Time's Arrow debate

Some physicists claim that time appearing to be the ultimate form of progress is just an illusion.
Here's interesting debate featuring Jim Al-Khalili, Craig Bourne, Angie Hobbs, Raymond Tallis:
http://iai.tv/video/time-s-arrow
What do you think? Are different accounts of time needed?

 

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http://arxiv.org/pdf/1203.6440v2.pdf

Fractal-Flows and Time’s Arrow
Leonard Susskind

Abstract
This is the written version of a lecture at the KITP workshop on Bits, Branes, and Black Holes. In it I describe work with D. Harlow, S. Shenker, D. Stanford which explains how the tree-like structure of eternal inflation, together with the existence of terminal vacua, leads to an arrow-of-time. Conformal symmetry of the dS/CFT type is inconsistent with an arrow-of-time and must be broken. The presence in the landscape of terminal vacua leads to a new kind of attractor called a fractal-flow, which both breaks conformal symmetry, and creates a directional time-asymmetry. This can be seen from both the local or causal-patch viewpoint, and also from the global or multiversal viewpoint. The resulting picture is consistent with the view recently expressed by Bousso. In the last part of the lecture I illustrate how the tree-model can be useful in explaining the value of the cosmological constant, and the cosmic coincidence problem. The mechanisms are not new but the description is.

 

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And an old favourite of mine with Sean Carroll.
http://www.preposterousuniverse.com/blog/2013/10/18/is-time-real/

 

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A "formal debate" should be done in the "formal debate" area threads provided for that purpose in sciforums.

Forget about time's arrow for a moment. Let's talk about time dilation, a topic familiar to anyone who understands relativity.

At sea level on the surface of the Earth, time dilation is equivalent to what it would be for a projectile accelerating at 9.8 meters per second per second in a direction away from the center of the Earth.

For an object one meter above the surface of the Earth, time dilation is less than at the surface, and there is a corresponding and measurable drop in the acceleration due to gravity.

Now let's take a walk around the equator. For every step you take, the acceleration due to gravity changes direction to track the center of mass of the Earth, and time dilation changes incrementally along with it. Time dilation also changes with the tides caused by the Sun and the Moon, as well as any mass concentrations, and also the movement of the Earth in its orbit around the Sun, and the Sun around the galaxy, and our galaxy as it falls into Andromeda.

Conclusion: time does not proceed at the same RATE anywhere there is relative motion or a gravitating body. The rate at which time proceeds is different everywhere. Now, what about its arrow?

Time's arrow means, among other things, that the direction of bulk propagation of a photon or a projectile will not spontaneously reverse its path if it is moving, or that bound energy will not spontaneously decay or begin propagating if it is at rest. Hence time's arrow is intimately involved with inertia.

The Higgs mechanism gives some particles inertial mass, and those particles impart inertial mass back to the Higgs. 125 GeV of inertial mass.

Connect the dots and draw your own conclusions. Time is intimately involved with much more than the bulk propagation of energy or matter, well beyond its use in simple relativity theory. It extends to the physics of inertia and bound energy and how energy becomes bound.

Time is a matter of physics, not philosophy.

Peter Lynds has pointed out the folly of equivocating an interval of time with an instant of time. Don't make that mistake in physics. For one thing, it robs energy exchange events of all inertia. You see the problem with that, don't you?

Quantum entanglement is now routinely used for communication and it appears that this is instant. Even though it takes no time for entangled pairs to communicate states with each other, this process need involve no bulk transport of matter or energy. The instant of "now" is the instant of entanglement, and is the same everywhere. The Higgs field is entangled everywhere. Connect the dots and draw your own conclusion about whether or not this more fully explains time's arrow.

I don't see anything to "debate" with anyone on the subject of time who is paying attention. Sean Carroll evidently isn't. I read his book "From Eternity to Here", and decided he was clueless, even though I really liked "The Particle at the End of the Universe."

 

As interested layman I have a few questions.

a) Is the "fractal flow" (mentioned earlier) similar to De Broglie-Bohm's, *Pilot Wave*?
https://en.wikipedia.org/wiki/De_Broglie–Bohm_theory

b) is the *fractal flow* the basis for CDT (causal dynamical triangulation)
https://en.wikipedia.org/wiki/Causal_dynamical_triangulation

c) Is it possible that *time* does not exist independent of *change*, but emerges as a countable measurement of the *duration* of change?
I base this on my intuitive feeling that time itself cannot be measured without association to an event or series of events (change).

d) If time emerges as a by-product, would that explain it's forward arrow and the inability to "go back in time", because any physical change in any direction always produces a forward arrow of emerging time as a result of that change?

