The crisis inside the physics of time | Hacker News Reader

The crisis inside the physics of time

nautil.us

49 pointsdnetesn50 comments

> We don’t see, hear, smell, touch, or taste time. And yet we somehow measure it.

I’m not sure we measure time. What we measure is distance. What is called a clock is always an oscillator. This oscillator is used as unit distance. Then this unit distance is counted. The distances are converted with appropriate choice of units for counting. I don’t see how comparing two distances can be called “meausuring time”. Maybe I’m missing something here, I don’t know. For instance, we measure the period of a pendulum. This is distance not time. Can anyone clarify how “time” enter in mesurement of distances? Thanks.

To be fair, you keep using words like “measure” and “compare” which implies an interval or something more than space right there. Without time how can you take a measurement or make a comparison? If I throw a ball to you and we both nite a change in distance occurring, over what is that change occurring? It’s baked right into something as basic as the formula for velocity = d/t. Time is difficult to define without reference to space, and measurements of the evolution of a system, which may be the problem I guess? What would time be in a purely static, closed system? What would time be after the complete heat death of the universe?

The article seems to suggest But as the balloon blows up, the curvature of its surface grows shallower and shallower. “The changing geometry,” explains Kucha, “allows you to see that you are at one instant of time rather than another.” In other words, it can function as a clock. Then goes on to point out that any given clock has limitations when applied to different regimes.

I’m a little concerned though, because the author seems to be under the somewhat common misapprehension that the Planck scale is some kind of limit on quantization, so the whole article might be... well... not fantastic. It is theorized thst below that you might get a spacetime foam, but the truth is that may or may not be the case, and spacetime may not even be quantized. As in the case of so much regarding the base nature of spacetime, and the union of QM and GTR, we just don’t know.

> velocity = d/t.

Thanks for the example. Here d/t is a proportionality. Or at least half of a proportionality. But the terms of a proportianality must be of the same type. And here they both must be distance. Because we compare what is measured (distance d) to the unit distance, here denoted with the letter t.

I'm not denying the existence of time. I'm saying that we are not measuring time but comparing two distances.

You are saying that if time did not exist the oscillator would not oscillate. Maybe. But we are not measuring time but comparing two distances. We are counting how many unit distance there are in the distance to be measured.

> Time is difficult to define without reference to space, and measurements of the evolution of a system, which may be the problem I guess?

Same with the concept of space. What you call "space" is the distance between two points.

> What would time be in a purely static, closed system?

The system maybe static but this does not mean time is not passing. Time is still passing but there is no oscillator. Without an oscillator to define the unit distance you cannot count the distance to be measured.

> What would time be after the complete heat death of the universe?

This is the philosophic time and it is independent of our ability to measure it. So I'm not talking about the existence of time but about the measurement of time. Because I observe that what we do is compare two distances. I don't understand how comparing two distances is interpreted as "measuring time."

I also observe that no one else have any doubts that what is measured is time. So the problem must with me:)

> But the terms of a proportianality must be of the same type.

This is flat wrong. Pressure is measured in pounds per square inch. Are you suggesting weight and area are the same thing?

Reading the parent's comment history, I would characterize them as a physics crank.

First i thought to "say something about 'energy, maybe osscilating -and as well, there are some 'conditions' of energy', '...a perspective, to see energy as a wave with a known length , which shortend 'by time'" -but now i feel to tell you 'to see science as the mustard to a sausage in terms of change' ^^

It's certainly easier to be patronizing when you are being obscure, but if you suggest that my perspective is flawed without explanation, I really have no alternative but to dismiss that opinion.

Tryed to answer your patronizing problem:

> hint://deviantart.com/conversation-culture/gallery/

the comic-strips are 'named' 1...2...3 - hope that will help

Maybe... i am drunken enough ('Frühschoppen') to expand my forgone lines with: "To see energy as a wave with a fixed start- and endpoint, 'shorten by time'" (-:

Edited: i thought my original posting was 'too offensive, and rejecting' in terms of HN-Guidelines.

