It's just that events that happen in that empty universe don't have causality, don't have memory, don't have progress and don't have aging or metabolism or anything like that. It's still part of the fundamental laws of nature even in that part of the universe. Physicists have no problem answering the question of “If a tree falls in the woods and no one's there to hear it, does it make a sound?” They say, “Yes! Of course it makes a sound!” Likewise, if time flows without entropy and there's no one there to experience it, is there still time? Yes. : So then, what is time in that universe?Ĭarroll: Even in empty space, time and space still exist. Because we depend on the arrow of time just for our existence. Because objects like us wouldn't exist in that environment. : So it’s a time that we don't understand and can't perceive?Ĭarroll: We can measure it, but you wouldn't feel it.
There's no future versus past, everything is equal to each other. So that static universe in the middle has time as a coordinate but there's no arrow of time. And then there's the arrow of time, which give us the feeling of progress, the feeling of flowing or moving through time. There's different moments in the history of the universe and time tells you which moment you're talking about. So does that mean that the universe at the center has no time?Ĭarroll: So that's a distinction that is worth drawing. From that, smaller universes pop off and travel in different directions, or arrows of time. : In this multiverse theory, you have a static universe in the middle. It's not, "Why did the universe begin with low entropy?" It's, "Why did part of the universe go through a phase with low entropy?" And that might be easier to answer. The Big Bang was not the beginning.Īnd if that's true, it changes the question you're trying to ask. I'm fitting in with a line of thought in modern cosmology that says that the observable universe is not all there is. We can’t say that the universe is part of something else. But with the universe, we don't have that appeal to make. It came out of a chicken, which is part of a farm, which is part of the biosphere, etc., etc. That's unusual," because you know that the egg is not alone in the universe. You don't say, "Wow, that's a low-entropy configuration. What's that?Ĭarroll: If you find an egg in your refrigerator, you're not surprised. But you theorize that there's something before the Big Bang. It's all because of conditions of the Big Bang. And it's interesting to think that connects directly to our kitchens and how we can make eggs, how we can remember one direction of time, why causes precede effects, why we are born young and grow older. I’m trying to understand cosmology, why the Big Bang had the properties it did. But why was it ever wound up in the first place? Why was it in such a weird low-entropy unusual state? It's like the universe is a wind-up toy that has been sort of puttering along for the last 13.7 billion years and will eventually wind down to nothing. But there's a missing piece to his explanation, which is, why was the entropy ever low to begin with? Why were the papers neatly stacked in the universe? Basically, our observable universe begins around 13.7 billion years ago in a state of exquisite order, exquisitely low entropy. So, Boltzmann understood that and he explained how entropy is related to the arrow of time. You'd be very surprised if a mess turned into neatly stacked papers. So, if you neatly stack papers on your desk, and you walk away, you're not surprised they turn into a mess. That's the second law of thermodynamics: Entropy goes up with time, things become more disorderly. Entropy is just a measure of how disorderly things are. He figured out this thing called entropy. The arrow of time is based on ideas that go back to Ludwig Boltzmann, an Austrian physicist in the 1870s.
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