy, in various arrangements.
The scientists’ method of measuring time asymmetry is best explained in the context of an experiment. In the macroscopic world, where glasses of milk are spilled, time asymmetry is obvious. But on the microscopic scale, because the amount of energy involved is so small, it’s more difficult to tell that entropy is increasing, and that time is moving forward and not backward. In fact, during some intervals, entropy might actually decrease. So even though overall entropy is still increasing on average, in accordance with the second law, the direction of time is not obvious at every moment in the experiment. Further, the scientists show that even an average entropy increase does not necessarily ensure time asymmetry, but can arise in an arrangement that appears time-symmetric.
Feng and Crooks wanted their new measurement method to explain how time can move forward even at points when entropy is decreasing. To do this, they analyzed the folding and unfolding of a single RNA molecule attached to two tiny beads. By controlling the distance between one bead and an adjacent optical laser trap, the scientists could stretch and compress the RNA molecule. Initially, the RNA starts in thermal equilibrium, but, as it’s alternately stretched and compressed, the total entropy of the RNA and the surrounding bath increases on average.
“We use an ensemble, or large number, of RNA trajectories to measure the time asymmetry,” Feng explained to PhysOrg.com. “Using work measurements for both forward and reverse experiments, we simply plug these measurements into an expression for A, or time asymmetry, in the paper. Assuming we know the free energy change, this gives the square of the length of time's arrow.”
To measure time asymmetry in this arrangement, an observer watching the RNA’s trajectory of unfolding and folding should be able to tell if the trajectory was generated by stretching or compressing. The scientists quantify this observation in terms of the “Jensen-Shannon divergence,” a probability which gives a “0” if stretching and compressing are identical, a “1” if they are distinguishable at every moment, and some fraction of one if they overlap occasionally.
This probability, Feng and Crooks explain, can more accurately describe time asymmetry than a simple measurement of average entropy, since the average entropy is sensitive to unusual events. For example, if the RNA becomes tangled, it resists being unfolded when the beads expand. Because the tangled RNA is pulled apart very slowly, the process is essentially time-symmetric. The scientists show that a model of this process has large average dissipation, or entropy increase, but small time asymmetry, as one intuitively expects due to the slow pulling.
“The Jensen-Shannon divergence is better than the average dissipation due to its mathematical form,” Feng said. “This accounts for the rare events in a different way, which we show with the RNA molecule that can get stuck.”
Besides the theoretical interest, this research could have other applications, such as for estimating free energy differences in non-equilibrium experiments. The scientists explain that understanding the relation between time asymmetry and entropy could also be important for studying molecular motors and other kinds of biological machinery.
“While time blatantly moves forward in the macroscopic world, the direction of time becomes confusing on the scale of a single molecule,” Feng summarized. “Our definition employing the Jensen-Shannon divergence highlights this distinction. We hope this will have an impact as scientists study biological molecules and continue to perform single-molecule experiments.”
More information: Feng, Edward H. and Crooks, Gavin E. “Length of Time’s Arrow.” Physical Review Letters 101, 090602 (2008).
Copyright 2008 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.
Sep 10, 2009 |
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We regard the reality in which we have mental access to, subjective phenomenal reality, as opposed to noumenal reality, ... this reality is forever entangled with, and tainted by mental constructs and modes of understanding, the result of which are conceptual artifacts like 'time'.
I somewhat agree with you and in other manners I disagree. Time does appear to be relative but there are processes that define time and are defined by time such as gravitation and the bonding of time with space in regard to velocity and acceleration.
I do understand where you're comming from though and you could be completely correct, I'm just not so sure it's that clear cut.
Exactly.. Time is a conception we made up as we observe Systems moving energy from one high state to another. (Such as a clock 'unwinding')
I bet if we re-wrote time as a concept of energy flow instead of its own entity, a lot of equations will solve and fall into our lap.
Very well worded. I believe you are correct in your assessment that time, as we experience it on a day-to-day basis, is probably an artefact defined completely by our limited understanding of the reality which underlies our world. However, I would be curious in regards to your thoughts about extra dimensions of time, as some theoretical explanations of our universe are purported to require.
enslaved by "cause and effect". We choose some basic cause and effect and compare others. "Rate"
of a chosen cause and effect is compared to others. "Time" stops with the chosen standard.
I don't know what you mean by 'holographic theory of self', ..really its more a matter of epistemology. Reality, [i]as it is[/i], ...noumenal reality, ...cannot be reproduced within the confines of a bio-mechanical mind; ...to 'fit', it must conform to conditions inherent within mind, given minds operating nature,.. in other words, understood within a-priori conceptual paradigms, time, etc.
To have knowledge of reality, implies that the mind has encapsulated it within the scope of its pre-existing intellectual forms and logical relations (space, causality, time, etc). None of these are discoverable in themselves apart from their mental application.