I’m not the parent commenter, but I think I can help clear up this confusion. Seems like you may have missed: > Or at least half a proportionality. I think their idea is that in the proportion A = B, where A = w/x and B = y/z, A and B must be “of the same type.” Applied to your example, I think PC might say that in a proportionality of pressures, A and B must be of the same type—-it is not the case that w and x must be of the same type.

> the author seems to be under the somewhat common misapprehension that the Planck scale is some kind of limit on quantization

The Planck length may not limit quantization, but it is a hard limit on measurement. Due to Heisenberg uncertainty, a photon that with a position small enough to do the measurement has a momentum so large the photon would collapse into a black hole (which would immediately evaporate).

I don't think this is right. Measuring a photons position to the plank length or below (probably not possible) would just mean the photon has a very large uncertainty in momentum.

But that's no different than saying if you take a single slice of a 44.1khz PWM data stream you'd have 100% certainty of amplitude and 100% uncertainty of frequency.

We don't hear, smell or taste light either but somehow measure it.

Exclusively using our unique human senses to reason about the nature of something seems pretty fallible.

OP didn't say anything about human senses. I don't see how your reply fits in, I think you may have misread the comment.

> > We don’t see, hear, smell, touch, or taste time. And yet we somehow measure it.

That's not from OP. He quoted it from somebody else!

Hm Well think about it...for just a moment...if there is something like a "sphere" for senses, one for the chemistry and one for the physics...the funny part maybe 3x(A= >0) ...and yes, there was a comic about ^^

Atomic clocks measure atomic state transitions. There is no distance here - the oscillations are in energy states, not position.

In fact, the atoms undergoing these state transitions are cooled as much as possible to prevent any sort of movement:

> The accuracy of an atomic clock depends on two factors. The first factor is temperature of the sample atoms—colder atoms move much more slowly, allowing longer probe times.

https://en.wikipedia.org/wiki/Atomic_clock

I sincerely apologize if I offended anyone's belief in physics. But at least I know that some of the greatest philosophers thought about the nature of Time the way I do. They said Time is not an independent physical entity to be measured. If you call me a crank, as @canhascodez did, for repeating what Aristotle, Leibniz, Kant, Bergson, Henry James and others said then so be it.

To clarify some more why I think time is not measurable I wrote a short essay and I posted here for anyone interested: https://docs.google.com/document/d/1cKtorWUj5lUeRXJ0iPB9kaLd...

I find that the quantum-information-theoretical interpretation of QM provides a very satisfying (to me) account of what time is. It's not a fundamental physical phenomenon, it's an emergent property (or perhaps it might be better called a side-effect) of decoherence, which leads to the emergence of classical reality from the quantum wave function:

http://blog.rongarret.info/2014/10/parallel-universes-and-ar...

If time is an emergent property shouldn't space be as well?

Yes.

https://en.wikipedia.org/wiki/Loop_quantum_gravity

What is an "emergent property"?

A particle can have intrinsic properties like charge and spin that are directly measurable attributes of the particle itself. Other properties like temperature and even size are called emergent because they’re not truly fundamental but rather “emerge” when we observe the particle in some system of other particles. We can measure emergent properties but they’re more akin to properties of the system as a whole than some specific attribute of one or more particle. I hope I made sense, it can be confusing.

Thanks for the simple answer. Wouldn’t temperature still be intrinsic? Assuming there’s only one particle in the universe it would still have a temperature right? Yes it’s not in relation to anything but then neither would charge be in our one particle example. I am the merest amateur so bear with me.

When you say "the gas in this container is 100'C," that is a statement about the vibration and motion of the molecules which constitute that gas. To say something is hot or cold is to say that the average molecule in that substance has or lacks kinetic energy. Therefore, temperature is a description of the kinetic motion in a system, and so it emerges from position and velocity.

Source: also an amateur

No, it would only have a state. In classical physics the state would be its Kinetic energy. In QE it would be.... well it’s state.

