6 ms·

The New Thermodynamic Understanding of Clocks

90 points by signa11 5y ago

efitz 5y ago
This article (and the underlying research) is very interesting. The article describes a clock as a “flow meter for entropy”. That is, that a clock is anything that measures the rate at which entropy is increasing in a system. The other major idea is that the more energy introduced into the clock, and the more entropy produced, the more accurate the clock.
motohagiography 5y ago
Total ignorant newb question, but the inconsistency the article talks about in measuring time in quantum systems, if that gap were related to the lack of gravitational effects at the quantum scale, and quantum weirdness is precisely about simultenaeity and problems with reconciling states with time measurements, is it because gravity and time are really just effectively the same thing? Logically, both time and gravity are essentially inferred substrates to how we observe space and mass/energy. Regarding the explanation in the article about how they're using thermodynamic entropy and information entropy together as a defining gauge for clocks at all scales, I would wonder if time relates to mass and gravity the way width relates to height, in that one is conceptually "perpendicular" to the other, and what it might mean for time to be perpendicular to gravity (if they weren't just the same thing). Last I read, there wasn't a full quantum theory of gravity that is consistent with experimental observations of macro gravity via relativity because of quantum "weirdness," because at that quantum scale there is almost no physical "time" effect other than entropy that we use as a reference. What we call quantum weirdness could literally just be the lack of time effects preventing things from happening all at once, and it's absent because gravity at that scale is effectively absent. No gravity, no time (quantum weirdness). Less gravity from being far from a well, faster time (aging effects). Total singluarity gravity, stretched time over its horizon (black hole time). When you never see them together, I'm just saying it starts to looks suspicious. I only mention it because I was literally just on a crazy bit that started with the joke where someone said, "faster than light travel is impossible," and ever the optimist I said, "helicopters, also impossible," which is funny to anyone who knows about helicopters. It turned into whether instead of super massive objects distorting space, there could be lower energy pulses and oscillations with effects like a resonant frequency, where instead of causing big distortions, could cause whorls and ripples of equivalent "space-turbulence" around them - not unlike the conceptual effect of helicopter blades, but using EM, and likely from an element or crystaline structure that facilitated an amplification feedback loop. You could detect the distortions because they would become "cold," as the space around them "spread." If gravity and time were the same thing, you could create a wave in space using turbulence and travel the substrate (time/gravity) directly. Faster than light travel is impossible only in space, where in a time/gravity substrate it's moot. Totally sci-fi speculation, but as a result I have since put a sticker on my eurorack synth that says, "danger: time machine" But seriously, how much confidence do we have that time and gravity are NOT the same thing?
- bryan0 5y ago
  > is it because gravity and time are really just effectively the same thing? Well gravity is the curvature of spacetime. So maybe not time exactly. It seemed like the question that needed to be answered was does the inherit randomness of a clock tell us anything about spacetime itself? Or is it just telling use how well we can measure it?
guerrilla 5y ago
I found this beautiful. This research is really probing something concrete which looks quite productive. I found the presentation to be excellent too. It took me a while to understand things well enough to be able to summarize things like that. Anyway, I love this particular direction since I've long been fascinated by the idea of change being more fundamental than time and thermodynamic theories of time. [1] 1. https://plato.stanford.edu/entries/time-thermo/ https://plato.stanford.edu/entries/time-thermo/
sixplusone 5y ago
Do you really need "infinite" energy? the universe is a giant clock, a perfect timekeeping device for itself; but then we have nothing to compare it to.
wayfarer1291 5y ago
The hypothesis considered at the very end of the article is intriguing. Time is generally viewed as a smooth variable. But fundamental thermodynamic limits on clocks suggest that there are in fact discrete steps occurring which we smooth over since they are below our measurement capabilities in general. I'm not entirely sure what the implications would be, but it does sort of make sense that this is in fact true.
- bryan0 5y ago
  Right. Is this just a limit on our ability to measure, or a deeper truth about the nature of time? If QM is a guide then it might be a deeper truth.
  - cinquemb 5y ago
    > or a deeper truth about the nature of time You may be interested in "Time Orientability" [0] [0] https://www.youtube.com/watch?v=Mk7vkhT0UCM https://www.youtube.com/watch?v=Mk7vkhT0UCM
- crocal 5y ago
  This is the precise point of the famous article by Leslie Lamport on time, clocks and the ordering of events in a distributed system. I was surprised that it was not mentioned in this article, as it formalizes the link between this fact and the relativity of time.
ffhhj 5y ago
Now, how a clock decoupled from the environment would behave, according to the quantum Zeno effect? https://en.wikipedia.org/wiki/Quantum_Zeno_effect https://en.wikipedia.org/wiki/Quantum_Zeno_effect
dredmorbius 5y ago
Most clocks that we can think of involve a clear entropic flow as part of the intrinsic mechanism: an unwinding spring, falling sand, a descending weight, a discharging battery. But the very first clocks don't rely on this at least not as a principle mechanism. Sundials, early astronomical observatories such as Stonehenge, or simply observing transits and occlusions, don't involve an entropic process. Rather, they track the regular and sustained rotational or orbital movement of the Earth, Moon, and planets. They track the passage of periods of time, but that tracking itself doesn't necessitate entropic flow. (The light that's necessary to observe the movements, of course, does. But that would be part of any time-based observation, and isn't fundamental to the regular movement itself being measured.)
- zadler 5y ago
  The light is fundamental... without particles bouncing between planetary bodies there would be nothing keeping them in sync. Thought experiment: imagine a box through which 0 information passes; no light, heat, radio waves nothing. There’s a clock in the box. Does the clocks progress reflect the progress of time outside the box? No, because time is based on causality and in space that’s propagated largely by massless particles.