The holographic theory of self is a very complex ideology but the basic tennants are that reality exists as it does because we perceive it to be so. In reality, there are no physical laws that aren't imposed upon us by our observational awareness.
It sounds kinda loopy from a scientific perspective but it has some correlation with the so called "odd" behavior of quantum mechanics.
We can't get out of our own intellectual way, ...so it appears that these things have infused in themselves a 'real' component of time, but we are the ones doing the defining, the ones obtaining the knowledge of these processes, ... the form of this knowledge is predetermined given the minds 'design'.
Ok, I wasn't aware of that. From my perspective I would reference Kant's Critique, I believe he discovered something, though entirely useless as it doesn't change anything, except that phenomenal reality (reality as it theoretically could be subjectively understood), might not be all there is.
Yes, the 'odd' behavior of QM, i'm sure reality is not odd to itself,.. only to us in trying to obtain knowledge of it in terms necessary for a macroscopically evolved mind. For example, 'there is no' wave function collapse as an entity in itself, ...reality is whatever it is, until it is made to conform to conditions of understanding, the 'observation' is an odd shaped box.
In my opinion the universe is strange kind of circuit, I've been studying some interesting ideas of William James Sidis - The animate and inanimate, and he conceived the concept of the "reverse universe", and I thought, hey that sounds like an electronic circuit.
If we interpreted many phenomena in the universe in similar terms of electronic and their components (i.e. black holes, etc), I bet we'd be doing a lot better. Nature appears to be a self-repeating fractally recursive structure.
On the contrary, time is very intrinsic in the objective reality itself (the one accessible by way of experiments - the only one science is interested in), 2nd law of thermodynamics is pretty damn solid and in the macro world there is absolutely no ambiguity as to which way the time is going and no room for it to be tainted by our mental constructs.
And if you want to argue on the more counterproductive philosophical level where objective reality is inaccessible - to know that something is an artifact of our mental constructs you would have to have access to the objective reality itself, which you don't.
You could argue that everything is such an artifact, but then the statement loses all its descriptive power.
Entropy is a concept which requires a mass of elements, gas particles, whatever,.. but time is lost somehow in this system if you expect to find it, rather than apply it. Examine a single element of this system alone and as the point of the article, it becomes a problem.
But, in order for the second law of thermodynamics to be correct it relies on time being held as an inviolate constant, which there is no scientific basis for outside of the second law of thermodynamics.
By AWT the time is asymetric, because it's formed by density gradient of Aether. In analogy of space-time with water surface, the space dimension is the direction paralell with water surface, while the time is the direction normal to this surface gradient - as such it's always oriented. http://superstrun...sion.gif
Now we can understand better the (mem)braneworld concept of string theory, too.
Its not a "mental ordering of phenomenon" cause that ordering is constantly being preserved in the reality itself most importantly in its spatial relations.
Turn on a camera and it will record events, their spatial relations on film prove that this ordering is a part of reality and not a product of human mind.
It does not rely on time being held as an inviolate constant, time can change freely, what matters is that at the later point in time the total entropy of a closed system (and Universe as a whole) will be higher so by calculating entropy we can find out the time order of macroscopic events.
But right there you used "time" to define the law. It's a required entitiy for the second law to work.
Here's a thought experiment for you: Imagine a universe where there was exactly ONE object. It would thereby be impossible to experience time because time is essentially a spatial rate of change and there would be nothing to measure against. Does time still exist, or does the effect only exist as it is observed, in order to explain the spatial changes themselves?
Yes, but it doesn't have to be constant also the law only defines the direction of time flow - time arrow, not what time is.
Universe is a 4d spacetime (or at least thats our best model to date) so time would still be there if I tried to imagine a universe just as there would be space, even if said universe were to be completely empty.
If anything is an artifact of human mind its the fact that we only see one instance of time dimension and therefore can only define time as a "measure of change", but that doesn't make time any less real or a product of human mind.
Agreed. That scenario is much like Newton's problem of ether. If you were in the universe with nothing else and you were set to spin.
How would you know you were spinning? Would your perceptions know you're spinning but ignore it due to your frame of reference? Do you spin at all since there is nothing for you to be "spinning" in reference to.
The AWT has no problem with Mach's principle, as every object is always spinning with respect of Aether environment, which couldn't be always detectable easily, due it's immense mass/energy density. Even at water surface the underwater motion cannot be easily detectable and nothing strange is about it. It still doesn't mean, such underwater doesn't exist, as it forms a reference frame toward rotation.
The perception of the speed at which all this takes place can seem different though, if you remember back to your days as very young children when a day lasted forever, the mind was young and open to many more perceptions than a mature 'mind'.