T is only defined in an ensemble of other particles, i.e. when you can no longer keep track the particles and it’s necessary to use averages. Then the T is the average kinetic energy.

Furthermore T is only technically defined in thermodynamic equilibrium, so nothing happens at all (otherwise you’re not in equilibrium).

Finally, you can have “negative temperature” I.e T < absolute zero, if you have population inversion (I.e. a lasing cavity) which is really an abuse of nomenclature since population inversion cannot occur in equilibrium (and therefore T is not defined). However, the Boltzmann (?) equations have pop inv. only when the the T parameter is negative (even though pop inv. is the “hotter” than infinitely hot).

All this to say that 1. T is not defined for a single particle 2. T is not well defined for very many systems at all!

Assuming there’s only one particle in the universe it would still have a temperature right?

Not really.

One (not quite universal) way to think of temperature is as a measure of average energy per degree of freedom (linear motion, rotational motion, vibration, ...). This assumes a system where random interactions spread the energy throughout, exciting all these different energy states. In contrast, when you take your single particle and add some energy, there's no spreading of anything and no excitation of other degrees of freedom - the system doesn't 'thermalize', and no average emerges.

Note that there are other ways to think about this, eg in terms of inverse temperature (thermodynamic beta), which is essentially a measure of phase space growth under addition of energy. Your single particle system will only exist in a single state no matter how much energy you add, so it's not really useful to take a thermodynamic approach...

An easier example to think about might be pressure. A single molecule free in a vacuum can’t be said to have a pressure, but put it in a container along with a few other molecules and it starts to become a useful property to measure and think about.

> More promising as a quantum clock is the geometry of space itself: monitoring spacetime’s changing curvature as the infant universe expands or a black hole forms. Kucha surmises that such a property might still be measurable in the extreme conditions of quantum gravity. The expanding cosmos offers the simplest example of this scheme. Imagine the tiny infant universe as an inflating balloon. Initially, its surface bends sharply around. But as the balloon blows up, the curvature of its surface grows shallower and shallower. “The changing geometry,” explains Kucha, “allows you to see that you are at one instant of time rather than another.” In other words, it can function as a clock.

Brilliantly said, wow!

> This is a picture so different from the world of classical physics that even Einstein railed against its indeterminacy. He declared that he could never believe that God would play dice with the world.

This is a common misconception.

Einstein kept pointing out that Quantum non-locality and the Relativistic limit of velocity at c are incompatible. Bohr ignored or misunderstood him and led everyone on a merry jaunt into irrelevancies. Now that non-locality is established we will hopefully see some new physics in this century.

Non-locality has nothing to do with randomness. How does the quote apply to that argument?

Isn't information theory a new way of thinking about time? Time, as change, is entropy, which, under certain formulations, is equal to uncomputability. In this way we could think of the flow of time as the march of some arbitrary computation which cannot be computed in advance, that is, ignoring time.

What formulations equate entropy with uncomputability? That doesn't seem to make much sense to me. Do you have a reference that I could read?

It is somewhat of a leap. However there are sensible formulations where it is pointed out that entropy is information, and "amount of uncomputability" is information in the sense that to know the output of an arbitrary Turing machine (which outputs either 0 or 1) one needs exactly one bit of information.

"the subatomic rules of quantum mechanics, which continue to work within a universal, Newtonian time frame"

Wait, what? QM is based on special relativity. It's problem with general relativity compatibility only remotely touches time, if at all.

Quantum mechanics is not based on special relativity at all. In fact, you can show that you can write Hamilton-Jacobi's equation (purely Classical Mechanics) as a limiting case of Schrodinger's equation.

It is true that QM came about initially as a problem with the quantization of the electromagnetic field, but that was a bit of an accident.

In vanilla QM, time is Newtonian - taken as a given, independent variable. You can "tack on time dependence" as it were. (Special) relativistic QM becomes quantum field theory (well, first Schrodinger's eq becomes the Klein Gordon equation, then Dirac stares into the fire and anti matter pops out... etc...). I will put this here for others who may not know about these distinctions.

