In Germany 1865 physicist Rudolf Clausius He stated that heat cannot be transferred from a cold object to a hot object, if nothing has changed around them. Clausius came up with a concept he called “entropy” to measure this behavior of heat – another way of saying that heat never flows from a cold body to a hot object is to say “entropy never increases and never decreases” (See the picture of entropy and the emergence of turbulence).
seperti Rovelli Confirmed in chronological orderThis is Alone The fundamental laws of physics that can tell the difference between past and future. A ball can roll down a hill or bounce off its top, but heat cannot flow from cold to hot.
To illustrate, Rovelli took the pen and dropped it from hand to hand. “The reason this stopped in my hand is because it has some energy, so the energy turns into heat and warms my hand. The friction stops bouncing. Otherwise, if there is no heat, it will recover forever and I will not distinguish the past from the future. “
So far, it’s straightforward. That is, until you start thinking about what heat is on a molecular level. The difference between a hot object and a cold object is how agitated the molecules are: in a hot steam engine, the water molecules are excited, quickly deflecting and colliding with each other. The water molecules themselves are less agitated when they combine as condensation on the window glass.
Here’s the problem: When you zoom in on the level of, say, one water molecule colliding and bouncing off another, the arrow of time disappears. If you look at a microscopic video of this collision and then reverse it, it won’t be clear which direction is forward and which is backward. On a smaller scale, the phenomenon that produces heat – the collision of particles – is symmetrical over time.
This means that the arrow of time from the past to the future only appears when one takes a step back from the microscopic to the macroscopic, which the Austrian physicist and philosopher Ludwig Boltzmann first appreciated.
“So the temporal trends come from the fact that we look at the big things, not the details,” Rovelli said. From this passage, from a basic microscopic view of the world to a rough and rough description of the macroscopic world, this is where time comes into play.
“It’s not that the world is fundamentally oriented to space and time,” says Rovelli. When we look around, we see a trend where medium-sized objects have more entropy every day: ripe apples falling from trees, jumbled piles of papers.
While entropy seems inextricably linked to the arrow of time, it is somewhat surprising – and perhaps even confusing – that the only law of physics that has a strong time direction in it loses that direction when you look at very small things.
