# Running in Ticks

1. Dec 3, 2014

### Filip

I have been wondering this for a uncomfortable amount of time...
Does the universe have a defined tick rate?
By tick rate I mean a loop that processes all information and changes in the universe in that moment, similar how a video game or a computer processor work.
I was also wondering if that tick rate is the planck time.

2. Dec 3, 2014

### ShayanJ

In classical physics, it was assumed that there is such a universal tick. But in SR, this assumption is relaxed. So I think your answer is no!
And Plank time is only a number with the unit of time. Nothing more, nothing less!

3. Dec 3, 2014

Interesting.

4. Dec 4, 2014

### marcus

Filip, your post opens the door to several interesting questions. I hope you keep probing in that direction.
I agree with Shyan saying in effect "no. we don't know of any universal clock frequency"
but wondering about time does not necessarily stop there.

Wondering does not stop for me, at that point, and maybe also does not stop for you.

You know about gravitational time dilation. Natural processes including clocks, and chemistry in our bodies, go slower with depth in a gravity well. It has been shown experimentally that atomic clocks (counting cycles of a resonant frequency of the Cesium atom) go faster in the upper floors of a building than they do in the lower floors. the passage of time depends on altitude. Clocks in satellites up in orbit go faster because they are higher (effect partly but not entirely cancelled by their speed relative to ground).
The universe is running on many different "times".

It seems, on that account alone, impossible for there to be a "master clock" or "master frequency" for the universe. The same natural process proceeds at different rates all over the place.

Peter Lorre has a thoughtful meditation about time which he delivers in the Bogart&Lollobrigida movie "Beat the Devil". It would be on Youtube.

Seriously, for me physical quantities have to be defined OPERATIONALLY. At any stage in the evolution of the universe, for time to have physical meaning it would have to be possible, at least in principle, to MEASURE it.

that means there has to be some repetitive CYCLE (like a pendulum, or a quartz crystal vibration, or atomic resonance microwave hum) whose cycles can be COUNTED. If not, then time (operationally speaking) does not exist.

If you want, think about what the minimum amount of complexity a universe would need to have to support approximately regular repetitive cycles and a counter. Counting is not altogether trivial. In volume 1 of the Feynman lectures there is a discussion of "ratchet and pawl" that touches on the requirements for a counter to work and not accidentally run backwards now and then. But for starters, I would just think about what it takes to support cyclical processes, and not worry about counting.

There was recently a research paper you can get simply by googling "silent initial conditions" (without the quotes) which suggests that right around the start of expansion (aka "big bang") time would not have existed because physical nature was too simple for an oscillator or any cyclical process to be constructed!
If you google "silent initial conditions " and find it (at the arXiv.org site) you will see it is by Mielczarek, Linsefors, Barrau (polish, swedish, french physicists). I like the paper but of course it is too early to believe what they are proposing. Just something to know about.

Last edited: Dec 4, 2014
5. Dec 4, 2014

### Filip

Thanks so much for your post, I cannot comprehend how as you said, time could be measured if there is no time it takes to increment that time, you would think that everything would have happened in the universe already from the start of the big bang if there wasn't some sort of thing preventing all of time to be traveled all at once.

A question I have relating to this is how motion works. I understand most of the basics such as how giving something kinetic energy makes it move, inertia, momentum and such, but I do not understand what dictates how this object moves through space, and at which precise moment it starts moving given this kinetic energy.

6. Dec 4, 2014

### marcus

Here is the clip from Beat the Devil where Peter Lorre discourses about time

7. Dec 4, 2014

### marcus

You are trying to think about physics at a very basic level. I try also, sometimes. Currently I am fascinated by the idea that the universe has a FROZEN PHASE at extremely high density near start of expansion, a so-called "Euclidean" phase in which nothing can move, neighboring points cannot interact. It is the "silent initial condition" that paper talks about. They offer some mathematics about the "melting" of that phase and the opening out of lightcones which permits causality to begin widening out.
If you google "silent initial conditions" i think you will get this:
Silent initial conditions for cosmological perturbations with a change of space-time signature
Jakub Mielczarek, Linda Linsefors, Aurelien Barrau
(Submitted on 2 Nov 2014)
Recent calculations in loop quantum cosmology suggest that a transition from a Lorentzian to an Euclidean space-time might take place in the very early Universe. The transition point leads to a state of silence, characterized by a vanishing speed of light. This behavior can be interpreted as a decoupling of different space points, similar to the one characterizing the BKL phase.
In this study, we address the issue of imposing initial conditions for the cosmological perturbations at the transition point between the Lorentzian and Euclidean phases. Motivated by the decoupling of space points, initial conditions characterized by a lack of correlations are investigated. We show that the "white noise" initial conditions are supported by the analysis of the vacuum state in the Euclidean regime adjacent to the state of silence.
Furthermore, the possibility of imposing the silent initial conditions at the trans-Planckian surface, characterized by a vanishing speed for the propagation of modes with wavelengths of the order of the Planck length, is studied. Such initial conditions might result from a loop-deformations of the Poincaré algebra. The conversion of the silent initial power spectrum to a scale-invariant one is also examined.
12 pages, 8 figures

My advice would be: don't be put off by the technical language. just click on PDF (over on the upper right of the summary page) and scroll down to the figure 5 on page 8
that shows the lightcones shrunk to vertical lines (basically a 4d picture of a static 3d world).
and then opening out to normal 45 degree cones

Last edited: Dec 4, 2014
8. Dec 4, 2014

### Filip

The technical language is the thing that hinders me most in reading scientific papers like this. It really distracts me from understanding what the paper says.