  - dredmorbius 5y ago
    Light is not keeping the Earth and Moon "in sync". Gravitational force is.[1] That force propogates at the speed of light. It isn't light itself. Light does play a role in illuminating the system, rendering it observable. It's a signalling component. But again, that's exogenous to the system itself. (See discussion of Maxwell's Daemon and the resolution of that paradox for the role of light in that specific thermodynamic process.) But, and this is key: ANY clock needs some way of passing information on to the observer. From TFA, that might be light, or sound, or chemical potential (received as the smell of rotting garbage). But that is a common element, part of the signalling mechanism, but not of the timekeeping mechanism itself. For an astronomical clock, in most cases, the regular rotational or orbital motion is the timekeeping mechanism. The signalling mechanism is entirely separate. E.g., in the Earth-Moon system, timekeeping is noted by both the daily rotation of the Earth, and the monthly orbit of the Moon. The kinetic energy of both those regular motions is not driven in any sense, nor is it measuring a decay.[2] The signalling comes from an exogenous light source (the Sun) which illuminates both bodies. But the Sun isn't powering the timekeeping mechanism in question. And is equally significant in providing the light necessary for you to read a wristwatch or wall clock (of a non-illuminated variety). ________________________________ Notes: 1. I'm going to leave discussion of just what gravity is and/or how it's manifested out of this discussion. Veritassium tackled this recently though: https://youtube.com/watch?v=XRr1kaXKBsU https://youtube.com/watch?v=XRr1kaXKBsU 2. Yes, there's tidal friction. That's removing energy from the system, and is measurable with sufficiently precise clocks and over time. But that's also incidental and secondary to the motions in quesiton. We could use far more remote bodies (e.g., the Earth and another planet) in which mutual tidal forces are minimal, to eliminate this consideration. Or presume tidally-locked bodies in which orbital / rotational kinetic energy and angular momentum are constant.
IIAOPSW 5y ago
>One major aspect of the mystery of time is the fact that it doesn’t play the same role in quantum mechanics as other quantities, like position or momentum; physicists say there are no “time observables” There sort of is though. No fundamental force is time dependent per se. Here is a simple recipe: 1. Introduce a "clock system" to your experiment, whose job it is to be in state |t> at time t. Notice that the eigenstates of the clock system are the same as the quantum fourier transform. The clock Hamiltonian is thus easy to construct. 2. Change any time dependent term in the Hamiltonian into an interaction term between the original system and the clock system. In other words, rewrite H(t)|x> as H|t>|x>. 3. Solve as a time independent Hamiltonian. 4. Time is now an observable |t>. Oddly, it is now entangled with position states |x>. To make an analogy, instead of having a time dependent force you can imagine your experiment is being conducted on a train moving at constant speed, and the time dependent part is encoded in the curves of the track. Technically the particles of the experiment apply a reaction force on the clock system, but assuming your commuter train is several tons heavier than your subatomic particles this is irrelevant (except of course to get theoretical perfection one requires infinite mass). The entanglement aspect is just another way of saying that if you observe the 3:15 to Yuma at the station, this is highly correlated with observing the time 3:15 on the clock system. The rest of the article is interesting.
- ithkuil 5y ago
  If speed (momentum) is an observable then either time is also an observable or are we saying that speed is more fundamental?
- abdullahkhalids 5y ago
  If there is a time-observable, what is the conjugate observable (which must exist by definition of operators on Hilbert space)? And how do you measure this conjugate observable?
  - IIAOPSW 5y ago
    Energy. Indeed the time/energy uncertainty relation is already well known.
hasmanean 5y ago
I think they are missing one concept in their analysis. A clock by definition is something that produces a regular series of pulses. In other words its signal is sparse in the frequency domain. To keep it sparse, you constrain it by its geometry (if it’s electrically driven then you contain the fields in a narrow region of space). If it’s mechanical you constrain its physical dimensions etc. And finally you filter out thermal noise by lowering the entropy of the system. This is where standard thermodynamics enters into the picture…to cool the clock (say) you have to increase the entropy of the universe. The “lab conditions” under which you operate the clock though, are a low entropy zone. But the nature of pure oscillations has no dependence on entropy—quite the reverse, the clock itself operates in a low entropy environment. In other words you can predict exactly what frequency state it’s in. Proof of this is the fact that you can print the frequency on the outside of the box in permanent paint. Astronomical bodies float in space and they are already in a sparse environment as far as gravity is concerned. There are 7 major planets besides earth and the sun has most of the mass of the solar system. The spaces between the planets are relatively debris free. The asteroid belt is quasi-uniform. So they move kind of regularly. Where they couple energy between planets that can be predicted using Newtons laws. What makes it a clock is the empty space between the planets. If the solar system was full of dust with storms etc then the motion of the planets would be subject to “weather” like conditions and nobody would treat it like a clock (just as we don’t keep time by the arrival of the rain). We’re spoiled on earth by the presence of this regular motion on the skies above that is independent of all that is happening in earth. So that’s where our notion of a “fixed” absolute clock comes from. What does this mean for atomic clocks? In the lab we try to reproduce these space like conditions (by keeping air currents, external stimuli out) and think that vibrating atoms are telling us something absolute about nature. It’s perhaps better to say that they are relatively more stable than our living environments and independent of whatever we are trying to measure. But is there some master clock in the universe that these atoms are tapping into and recording for us? No. There’s no such thing. They are just drums that beat to their own tune which happens to be defined by their dimensions and the local properties of space around them. The fact that all atoms of the same type under the same conditions are all the same size makes atomic clocks possible.

