I’ve been thinking a lot about physics lately. Perhaps it’s an unavoidable side-effect of all the energy I’ve spent clearing a wooded lot and building a high-performance house. On the other hand, it’s probably just because I’m a nerd about this stuff. While building, I’ve spent days and days listening to lectures and thinking about time and space, entropy and quantum mechanics. And for some weird reason, I can’t help thinking about my family and our life together when I contemplate spacetime and the origins of the universe.
This topic can get us deep in the weeds in a hurry and I want to explore all this later in much more detail, but for now I’ll try to keep it short and very simple.
From a common everyday perspective, it’s no surprise that the past is different from now is different from the future. Looking at a broken egg and a whole egg, common sense tells us which came first. No one thinks that the chaos of a broken egg could spontaneously somehow become a whole unbroken egg. This very simply is an example of The Arrow Of Time. It seems simple enough, but it is surprising from a physics perspective that there is an asymmetrical preference to this one dimension of our 4-dimensional universe (3 dimensions of space + the 4th dimension of time). There is no such preference when it comes to the other 3 dimensions.
Because this is surprising scientifically speaking, we need some sort of explanation… enter The Second Law of Thermodynamics. I said I’d keep this simple and I’m trying 😉
The Second Law of Thermodynamics gives us the idea of entropy. For the sake of simplicity, we’ll just say that entropy is the idea that in a closed system (no added energy) things tend to move from order to disorder. In other words, things tend to fall apart.
If I’ve lost you then I’m sorry. Let me say it this way: time only moves in one direction. It may seem like I’m being Captain Obvious here, but I find I often behave as if this isn’t the case. There are actual physical laws of the universe that explain this. There are no do-overs. We can’t go back and make different choices about time that has past. You can’t go back and choose to have something different for dinner yesterday. Again, I know it seems like I’m being obvious but I’m not sure this reality always sinks in.
Many of us are spending our time right now as if it’s gaining us time in the future, as if we could trade time while we’re young and our kids are around, for money and security and a similar quality and quantity of time later. We can’t. Entropy and the Arrow Of Time ensures that the time we spend now is gone, while we and everyone around us relentlessly grow older (gain entropy). Bummer, I know.
But here’s the good news! There is no such asymmetrical preference when it comes to the other 3 dimensions of space! Seriously, you don’t have to keep doing what you’re doing where you’re doing it. Time’s arrow says we can’t make alternate choices about the past but we can have freedom of choice about our location and activities in the future.
Now, maybe you’re perfectly happy doing what you’re doing where you are. That’s great! I was extremely happy living and working in a great city with awesome people for years while my kids were learning to walk and talk and ride bikes. For us though, in this moment when they are old enough to really study the world around them and yet young enough to help us see things with fresh eyes too… well, we’re obeying the laws of physics that tell us we won’t get a do-over on this moment.
So, as my personal hero once said: “And now, Harry, let us step out into the night and pursue that flighty temptress, adventure.”