In the last week or so I read an interesting pair of books: Through Two Doors at Once, by author and journalist Anil Ananthaswamy, and The Order of Time, by theoretical physicist Carlo Rovelli. While I did find them interesting, and I’m not sorry I bought them (as Apple ebooks), I can’t say they added anything to my knowledge or understanding.
I was already familiar with the material Ananthaswamy covers and knew of the experiments he discusses — I’ve been following the topic (the two-slit experiment) since at least the 1970s. It was nice seeing it all in one place. I enjoyed the read and recommend it to anyone with an interest.
I had a little trouble with the Rovelli book, perhaps in part because my intuitions of time are different than his, but also because I found it a bit poetic and hand-wavy.
It seems presumptuous of me to think I know better than a highly trained award-winning theoretical physicist who has studied time throughout his career. Any opinions of mine should be taken with an entire salt shaker.
That said, I wonder sometimes if theoretical physicists (and deep thinking philosophers) don’t sometimes get lost in their own imagination. Sabine Hossenfelder has a book, Lost in Math, that argues theoretical physics has badly lost its way.
There is something of a stagnation in certain areas of physics, and it’s not hard to imagine sometimes that we’ve gone down a blind alley.
The vexing thing is that the alley (or rabbit hole) we’ve gone down is amazingly effective and matches all available data to very high precision. It’s hard to see where it could be wrong.
In Through Two Doors at Once, Ananthaswamy closes by using the book’s main topic — wavefunction collapse — as a metaphor for our (lack of) understanding regarding what’s going on.
There are many theories and ideas, but our waveform hasn’t “collapsed” into definite knowledge on the matter. (In this case, the wavefunction almost certainly reflects our ignorance.)
I like the metaphor. It seems to apply to several topics in physics.
For example, the exact nature of human consciousness: many ideas, but none have collapsed into definite knowledge.
Ananthaswamy’s metaphor directly connects with Rovelli’s book in that time is another aspect of reality that presents us with an as yet uncollapsed question:
Is time fundamental? Or does it emerge from some other process?
It is on this point that my intuitions about time conflict with Rovelli’s.
I maintain an old-school belief that time (and space) are fundamental — they are not comprised of smaller components and they do not emerge from some other system.
It’s obviously not “turtles all the way down,” so at some point you have to accept that some things just are. For me it’s spacetime and the quantum fields. I think that’s the basic fabric of reality.
There is an alternate view, going back to Leibniz, that time and space are just relationships, and there are modern theoretical views that time emerges from something else (for instance, entropy).
To be blunt (with full understanding I may also be wrong), I find these alternate views incoherent. I can’t find any sense in the idea that some other process “creates” time or that it “emerges.”
For one thing, the very idea of a “process” — or that something can “emerge” — requires time in the first place (according to Kant, we can’t even think about these things without assuming fundamental time).
For another, a relationship is an operator between two things. Distance, for example, is an operator that puts a number to the space between two points. It makes no sense to speak of distance without those two points in the first place.
An example Rovelli has used in interviews suggests that emergence doesn’t require time: He points out how flat the Earth looks to us, but from space its curvature emerges.
But note the implicit movement from a close to distant perspective. Or just note that first we speak of the close view and then we speak of the far view.
What I’ve found is that most discussions about timelessness always allow time to sneak in the back door. There is always a first this, then that scenario.
For example, from the footnotes, where Rovelli gets more specific about exactly how the “unnecessary” variable t (for time) is removed:
The general form of a quantum theory that describes the evolution of a system in time is given by a Hilbert space and the Hamiltonian operator H. The evolution is described by Schrödinger’s equation iħ∂tΨ = HΨ. The probability of measuring a pure state Ψ a time t after having measured a state Ψ′ is given by the transition amplitude 〈Ψ | exp[–iHt/ħ] | Ψ′〉. The general form of a quantum theory that describes the evolution of the variables with respect to one another is given by a Hilbert space and Wheeler-DeWitt equation CΨ = 0. The probability of measuring the state Ψ after having measured the state Ψ′ is determined by the amplitude 〈Ψ | ∫ dt exp[iCt/ħ]|Ψ′〉.
Note the phrasing: “after having measured”
Time always sneaks in the back door. (I’d also like to know more about exactly what C is in his equation.)