 

"Going back in time" would mean that matter and energy events halt and proceed backwards at different rates everywhere. Things that fell would levitate and reverse direction of gravity. Ultimately the Earth would revert to an aggregation of interstellar dust.

Particles of bound energy that is matter would revert and self-annhialate into unbound energy and the universe reverts to a high energy state it was in right after the Big Bang.

Inflation switches into reverse "deflation", and goes back to whatever initial conditions existed to start forming our present universe. And so what fantasy science is it that believes it is possible to "go back in time?"

Calculate just the probability of that happening. I get zero.

This is the same probability I get when I calculate the probability that propagation of bulk mass or energy will ever exceed the speed of light in a vacuum, or that 2+2=17 1/2.

 

There are different accounts of the direction of time based on things like entropy, causation, cosmology and quantum mechanics.

I guess that generally speaking, physical laws are time-invariant. In other words, they continue to apply if we run the film of the same physical event forwards and backwards. So the problem of deriving the past => future direction of time (time's arrow) from physical principles arises.

It seems that entropy is one of the small number of basic physical principles that doesn't work equally well both ways and is time assymmetrical. If I smash a bottle on the floor, that process is inherently more likely than a bunch of glass shards jumping off the floor and fusing into a bottle in my hand. So it seems like most of the physical speculation about the direction of time has sought the answer in thermodynamics.

Another possibility is the so-called 'collapse of the wave function' hypothesized by the Copenhagen interpretation of quantum mechanics. While the evolution of the Schroedinger equation is time invariant (the same whether time runs forwards or backwards), the collapse of the wave function would seem to create a time assymmetry, with superimposed possibility states in the future direction and a concrete actuality in the past direction. That idea conforms with our common-sensical intuitions of future and past, where the future contains open possibilities and the past is fixed. This idea also allows us to give some physical account of the present moment, of 'now', the instant when the collapse occurs.

We think of physical states in the past as determining future events. But if physical law is time-invariant, wouldn't that suggest that it's equally true that the future determines the past? If we had a description of future physical states, we arguably could run the equations of physics backwards to determine the past states.

Cosmology reveals a dramatic difference between one temporal direction and the other, since one converges in the big bang and the other seemingly spreads out and dissipates. My own intuition tells me that there's something very important about that, but I still don't understand what it is. This evident dissimilarity between one temporal direction and the other creates an assymmetry all right, but it doesn't explain why the big bang lies in the pastward direction and not in the future. Why shouldn't we say that it's a big crunch that's still to come?

I guess that whether we call it past or future, one direction in time is known to us (however imperfectly) because of what we interpret as its traces: memories, fossils, archaeological evidence, cosmological observations and so on. We could reverse time and interpret them as precursers of future events, evidence of what the future holds that are absorbed and disappear when the events they presage occur, but regardless of which way the arrow of time points, time assymmetry certainly seems to exist. The two temporal directions certainly don't appear to us to be the same. Time is anisotropic.

Subjectively, for humans, perhaps the most important arrow is the psychological one. Memories either build up or dissappear over intervals, depending on what we imagine the direction of time is. Subjectively though, the feeling that the passage of time is directional, from the past towards the future, is almost overwhelming. It's difficult to even conceive of time unfolding in reverse. I'd speculate that there's something innate in us as biological organisms that makes us experience and conceptualize time in the ways that we do.

 

Thank you Yazata for the Philosophical interpretation.

 

It is when times arrow is determined by and will always be tethered to the past anyway and the past can be the future again.

 

That sounds like a great political platform, given the choices we currently have. The past never looked so cool, less populated and hospitable. Remember when you could count all the candidates for president on one hand and have fingers left?

 

This can still be worked out, but "Going back in time" no way...

2 X 0 + 2 X 0 = 10 X 0 + 7 1/2 X 0 = 0

So, dividing by zero*, you get

2 + 2 = 17 1/ 2.

* when in BH do what BH does

 

Energy in this universe comes in two modes of propagation: rotational and linear. For both modes of propagation, time as we understand it is suspended. If bound energy such as ourselves could achieve light speed, it would take no time whatsoever to cross the known universe or to travel in a straight line from minus infinity to plus infinity. For the rotational propagation mode of energy that is matter, it would likewise require nothing like the passage of time for it to propagate in all of an infinite number of directions at once, or in the case of Higgs (which has a spin of zero) to spin in diametrically opposite infinite number of directions at the same instant of time. But a mechanism must exist for time dilation to occur. What do you suppose that mechanism is?

