
The crisis inside the physics of time - dnetesn
http://nautil.us/issue/64/the-unseen/is-it-time-to-get-rid-of-time
======
nyc111
> 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.

~~~
GW150914
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.

~~~
pdkl95
> 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).

~~~
furgooswft13
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.

------
lisper
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...](http://blog.rongarret.info/2014/10/parallel-universes-and-arrow-of-
time.html)

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

~~~
lostmsu
What is an "emergent property"?

~~~
cobbzilla
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.

~~~
doitLP
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.

~~~
fjdndidjd
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!

------
eafkuor
> 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!

------
carapace
> 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.

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

------
jeromebaek
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.

~~~
adrianN
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?

~~~
jeromebaek
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.

------
lostmsu
"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.

~~~
T-A
> 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](https://www.scottaaronson.com/democritus/lec9.html)

~~~
nonbel
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.

~~~
T-A
> 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.

~~~
nonbel
Or take the stefan-boltzmann law:
[https://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_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".

~~~
T-A
This is quantum mechanics:

[https://en.wikipedia.org/wiki/Mathematical_formulation_of_qu...](https://en.wikipedia.org/wiki/Mathematical_formulation_of_quantum_mechanics#Postulates_of_quantum_mechanics)

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.

~~~
nonbel
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.

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

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

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

~~~
byron_fast
All my emails from them have been about money.