For example, what is a trans-Planckian surface? What is "vanishing speed for the propagation of modes"?
What do you mean by modes?

9. Dec 4, 2014

### marcus

Words can get in the way. when you google "s.i.c." you get http://arxiv.org/abs/1411.0272
and when you get the summary page and click on pdf
you get the whole article (12 pages I think)
and you scroll down to page 8 and look at figure 5
you see a diagram of what I would call the "melting" of the static "Euclidean phase" as interaction starts up, and motion becomes possible

Don't worry about understanding all the verbiage, thats how they communicate (birds communicate, different species of professionals communicate)
Get the gist.

10. Dec 4, 2014

### marcus

I think modes means modes of vibration or waving and in quantum field theory, where particles are "twangs" of the underlying field, propagation of modes could mean propagation of particles. "speed of propagation of modes" is probably just a way of being more inclusive and saying "speeds of propagation of light and other particle-wave stuff"

"Transplankian surface" would just be the place where, as you work your way back in time, using the expanding universe model that they use, the ENERGY DENSITY gets above some critical value, like the planck unit of energy density. Or half the planck energy density. Something like that.

That energy density is amazingly high. Energy density (or mass density) is usually denoted with lowercase Greek letter rho. ρ
It looks like our letter p, often confused. You probably know all this. So in the paper they have something they call ρplanck
it is an unimaginably high energy density. that is where (according to the Lqg analysis) quantum effects kick in and a collapsing universe bounces and starts to re-expand.

So maybe "transplanckian" means ρ > ρplanck/2

the estimate of at what density it happens is a detail: not so important and bound to be preliminary. What I found exciting about the article was the idea that high density could freeze out interaction and the image of the lightcones shrinking closed and then opening up again after the bounce.

after a frozen, essentially timeless, phase. Earlier Lqg computer simulations of the cosmological bounce have not included this feature. they have run using a simpler model in which this phase change did not occur. Same with analytical solutions using equation models. So the Mielczarek Linsefors Barrau idea is NEW (or so it seems to me, as non-expert spectator). It may be wrong, it may get shot down, but right now it definitely seems worth knowing of and thinking about.

Last edited: Dec 5, 2014
11. Dec 4, 2014

### marcus

Another funny thing about it is that it recovers a famous conjecture arrived at by CLASSICAL Gen Rel analysis by famous Russian physicists whose initials were B, K, and L.
They were trying to explore what the "singularity" would actually look like and found a kind of chaotic behavior over a 3d surface bounding the 4d region where the GR equation worked and this chaotic behavior amounted to a breakdown of communication between neighbor points. So that was called "BKL conjecture".
It sometimes a good sign when modern quantum analysis gives results which resemble venerable classical results. BKL's conjecture was some 45 years back. They had belonged to Lev Landau's research group.

Last edited: Dec 4, 2014
12. Dec 5, 2014

### Lord Crc

Being a programmer with an interest in physics my way of thinking about this is to imagine a simple electronic circuit which has a clock pulse as input. In order for the circuit to be "aware" there even is time, some memory is needed to store the previous input or output for example.

However, given that the clock pulse is the only input it cannot tell the rate at which the input clock pulse cycles, it can just detect that it changes. So as far as this circuit is concerned, the clock rate not physical.

Anyway, perhaps you might find the following talk by Lee Smolin interesting. It's a rather unorthodox idea he's presenting, so keep that in mind. It's very accessible though.

The universe as a process of unique events.
http://pirsa.org/13020146/

13. Dec 5, 2014

### jerromyjon

I was thinking yesterday about a clock which "ticks" according to the speed of light, which would of course be a constant in any reference frame. The problem remains in that any other observer would still see time dilated pulse rates, meaning time is relative. Since it has to be relative, a "smallest" tick in one frame might not be the same in another reference frame.

On the other hand there may be some "quickest" interaction which could be viewed as a minimum quanta of time but it would only make sense if every physical action evolved in denominations of this quanta.

14. Dec 5, 2014

### marcus

Jerromy, I think to make a clock that uses the speed of light you also need a fixed LENGTH, like the distance between two mirrors. Speed by itself is not enough there must be another quantity in order for a cycle to emerge and time to be counted. The fixed length would not be the same to all observers. So the clock rate would not seem the same to all. Just my take on it.

Crc, that talk by Smolin was indeed interesting. I remember watching the pirsa video around Feb 2013. Smolin's book with Unger has come out in e-book (Kindle). The paper edition had not come out last time I checked but is expected soon. The title is The Singular Universe...

The book will have a lot about the evolution of laws of physics and "therefore" (reasoning from the idea that laws must have evolved) the fundamental reality of time. It will CONTINUE what you saw in the 2013 pirsa talk.

But also a more concentrated continuation is to be seen in the CORTES AND SMOLIN paper you get by googling [cortes causal spinfoam] as in my signature. Paste it in without the square brackets.

Or to be more certain of getting to the free online arXiv copy of the paper, google
[cortes arxiv causal spinfoam]

This was July 2014, the latest in the series. I think it is possible for laws to evolve atemporally so that you can have laws explained by an evolutionary process WITHOUT positing the fundamental reality of time. I find what Cortes and Smolin are doing extremely interesting (Unger's part in it less so). But I do not find it entirely convincing. I'm very glad you mentioned his February 2013 PIRSA talk.

Last edited: Dec 5, 2014