Kant found time to be a irreducible a priori intuition, and an internal one at that. We can’t think without a background notion of time. I think Kant got this one right.
Another plank in Rovelli’s argument involves how General (and Special) Relativity have scrambled our common notions of time.
Under SR, the idea of “now” becomes personal and local. Your “now” is not the same as anyone else’s “now.” The further away someone is, the more meaningless is the idea of a simultaneous “now.”
Under GR, the scrambling gets worse. Your feet aren’t experiencing the same “now” as your head because they are (usually) deeper in the gravity well.
We now have clocks capable of detecting the difference of a few feet or of walking speeds. Rovelli suggests at one point that what we feel as gravity is actually a seeking for the slower time of being deeper in the gravity well.
That every particle exists in its own timeline doesn’t, to me, require that time isn’t fundamental. It just means the fabric of spacetime is complex and twisted.
I’m more compelled by how every particle, despite having its own proper time, has essentially the same proper time as every other particle. By that I mean every particle’s “clock” ticks at the same rate — the fundamental passage of time.
This is a basic tenant of physics: that everything behaves the same regardless of your position or motion. All proper clocks tick at the same rate even if they appear to run faster or slower to relatively moving observers.
Besides the question whether time is fundamental is a question of whether time is quantized.
Whether these represent a quantizing of space and time is an open question. It’s possible they represent accessible limits. And it is true that assuming spacetime is smooth leads to some impossible math.
So current modern thinking (although there are exceptions besides yours truly) is that spacetime is quantized just like energy-matter. The search for quantum gravity mostly involves quantizing GR.
BTW: Rovelli is one of the founders of loop quantum gravity, one approach to quantizing spacetime.
A question I have involves how the quantum aspects of energy-matter reared their head a long time ago. There were things (like ovens) we just couldn’t account for, that had impossible results (like ovens melting into white-hot slag, which they clearly don’t).
We all but stumbled over quantum mechanics. For that matter, both SR and GR answered existing questions — apparent gaps in our understanding.
Where is that for quantum time or space? So far nothing we’ve seen gives us any pause. (Other than the assumption space can be infinitely small which leads to some weird math results.)
In the discussion of time, entropy is a key player. Some think time arises from entropy; I think that’s putting the cart in front of the horse.
I laughed out loud at one point that, to my eyes, said it all. He writes:
The conventional logic for interpreting this relationship is therefore:
time → energy → macroscopic state
Which I think is not just conventional but correct. Then he reverses it:
macroscopic state → energy → time
Which clearly is putting the cart in front of the horse. I had to laugh, because it’s exactly what I’ve always thought about emerging time being backwards, and here Rovelli waves his hands and proclaims it explicitly.
Entropy figures in Rovelli’s thinking, and he seems to give it center stage in a tragic play:
From the most minute events to the more complex ones, it is this dance of ever-increasing entropy, nourished by the initial low entropy of the universe, that is the real dance of Shiva, the destroyer.
I added a note to the text at this point: “This focuses on the Yin and ignores the Yang. Everything we are lies in the temporary increases of structure and order. Life uses the energy and emits waste entropy.”
To me, entropy is the result of the behavior of particles in time. It’s what happens in any physical system. It’s not the source of time.
It does, however, seem connected with the “arrow of time” — that despite the basic physics having no preferred direction — time marches forward due to entropy, it is presumed.
If one views the basic laws of physics as a wheel that can turn forwards or backwards (in time), then entropy is seen by some as a ratchet that forces it to only turn forwards.
But if entropy is an effect, then we’re left with the understanding of a fundamental aspect of reality: Time.
And it marches forward just fine on its own.
To be honest, I mostly just skimmed the last two chapters. By then Rovelli was wrapping up and had gotten (to my eye) particularly poetic and hand-wavy.
He seems to place a lot of weight on our perception of time, not so much as a filter preventing us from fully understanding it (which is certainly true), but as somehow involved in creating time.
He talks a lot about our “blurred” view of reality and how entropy is relative through that blurred view. I found myself repeatedly disagreeing with his assessment, although as I said up top, who am I to doubt the word?
Well, I’m just me, and I think what I think.
Stay timely, my friends!