One other thing to think about is that speed at which everything appears to take place differs depending on ones place in the universe, i.e the day of a human seems short compared to the day of the earth itself which could be millions of years. The day for a single bacteria seems very short compared to our day.
With this in mind think about how the earth would appear for a second of its time. The path its on through its 3D space and the amount of activity that would take place on the surface over that period. In the blink of an earthy eye a human would live a life time.
Of course you would be spinning. The fact that you can't prove it to yourself does not detract from the fact that you are. In other words, you would not be able to perceive it, but it would still be happening. In addition, establishing a frame of reference under these circumstances is impossible because there is nothing relative to yourself upon which you could base it.
What "flows" with respect to time is the coming into existence of more and more observable states of the universe. The past consists of all states that have come into existence. For time to "reverse" would mean that more and more past states would cease to have ever existed, which to me seems a logical contradiction. What makes time different from spatial dimensions is that all locations of the spatial dimension exist together, whereas only past points of time have actual existence.
For events to violate the second law of thermodynamics would not be a reversal of time, it would simply mean that new states would be coming into existence where the change from one state to the next would be different than what is allowed by the second law. Suppose an egg is cracked open and fried, and the egg "unfries" and reassembles itself. That sequence of events, if observed, would not be a reversal of time, it would be a repetition of events in forward and then reverse order, not a reversal of time itself. For time to reverse would mean that the fried state of the egg would cease to have ever existed and ever to have been observed. When I watch a movie that depicts something of this sort, I do not have a sense that the "arrow of time" has turned backwards, I simply have a sense that something is being depicted that is the reverse of what is normal or even possible.
The reason that we can say that most "fundamental theories of physics" are time reversible is that we can conceptually lay out a time line of events that is not dependent upon the events actually having occurred, rather is only dependent upon the possibility that they could occur.
It does occur to me that if it were logically possible for time to actually reverse (i.e., for past states to cease to have existed), then the one "fundamental theory of physics" that would come into play would be the indeterminacy of quantum theory. What would happen if time truly reversed and then turned forward again is that the new sequence of states that would come into existence would not exactly duplicate the previous sequence whose existence had been erased.
Imagine an oscillator of a macro sized spring and a mass as we know it from lab. With Hooke's law and some math, we can find an expression for the first eigen frequency of the system. Now imagine that we go smaller and smaller. Imagine that when arriving at nanoscale the system starts perceiving time differently.
Maybe because internal molecular vibrations of the system becomes obvious for the system itself. As a result time starts to contract depending on the energy present in the system. The energy continuously changes as a result of interaction with neighboring particles, so the time perception of the nanosystem as a function of our time conception becomes a chaotic mess. Maybe while you were observing the behavior of the nanosystem, years have gone by for that system or while you were watching the system for a year, the system perceived only a ms.
Odd behaviour of the nano system like frequency responses can give clues about this:)
Someone here has given the blind bats example, as for them space would be like time to us. I completely disagree: Even blind bats can "see" objects and space using it's sonar. They have an acoustic vision, very similar to our light vision.
Anyway, I'm pretty much convinced that the key to understand our universe it's motion.
If you give that some serious thought, everything in our universe (including us) moves at near light speeds.
Therefore, I think that all fundamental forces of nature (nuclear strong; nuclear weak; gravity and electromagnetism) have their origin in some kind of motion.
From this point of view, the time exists by the same way, like the electron cathegory exists, because we can postulate the existence of different space-times with common metric and the number of time dimensions. By AWT the time is the flatness of space-time, i.e. the density gradient, which is serving for causual energy spreading in transversal waves.
http://superstrun...evol.gif
If some prism can be more flat, then the cube, then its flateness objectivelly exists as a geometrical cathegory. After all, we can estimate a number of time dimensions, by the same way, like any other quantities. If we can measure something by reproducible way, it exists, at least as a cathegory concept.
But for time to reverse, wouldn't the original sequence of events have to have taken place, otherwise where would it be reversing from?
Wouldn't it make more sense to say that if one reversed time, the point at which we emerged would be the start of a new timeline and by default a new universe to contain it, since that original timeline would still need to exist, but logically not in the same 'place' as the new one?
No, the bat is sensing changes in its flow of consciousness. When the bat is not flying he is not sending out waves and he senses a certain flow of consciousness then he produces a sound and the wave is returned from the wall and it's detected, then the normal flow of consciousness continues until another wave is returned. So it is not time the bat is sensing it is changes in the flow of his consciousness (whatever that is for a bat).