90 points by signa11 5y ago

This article (and the underlying research) is very interesting. The article describes a clock as a “flow meter for entropy”. That is, that a clock is anything that measures the rate at which entropy is increasing in a system. The other major idea is that the more energy introduced into the clock, and the more entropy produced, the more accurate the clock.

motohagiography 5y ago

Total ignorant newb question, but the inconsistency the article talks about in measuring time in quantum systems, if that gap were related to the lack of gravitational effects at the quantum scale, and quantum weirdness is precisely about simultenaeity and problems with reconciling states with time measurements, is it because gravity and time are really just effectively the same thing? Logically, both time and gravity are essentially inferred substrates to how we observe space and mass/energy. Regarding the explanation in the article about how they're using thermodynamic entropy and information entropy together as a defining gauge for clocks at all scales, I would wonder if time relates to mass and gravity the way width relates to height, in that one is conceptually "perpendicular" to the other, and what it might mean for time to be perpendicular to gravity (if they weren't just the same thing). Last I read, there wasn't a full quantum theory of gravity that is consistent with experimental observations of macro gravity via relativity because of quantum "weirdness," because at that quantum scale there is almost no physical "time" effect other than entropy that we use as a reference. What we call quantum weirdness could literally just be the lack of time effects preventing things from happening all at once, and it's absent because gravity at that scale is effectively absent. No gravity, no time (quantum weirdness). Less gravity from being far from a well, faster time (aging effects). Total singluarity gravity, stretched time over its horizon (black hole time). When you never see them together, I'm just saying it starts to looks suspicious. I only mention it because I was literally just on a crazy bit that started with the joke where someone said, "faster than light travel is impossible," and ever the optimist I said, "helicopters, also impossible," which is funny to anyone who knows about helicopters. It turned into whether instead of super massive objects distorting space, there could be lower energy pulses and oscillations with effects like a resonant frequency, where instead of causing big distortions, could cause whorls and ripples of equivalent "space-turbulence" around them - not unlike the conceptual effect of helicopter blades, but using EM, and likely from an element or crystaline structure that facilitated an amplification feedback loop. You could detect the distortions because they would become "cold," as the space around them "spread." If gravity and time were the same thing, you could create a wave in space using turbulence and travel the substrate (time/gravity) directly. Faster than light travel is impossible only in space, where in a time/gravity substrate it's moot. Totally sci-fi speculation, but as a result I have since put a sticker on my eurorack synth that says, "danger: time machine" But seriously, how much confidence do we have that time and gravity are NOT the same thing?

