What is time?
I’ve been reading a book called The Order of Time by Carlo Rovelli. What an interesting read. What I cover here are my interpretations. If and when I got them wrong, that’s my fault.
Time isn’t infinitely small
You can’t infinitely keep dividing a unit of time (a second, let’s say). Or at least, for a certain period of time short enough, the idea of time doesn’t apply any more. That gets to an idea of quantum physics, where there are definable “smallest” parts that don’t get smaller (a quant meaning a grain, it seems).
That reminds m of how the Greeks used logic to come up with the idea of atoms, several thousand years before we could tell that there are atoms.
Before now, I would’ve thought of time as something that could essentially be sub-divided without end. Rovelli states that the basic equations defining our world don’t have time as a fundamental factor. At most, it seems the difference in time passing is relative to two given objects. Time is local. There is no universal “time beat” that can be measured across the universe. Time is relative.
Time is local
I had previously heard about the fact that time passes a little faster up in an airplane compared with a clock at sea level. Einstein had theorised this, and it turned out to be indeed true.
Newer experiments have been able to show that a clock on a table, say, is going through time just a little faster than a clock down on the ground. Your feet, over your lifetime, will have experienced time that little bit faster than your head. This point is related to being on the mass of our planet. As earth travels through space, its mass effects the passing of time around it. Indeed, your own body does the same, but to a much lesser extent.
There is no universal “now”
I do find it hard to understand this. If you’re seeing a person next to you, indeed those quants of energy (photons, light) bounced off them very very briefly before those photons hit your eyes, and of course there’s time for your brain to interpret this information.
If you’re speaking with someone across the Atlantic on the phone, there are a couple of milliseconds between you. If you ask what they are doing “now”, that information can only reach you at the speed of light and not faster. With this distance, we can start to understand that a local “now” is at least detectable. But speak with someone on a planet that’s 4 light years away and you ask them what they’re doing “now”, that question becomes senseless (Rovelli argues that it’s not a valid question at this point). It takes 4 light years for your question to reach them (at least), and light years for you to get your answer. If you’re on earth, you’re not in the same universal “now” as the person on that other planet. There is no universal now. Now is relative.
On your feet sticking to the ground, rather than your body floating around, that’s a symptom of things being attracted to where time moves slower. I don’t know if Rovelli is arguing that gravity that we experience is a symptom of things really trying to move to where time is moving slower.
Heat is related to time
I said above that the fundamental equations that describe our universe don’t require time as a fundamental property. It seems that time delta – the difference in how I perceive time compared to another object – shows up as important. It’s the relative difference in time that can be truth, rather than there being a universal beat in the system.
The second law of thermodynamics seems to give direction to the arrow of time. I won’t claim to understand this, and correct me if I’m wrong, but entropy is the inclination toward disorder. Our universe had very low entropy at one point, and it’s continuing to increase in disorder.
Related to this point (somehow!) is that heat is the bi-product (or source?) of “work” that can be done within the universe. If you kick a ball, the ball slows down and stops, and heat is the bi-product of that process. Our universe is dropping in temperature over time, and there is less “work” that can be done within the system. It seems that heat can only go from a hot place to a cold place. Cold can’t go into a hot place. Heat disperses. It’s a one-direction process, and this is a fundamental rule that helps give a “direction” to time passing. I won’t pretend to understand how all these concepts tie together.
Time is our memory
1,300 years ago, Bishop Augustine of Hippo (later St. Augustine) argued that time is our perception. We have a perception of the past, the present and the future. However, we are always in the present moment, and we’re never anywhere else. If we’re always in the present, there is no such thing as the past. The past is a perception within us. It’s a trace of a past present in our memories and our awareness.
I wonder if this can help us get through periods of life that feel “long”. I might tell myself that “oh I’ve been stuck on this bus now for 2 hours and it feels really long”. But right at that very moment, I’m just sitting in a bus. Anything about feeling like how long it’s been is a perception I’m focussing on. If I’m on the bus for an hour or a day, at that very moment it’s just that I’m on the bus. What should it matter that past traces of the present indicate to my awareness that I’ve been in such a present for a long “time”?
For me, this helps give another perception of the Buddhist view of trying to stay with the “now”. I’ll always be in the present, and there’s no such thing as not the present. To try to escape the present seems to be fundamentally at odds with our universe, where there is only the present. That being said, it does seem logical to me that we do decide to act to change the present. If I’m standing outside in the cold, and I’m getting too cold, it would be stupid of me to decide to stay outside because “I only live in the present”.
Time is about events
This gives an extra emphasis to me on what “reality” is. Reality is the present. You can ruminate or worry all you want, but the present moment really is the reality. Over “time”, there are trends, and the present reality will be different to a reality that “was” before.
Rovelli, I think, argues that time happens with events or changes. The universe is change. If nothing ever moved or happened, there would be not time. But the universe is in endless flux. Time passes through physical real events. That’s at a quantum level, but seems to me to also apply to daily life. If you’ve had a jam-packed week, it can feel like a month. It’s a fact that life is change, and without change there wouldn’t be life.