Time Out (of This World)

Kathleen V. Tatem

2022-09-01 00:05:20

Time Out (of This World)

In This Article

Time Out (of This World): The Physics of Time and How We Could Make Time Stand Still

 

Foundational questions, experimentalists, direction of time

As the foundations of physics becomes a specialization in philosophy and an interest of primarily theoretical rather than experimental physicists, experimental physics can have impacts in foundational questions that go unnoticed. This poem summarizes a thesis that bridges the gap between experimentalists and philosophers, showcasing a line of inquiry in the debate on the origin of the direction of time that is improved when in dialogue with experiment. First performed in Anna O'Brien's Irish Pub in Honolulu in 2017 and later in other venues throughout Hawaiʻi amidst public movements to protect Hawaiian sovereign lands from astronomy development, this narrative poem was inspired by Celtic rhyming traditions which stimulate community healing. As conflict swelled within and between the humanities, sciences, and the public in Hawaiʻi, this poem was designed to engage and equipoise polarized groups. Announcing the abundance of physical possibilities, alternative physics theories and philosophical interpretations, and unappreciated existing knowledge, this poem created a brief pause, a chance to imagine unanticipated outcomes. Read it out loud; it was written to be heard.

Strange,
Isn’t it?
If you start to
Think about it.
What are we, really?
What’s the fundamental nature
Of our experience?
Physics makes the mundane strange,
Makes everyday occurrences
Mysterious.
What hidden regularities,
Lie within our reach?
What are the patterns of nature?
What mathematics do we need?
A mathematical model of the universe,
That’s what physicists seek.
But as a philosopher,
I’m interested in what’s beneath,
The metaphysics within physics,
That is what I seek,
To read between the lines of the mathematics,
To have a metaphysical explanation,
Not just a useful mathematical equation.
There’s a philosophical problem in physics,
Called the problem of the direction of time.
It’s a problem right at the intersection,
Where physics and philosophy intertwine.
My goal tonight is to argue,
That this debate is something experiment can help decide,
And that if one idea is correct,
Then for an isolated system, we can stop time.
I’ll first describe the problem,
And then some proposed solutions,
Followed by a result from a recent physics paper,
And use it to argue how those solutions can be disproven.
Now consider, for example,
The mechanics of Newton.
To find the trajectories of objects,
A spatial coordinate system must be chosen.
Given the initial conditions,
Meaning the initial velocities and positions,
Of all the particles composing the system,
You know the whole trajectory,
The whole future, the whole history.
Use time as the variable,
And the positions of all particles at all times can be known with certainty.
Now certainly, you know this only works in theory,
Because really,
We don’t know the initial conditions
For a single spec of dust in this room,
Better yet for the entire universe in its entirety,
Better yet microscopically,
Which is what we’d really need to do,
If we wanted to reverse a physical system.  
Microscopically, there is reversibility.
This is what we call time-symmetry.
Just plug in “minus t,”
Just a negative value of time,
Into the equations of motion.
It reverses the direction of the velocity,
And you get the exact reverse trajectory.
Each particle will end up where it began,
Exactly where you’d expect it to be.
And now this really leads us to the question.
Since the laws of motion are time-reversal symmetric,
There are so many more physically possible paths than expected.
The laws of physics allow for miraculous happenings,
Things we’ve never detected,
Things like an egg un-cracking,
Like a broken glass un-shattering,
Like a beer un-spilling,
Like water un-splashing,
The problem is that nothing in the laws of physics explains why this weird stuff isn’t happening.
But for it to happen,
You would need a very particular force,
On every single particle,
Somehow directed upward from the floor,
Somehow to make the broken glass spontaneously restored.
But the spontaneous flow of energy like this isn’t something that we see.
It would require a decrease in entropy, 
The measure of disorder, of possibility,
The measure of possible microscopic arrangements beneath,
The macroscopic system that we see.
This is all summarized in the science of heat.
Derivable from statistical mechanics,
This is the second law of thermodynamics,
That the entropy of a system can only stay constant or increase,
If the system is isolated, meaning no energy enters or leaves.
This is a law that establishes a direction of time,
Because it makes irreversible processes well-defined.
In reversible processes, entropy remains the same,
But in irreversible processes, there is an entropy gain.
There are overwhelmingly many more ways,
That the subatomic particles could be arranged,
But on our level the system would still look unchanged.
It is possible for the glass to spontaneously recombine,
But this chance is so slim it essentially doesn’t matter.
There are so many more microscopic arrangements compatible
With the glass remaining shattered. 
But just counting a high number of possible microscopic states,
Doesn’t fully explain why a glass doesn’t un-break.
There is something else we need to postulate,
Which is that we can equate
The probability of each microstate compatible with a macrostate,
Meaning the chance of each microstate happening is the same.
Evolve time forward and it becomes probable entropy will rise,
But there is still a problem here,
Because of the symmetry in time.
Evolve time backwards, and entropy will still rise,
Contrary to experience - not something we want to hypothesize.
This is what led philosophers to take,
The origin of the direction of time,
As something that originates,
At the moment of the Big Bang,
The moment of the universe’s conception,