bryan0 5y ago
> is it because gravity and time are really just effectively the same thing? Well gravity is the curvature of spacetime. So maybe not time exactly. It seemed like the question that needed to be answered was does the inherit randomness of a clock tell us anything about spacetime itself? Or is it just telling use how well we can measure it?

guerrilla 5y ago

I found this beautiful. This research is really probing something concrete which looks quite productive. I found the presentation to be excellent too. It took me a while to understand things well enough to be able to summarize things like that. Anyway, I love this particular direction since I've long been fascinated by the idea of change being more fundamental than time and thermodynamic theories of time. [1] 1. https://plato.stanford.edu/entries/time-thermo/ https://plato.stanford.edu/entries/time-thermo/

sixplusone 5y ago

Do you really need "infinite" energy? the universe is a giant clock, a perfect timekeeping device for itself; but then we have nothing to compare it to.

wayfarer1291 5y ago

The hypothesis considered at the very end of the article is intriguing. Time is generally viewed as a smooth variable. But fundamental thermodynamic limits on clocks suggest that there are in fact discrete steps occurring which we smooth over since they are below our measurement capabilities in general. I'm not entirely sure what the implications would be, but it does sort of make sense that this is in fact true.

bryan0 5y ago
Right. Is this just a limit on our ability to measure, or a deeper truth about the nature of time? If QM is a guide then it might be a deeper truth.
- cinquemb 5y ago
  > or a deeper truth about the nature of time You may be interested in "Time Orientability" [0] [0] https://www.youtube.com/watch?v=Mk7vkhT0UCM https://www.youtube.com/watch?v=Mk7vkhT0UCM
crocal 5y ago
This is the precise point of the famous article by Leslie Lamport on time, clocks and the ordering of events in a distributed system. I was surprised that it was not mentioned in this article, as it formalizes the link between this fact and the relativity of time.

ffhhj 5y ago

Now, how a clock decoupled from the environment would behave, according to the quantum Zeno effect? https://en.wikipedia.org/wiki/Quantum_Zeno_effect https://en.wikipedia.org/wiki/Quantum_Zeno_effect

dredmorbius 5y ago

Most clocks that we can think of involve a clear entropic flow as part of the intrinsic mechanism: an unwinding spring, falling sand, a descending weight, a discharging battery. But the very first clocks don't rely on this at least not as a principle mechanism. Sundials, early astronomical observatories such as Stonehenge, or simply observing transits and occlusions, don't involve an entropic process. Rather, they track the regular and sustained rotational or orbital movement of the Earth, Moon, and planets. They track the passage of periods of time, but that tracking itself doesn't necessitate entropic flow. (The light that's necessary to observe the movements, of course, does. But that would be part of any time-based observation, and isn't fundamental to the regular movement itself being measured.)

zadler 5y ago
The light is fundamental... without particles bouncing between planetary bodies there would be nothing keeping them in sync. Thought experiment: imagine a box through which 0 information passes; no light, heat, radio waves nothing. There’s a clock in the box. Does the clocks progress reflect the progress of time outside the box? No, because time is based on causality and in space that’s propagated largely by massless particles.
- dredmorbius 5y ago
  Light is not keeping the Earth and Moon "in sync". Gravitational force is.[1] That force propogates at the speed of light. It isn't light itself. Light does play a role in illuminating the system, rendering it observable. It's a signalling component. But again, that's exogenous to the system itself. (See discussion of Maxwell's Daemon and the resolution of that paradox for the role of light in that specific thermodynamic process.) But, and this is key: ANY clock needs some way of passing information on to the observer. From TFA, that might be light, or sound, or chemical potential (received as the smell of rotting garbage). But that is a common element, part of the signalling mechanism, but not of the timekeeping mechanism itself. For an astronomical clock, in most cases, the regular rotational or orbital motion is the timekeeping mechanism. The signalling mechanism is entirely separate. E.g., in the Earth-Moon system, timekeeping is noted by both the daily rotation of the Earth, and the monthly orbit of the Moon. The kinetic energy of both those regular motions is not driven in any sense, nor is it measuring a decay.[2] The signalling comes from an exogenous light source (the Sun) which illuminates both bodies. But the Sun isn't powering the timekeeping mechanism in question. And is equally significant in providing the light necessary for you to read a wristwatch or wall clock (of a non-illuminated variety). ________________________________ Notes: 1. I'm going to leave discussion of just what gravity is and/or how it's manifested out of this discussion. Veritassium tackled this recently though: https://youtube.com/watch?v=XRr1kaXKBsU https://youtube.com/watch?v=XRr1kaXKBsU 2. Yes, there's tidal friction. That's removing energy from the system, and is measurable with sufficiently precise clocks and over time. But that's also incidental and secondary to the motions in quesiton. We could use far more remote bodies (e.g., the Earth and another planet) in which mutual tidal forces are minimal, to eliminate this consideration. Or presume tidally-locked bodies in which orbital / rotational kinetic energy and angular momentum are constant.