Of course, the impossibility of movement in spacetime is not something that one hears too often because it makes a lot of famous people look rather foolish. However it is the reason that Sir Karl Popper wrote in his Conjectures and Refutations that spacetime is Einstein's block universe in which nothing happens. It is also the reason that relativist Dr. Robert Geroch wrote in Relativity from A to B, "There is no dynamics within space-time itself: nothing ever moves therein; nothing happens; nothing changes. [...] In particular, one does not think of particles as "moving through" space-time, or as "following along" their world-lines. Click on the link below for more on this topic:
Nasty Little Truth About Spacetime Physics
http://www.rebels...ious.htm
The space-time motion in relativity sense is defined by radiative time arrow, i.e. by spreading of information by luminal speed. With respect to radiative time arrow definition the motion through space-time has a deep meaning, or all these formulas for time dilatation are wrong.
Can you propose some alternative for explanation of experimentally verified changes of pion decay rates during motion of high speed? No? After then just keep the relativity it's geodesics and space-time motion concepts.
Yes. There is only one time definition used in relativity. It's the same one used by Newton. Time is that which is measured by a clock, as per Einstein. As far as so-called "time dilation" is concerned, clocks slow down (or speed up) for the same reason that every physical phenomenon occurs: conservation of energy. Besides, it's not as if relativity explains why clocks slow down. They just observe it and put the moronic "time dilation" on it. Time cannot change, by definition. Change exists and time (temporal interval) is abstractly derived from it. Deny at your own detriment.
All the time travel nonsense we hear from famous physcists like Stephen Hawking, Kip Thorne and others is pure crackpottery. It tells me they don't understand the very theory they are supposed to be experts in, among other things. The result is that I have very little respect for spacetime physicists.
You fail to understand some very basic things about science (though maybe not so obvious):
1. All definitions used by science are created by science and science can change them when such change is warranted.
2. Science is interested in finding the simplest and most useful explanation, not the one which best agrees with our common sense or the one that agrees with our present definitions - the one which has the most predictive power and least assumptions.
Heres an example of what it means:
Suppose we have a giant model of reality which correctly explains 60 000/100 000 physical phenomena. We try to develop it to explain more.
After some work we find out that by changing the concept of time (throwing out an absolute time) we can improve our model so that it will predict another 20 000 phenomena correctly.
We will happily make such change, even if the new definition of time is far less intuitive and harder to understand.
We will make it cause if it explains more phenomena it means it is closer to the way Nature really operates and understanding Nature is the ultimate goal of science.
We will also make it cause it has superior predictive power which will allow us to both make farther progress in science and to develop new technology.
General relativity is an example of just such situation, to gain more insight into reality the concept of time has been redefined and the spacetime was born.
Thats why arguing that time is not a variable and cannot change cause that is its definition is a misunderstanding on your side - science does not use your definition, science treats time as a dimension (either whole dimension or as a single point in it depending on context), something very similar to space dimensions. Scientific time is relative and flows with different rates in different situations.
You are of course free to use your own definition of time but attacking science based on it is rather silly.
http://superstrun...evol.gif
By another words, the existence of time follows from asymmetry of energy spreading in Aether: at the moment, the energy will start to prefer the surface of some gradient, it
establishes the time and space dimensions for its spreading, too.
http://superstrun...sity.gif
Please note, that the formation of gradients in higher dimensions implies the formation of time dimension pairs, because the bubbles of resulting foam are formed by two surface gradients. These two gradients aren't completelly equivalent though and this asymmetry corresponds the violation of matter and antimatter symmetry (so called the "CP symmetry breaking").
http://www.physor...669.html
http://www.physor...776.html
and anti-universe.
Our universe is in a constant flux at a set frequency. That frequency is about
137,036,000,000 oscillations per second. which is related to the Fine Structure Constant. Time
Stress is a term used when talking about the percent of potential difference of total time present
in a field force. Its like talking about the potential difference in a electric circuit. Total time =
100% of the forward and 100% of the backward cycle. Each side is represented as a whole
100%. Most of the universe operates on a stress of 3% or less. That is 3% of total time and is
true on both sides of the cycle. (Figure 3) That 3% includes most electron interaction at shell
distance from the nucleus. All chemical bonding. Normal gravity (Anything that won't crush you) and sex.
Due to the design of the universe and ourselves, we are only aware of time passing in
universe, and we call this arrow, forward time. There is no bias for forward time, time and anti-
time are of equal overall duration.
Filter Mechanics theory
David C Beach
So claiming that you are finding out about time by measuring it with matter is sort an oxymoron..
Now that is not to say that you cannot slow process down as evidenced by slow light. You might even be able to time travel because everything exists at one moment in time.
If you have the "ability" you can see all events at once..
Soounds crazy, doesnt it?
Thus one viewpoint to another will always have their own view as their position of observation is normally not in the same space as another (another law of this universe - two objects can not occupy the same space, unless you become identified as that object. Not true of spirits, ghosts or life-force whose physical universe laws don't apply.)