Where the fact that nothing existed before the bang,
Means you can only evolve time in one direction.
And so, in thermodynamics,
The problem of the direction of time can be solved,
If you apply the postulate that the probability of each microstate is the same,
Only at the moment of the Big Bang, and then let time evolve. 
But now consider the problem of electromagnetic radiation,
In which charged particles emit light when undergoing acceleration.
Consider mainly, the argument that was raised,
On how time-asymmetry arises from these waves.
In his paper with Einstein in 1909,
Walter Ritz argued that radiation is responsible for the observed asymmetry in time.
On his theory you don’t need to consider probability;
Time’s direction arises straight from electromagnetic theory.
If you’re a physicist this might sound confusing,
Because the laws of electrodynamics are time-symmetric, just like Newton’s.
Experimentally we only observe radiation go from past to future.
In the time-reversed scenario light should come collapsing in,
But this is something we never see in the lab,
And so the theory must assume a certain boundary condition.
The rule of thumb is to neglect the solutions where light goes from future to past.
They work just as well, but don’t question it, don’t ask.
Some would argue that that’s a scientist’s only task,
To predict the data they see in the lab.
Those neglected solutions are called the advanced fields,
And it's true, using them can feel really weird.
It seems to violate causality,
And creates a strange picture of reality.
It’s like saying the future affects how the past will be.
But actually, mathematically, for these types of equations,
The sum of two solutions also solves it the same.
You can solve the electrodynamics equations using a sum of incoming and outgoing waves.
This might seem to violate your intuition,
But it’s just a description for waves traveling in superposition.
Note that the sum of these solutions has time-symmetry.
Now I’ll describe a recent analytical discovery,
Made by Pardis Niknejadi, a physicist from University of Hawaiʻi.
She showed that if you assume the usual boundary conditions,
The laws of electrodynamics are violated or energy is not conserved.
She also hypothesized an experiment to look for the existence of the advanced fields,
The fields traveling in reverse.
And this would be a big deal,
Because it had been thought that these advanced fields aren’t really real.
I realized that this changes the debate in the direction of time,
Because some philosophers still argue against Einstein.
For example, one philosopher of physics named Mathias Frisch,
Argued that you should leave electrodynamics as it is.
He says that there is no problem at all,
Just take time-asymmetry in the radiation fields as a new fundamental law.
Others disagree, of course,
Particularly philosopher of physics Jill North,
Who argued that there is fundamental time-symmetry in radiation,
But the observed direction of time arises from probability, not the equations.
If you’re familiar with the argument on how we observe the cosmic microwave background radiation, or the CMB,
You’ll see that she argues similarly.
Advanced radiation fields are just something we no longer see,
Sort of like particle physics interactions that occurred when there was more heat.
Back in the early universe light could travel toward the past,
But as the universe cooled and expanded, this process didn’t last.
Frisch’s theory has already been analytically ruled out,
But so would North’s if Niknejadi finds advanced fields in the lab.
Something I should mention is that this is all about radiation into free space.
But what about radiation that is confined?
A study of radiation in a box actually won a Nobel Prize.
In an experiment by Serge Haroche,
He found in his lab the fields traveling in reverse.
An accelerating particle only radiated,
When the radiation waves were compatible with the edges of the box,
Which caused a bit of a shock.
It’s like the box had an effect on the particle’s internal clock.
How did it know what the edges of the box were shaped like?
It hadn’t radiated yet,
So there was no bounce-back of light.
The only explanation:
The advanced fields traveling back from the future carried this information.
But still, this discovery didn’t catch on generally.
It was thought that maybe just in confined spaces did radiation have time-symmetry.
Now I’d like to conclude with a hypothesis proposed to me by physicist John Madey,
That perhaps we could stop time, maybe.
You see, in Niknejadi’s paper, she favored a theory by Feynman and Wheeler,
Which is just as successful as these other theories but wasn’t taken seriously because it’s weirder.
If a tree falls in the forest and no one is around to hear it, does it make a sound?
You can ask an analogous question here and it’s pretty profound.
Will a particle radiate in empty space without bound?
Or does there need to be an absorbing material around?
Feynman and Wheeler answer “no” to this question.
They assume that even in free space,
For a particle to radiate,
There needs to be a thermodynamically absorbing boundary in the distance,
Or else no light will escape,
Even if a particle accelerates,
Or rather, it just wouldn’t accelerate,
Because in some sense,
It waits,
For information from those advanced waves
From the future,
To tell it about the boundaries’ shape.
Their theory is time-symmetric,
But the direction of time comes from,
You might guess it,
The probabilities in the thermally absorbing boundary in the distance.
Madey suggested,
What if we put something larger than a single radiating particle
Inside a superconducting cavity,
A cavity that inherently has no thermal absorption in its boundary?
What if we put an amoeba inside?
Would the amoeba age?
Or would we stop time?
What is the physical origin of the direction of time?
A philosophical question,
But one that future experiments could decide,
And where my intellectual journey will go,
I don’t know,
But I just let my memories of the future be my guide.

Works Cited


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