IIAOPSW 5y ago

>One major aspect of the mystery of time is the fact that it doesn’t play the same role in quantum mechanics as other quantities, like position or momentum; physicists say there are no “time observables” There sort of is though. No fundamental force is time dependent per se. Here is a simple recipe: 1. Introduce a "clock system" to your experiment, whose job it is to be in state |t> at time t. Notice that the eigenstates of the clock system are the same as the quantum fourier transform. The clock Hamiltonian is thus easy to construct. 2. Change any time dependent term in the Hamiltonian into an interaction term between the original system and the clock system. In other words, rewrite H(t)|x> as H|t>|x>. 3. Solve as a time independent Hamiltonian. 4. Time is now an observable |t>. Oddly, it is now entangled with position states |x>. To make an analogy, instead of having a time dependent force you can imagine your experiment is being conducted on a train moving at constant speed, and the time dependent part is encoded in the curves of the track. Technically the particles of the experiment apply a reaction force on the clock system, but assuming your commuter train is several tons heavier than your subatomic particles this is irrelevant (except of course to get theoretical perfection one requires infinite mass). The entanglement aspect is just another way of saying that if you observe the 3:15 to Yuma at the station, this is highly correlated with observing the time 3:15 on the clock system. The rest of the article is interesting.

ithkuil 5y ago
If speed (momentum) is an observable then either time is also an observable or are we saying that speed is more fundamental?
abdullahkhalids 5y ago
If there is a time-observable, what is the conjugate observable (which must exist by definition of operators on Hilbert space)? And how do you measure this conjugate observable?
- IIAOPSW 5y ago
  Energy. Indeed the time/energy uncertainty relation is already well known.

hasmanean 5y ago

I think they are missing one concept in their analysis. A clock by definition is something that produces a regular series of pulses. In other words its signal is sparse in the frequency domain. To keep it sparse, you constrain it by its geometry (if it’s electrically driven then you contain the fields in a narrow region of space). If it’s mechanical you constrain its physical dimensions etc. And finally you filter out thermal noise by lowering the entropy of the system. This is where standard thermodynamics enters into the picture…to cool the clock (say) you have to increase the entropy of the universe. The “lab conditions” under which you operate the clock though, are a low entropy zone. But the nature of pure oscillations has no dependence on entropy—quite the reverse, the clock itself operates in a low entropy environment. In other words you can predict exactly what frequency state it’s in. Proof of this is the fact that you can print the frequency on the outside of the box in permanent paint. Astronomical bodies float in space and they are already in a sparse environment as far as gravity is concerned. There are 7 major planets besides earth and the sun has most of the mass of the solar system. The spaces between the planets are relatively debris free. The asteroid belt is quasi-uniform. So they move kind of regularly. Where they couple energy between planets that can be predicted using Newtons laws. What makes it a clock is the empty space between the planets. If the solar system was full of dust with storms etc then the motion of the planets would be subject to “weather” like conditions and nobody would treat it like a clock (just as we don’t keep time by the arrival of the rain). We’re spoiled on earth by the presence of this regular motion on the skies above that is independent of all that is happening in earth. So that’s where our notion of a “fixed” absolute clock comes from. What does this mean for atomic clocks? In the lab we try to reproduce these space like conditions (by keeping air currents, external stimuli out) and think that vibrating atoms are telling us something absolute about nature. It’s perhaps better to say that they are relatively more stable than our living environments and independent of whatever we are trying to measure. But is there some master clock in the universe that these atoms are tapping into and recording for us? No. There’s no such thing. They are just drums that beat to their own tune which happens to be defined by their dimensions and the local properties of space around them. The fact that all atoms of the same type under the same conditions are all the same size makes atomic clocks possible.