But if you are a mathematician like Minkowski who it seems was a specialist in quadratics, what you do instead is to muck up our ideas about time by proposing a mangled quadratic Pythagorean-complex covariant relationship between time and space that never existed, and so then you require 4D spacetime after the ideas of his most brilliant and preferred student Hilbert in order to explain spacetime instead of the more elegant approach of EVERY dimension we see as light travel time, which is traceable to his mediocre student Einstein. Every dimension is time. Space between atoms or between nuclei and electron clouds contract like wavelengths that are simply Doppler shifted, because that is exactly what happens. Space is light travel time, and time proceeds at different rates for observers riding gigantic or microscopic versions of hour, minute, and second hands of a mechanical clock, depending on their respective distances from the center of rotation.

And people and especially mathematicians went for Minkowski's version of spacetime like it was a flat Earth or Ptolemy himself, or even a stacked herd of gigantic, equally ignorant turtles all the way down.

People are idiots. Infinitely so. The passage of time does not seem to have any effect whatsoever on intellectual inertia where ignorance is concerned. The more ignorant an idea, the more intellectual inertia it seems to have.

The ideas of someone like Donald Trump are one modern example everyone can agree on. Very ignorant. LOTS of intellectual inertia. Others?

 

According to Tegmark, there are only 32 number-sets (values) plus a handfull of *constants* or *common denominators*, equations based on the mathematical nature of physical principles. If time can be proven to be a mathematical function, I am not sure if you can rewind the movie, which itself continues to emerge as => as a result of change.

I see the *time* aspect as a mathematical problem. By traveling back in time you are *undoing* physical principles, including yourself. The moment You step physically back to a previous time, you will cease to exist in the present and lose the knowledge of the present, unless you use some kind of *loop* process, such as telescopes. You can see the past but have no influence over it in any way. You might be able to observe that present time, but be unable to participate unkess exactly as you were then, without memory of the future.

I believe Bohm's Fluid mechanics demostrates the *Implicate" is an unfolding proces which requires time, and trying to reverse the unfolding process, exactly follows mathematical functions both ways, but do not affect the chronological *addition of time* for any change.

I agree.

 

Hmmm.....mathematical time and physical time are bothe the same.

Both are based on the dynamics of all objects ; individually and within a system.

And these objects can only flow in a circular way ; not in arrow direction.

Recycle( circular); arrow(infinity, non-recycle)

 

What are the physical properties of time itself? Can you measure time with time?

I agree, but that does not prove time exists, other than as a measurement of duration of the physical dynamics.

Well, that is the question, isn't it?

Even though *individual* time-lines may seem circular (as a result of the circular motion of physical objects), the arrow of time of the *pilot wave* (the universal time-line) is always forward, regardless of circularity of dynamic change within.
example: It took the rider 2.75 minutes to complete the velodrome (time created from a circular measurement). During this measurement of time, the forward *arrow of time* of the Universe itself became 2.75 minutes longer.

IMO, Time itself is not a physical thing. It does not move in and of itself, it is a potential (latent ability) of the permittive condition which allows for change. And it is always additive or forward as part of the Pilot Wave.

From what I understand, the *Pilot wave* theory implies a wavefunction *expanding forward in all directions*, except back into the past.

 

Wow! I'm impressed with this thread (until it broke down!)

 

And this due to a lack of pertinent information or you inability to understand it?

 

IMO, yes. I find a greate difference in the assumption of eternal time in a timeless precondition of a *zero state* non-physical condition, and the concept of emerging time, which only becomes apparent during measurabe dynamic physical change.

Remeber time is inextricably connected with the existence of the physical universe, thus the term *spacetime* which are inseperable as independent phenomena.

 

I agree. Is this the same as zero state minus zero state giving us space-time? As you may have noticed when space or time has gone, it's gone. When dividing by zero there is nothing to divide: we have the same answer we began with; X. This is the same as any other operator: there is nothing to work with so it is essentially disregarded leaving the original answer.

Yeah going back in time? It's impossible to change the past

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Once it's gone it's gone. Anyways hope you enjoy your holidays. Merry Christmas and have a Happy New Year

 

Peace and Good Will to all.