> QM is based on special relativity

Not at all. QM makes no assumption about spacetime; you can formulate it without even mentioning space and time. As Scott Aarons puts it [1]:

Basically, quantum mechanics is the operating system that other physical theories run on as application software (with the exception of general relativity, which hasn't yet been successfully ported to this particular OS).

Historically, QM was developed in the context of Newtonian space + time; then came relativistic quantum mechanics, which is essentially about a fixed number of particles in a special-relativistic spacetime; and then came quantum field theory, where particles can be created and destroyed freely (because they are just excitations of quantum fields).

[1] https://www.scottaaronson.com/democritus/lec9.html

From your link:

>"Today, in the quantum information age,"

In what sense do we live in a "quantum information age"?

Edit:

Also, is there an example of a physical theory "running on the quantum mechanics OS"? That phrase doesnt make much sense to me.

Edit2:

Actually there is tons of stuff in here that seems off:

>"More often than not, the only reason we need experiments is that we're not smart enough."

I don't trust this guy to be explaining things to me correctly at all.

> In what sense do we live in a "quantum information age"?

You'll have to ask Aaronson what he means by that. :D I would guess he's thinking of technical applications which are attracting plenty of interest and funding (quantum computers, quantum communications).

> is there an example of a physical theory "running on the quantum mechanics OS"?

Sure: the entire Standard Model of particle physics. Stretching the analogy to the limit, because why not, QM is the OS it runs on, QFT is the framework it's written in, and the specific choices of gauge groups, fields and interaction terms are part of the application.

> "I would guess he's thinking of technical applications which are attracting plenty of interest and funding (quantum computers, quantum communications)."

As far as I know nothing usable has come of this. So what will he name the "age" when there are actual quantum computers being used by people?

>"the entire Standard Model of particle physics."

This is still so vague. I'm just trying to think about how some specific thing (eg, E = hv)[1] is linked to quantum mechanics as an OS.

[1]https://en.wikipedia.org/wiki/Planck%E2%80%93Einstein_relati...

>> "I would guess he's thinking of technical applications which are attracting plenty of interest and funding (quantum computers, quantum communications)." > As far as I know nothing usable has come of this.

Quantum communications are definitely a thing:

https://www.insidescience.org/news/china-leader-quantum-comm...

Quantum computing is still at the R&D stage, but if you are an academic, that pretty much defines what "age" you're in:

https://www.scottaaronson.com/blog/?p=2620

> This is still so vague. I'm just trying to think about how some specific thing (eg, E = hv)[1] is linked to quantum mechanics as an OS.

I think the analogy makes sense in terms of what builds on what. You can build an application on top of an OS, you can't build an OS on top of an application.

With something like "E = hv" you are looking at an application; it's expressed in terms of kinematic concepts, none of which is intrinsic to QM:

https://en.wikipedia.org/wiki/Mathematical_formulation_of_qu...

Or take the stefan-boltzmann law: https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law

In what sense is it "an application running on the quantum mechanics operating system".

This is quantum mechanics:

https://en.wikipedia.org/wiki/Mathematical_formulation_of_qu...

To go from that to something like Planck's law, you need to add states, observables and dynamics (things like photons, energy, temperature). Those are specific to your application.

Yea, so quantum mechanics is a set of assumptions. From those assumptions + some other "auxiliary" ones you can derive stuff like the stefan-boltzmann law that makes predictions about the world. Those predictions can then be compared to observation.

I just can't map that understanding to this OS analogy.

I guess then the article should have referred to relativistic quantum mechanics in the first place. Why bring non-relativistic QM up in the article about time?

Side note: I love Nautilus’s design, and their overall mission.

I really wish they would ship me the magazines I paid for, though.

They're desperately short of money, did you see that email from them a few weeks ago?

All my emails from them have been about money.

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