All Kinds Of Thoughts About A Bucket Of Water And The Universe


I should clarify I mean the bucket contains water, and is itself in the universe. If this is not understood then I will be confusing.

Newton’s Bucket is one of the innumerable great physics problems involving buckets. By innumerable I mean two. The other one is the problem of how many buckets you can place over the head of a person sleeping in physics class before they startle awake. But this problem is of only historical interest anymore. Now that they have cell phones students don’t sleep in class, or anywhere else. This has helped them reach the level of maturity where we’re all tired and anxious. That surely helps.

So this is the other great bucket-based physics problem. And the fun thing is that you can work on it without having a bucket of your own. You don’t even need your own Newton, which makes things easier on all of us. First, imagine if you had a bucket. If you really do have a bucket, your imagination is either quite vivid or it’s not good at all. I don’t have a preferred interpretation. You can fight it out with your friends. Make sure to bring up the time they volunteered at the improv night and froze up on stage. That will surely help.

But take your bucket, imaginary or not, and put some water in. You can get water by imagining that you’ve burned some amines and filtered out the carbon dioxide and nitrous oxides. Or you can use the tap if you aren’t any fun. Imagine spinning the bucket, though. As you twirl it around, your arm gets very tired and, if you don’t stop, it falls off. So we maybe imagine hanging the bucket from a rope or a chain that can twirl around without being your arm.

Bartender: 'Here's one. How many theoretical physicists does it take to change a light bulb?' Lard: 'No idea, Phil.' Bartender: 'Two! One to hold the light bulb. The other to rotate the universe.' The gnome who's there with Lard looks horrified by the punch line.
Keith Tutt and Daniel Saunders’s Lard’s World Peace Tips for the 10th of April, 2019. It’s a surprisingly timely comic strip given my subject this week, and it’s completely on-topic if you don’t actually read it! Or if you wonder how this advances the cause of world peace.

The question is: while you’re spinning the bucket, how do you know the bucket and water are spinning? How do you know they’re not actually staying still while the entire universe spins around them, like the way it works when you’re riding a carousel? For us this is easy to answer. As the bucket spins, it spills water onto your socks. This makes you growl and set the bucket down. You go to change into oh, it turns out those were your last clean socks. Great. Now the day is spilled. You mean spoiled, but it’s spoiled by being spilled, so maybe they’re the same word after all and just look different and mean different things. Anyway your setting the bucket down settles the matter. If the whole universe were spinning instead, it would have to be that your socks spilled into the water. And you know that didn’t happen, unless you stepped into the bucket.

That’s the practical matter. Now imagine this, though. What if there were nothing in the universe except the bucket and the water and the chain it hung from? Then how would you know it was the bucket and water spinning instead? And this is the question that makes cosmologists say “whoooooah” to each other. Meanwhile the other people in the physics department? The ones working on, like, the dispersal of shock waves in rarefied fluids near a phase transition? They’ll say things like, “Yeah, they’re not with us” and “that person with the physics degree and the post as physics professor with an office in the physics department is … uh … we’re going to say in Evo Psych.” The evolutionary psychologists, happy to have someone talking about them in a non-derogatory way, agree.

But this does nothing to answer the question, which we have to do for some reason. So if there was almost nothing in the universe. There’s no distant galaxies. No planets. No things that wiggle. No pillows with flower prints. No battery-powered plastic candles. No nothing except this bucket and this water, how would you know if it were spinning? And the answer is that you don’t know, because you don’t exist. Not unless you’re either the bucket or the water. And we can be sure you’re not the bucket, not with your sense of dignity.

Can we be sure you’re not the water? This is a harder question to answer. To say for sure that you’re water would require pressing yourself into a sponge, pulling back out, and seeing if you can’t. But as the question set out, there are no sponges in the universe. So therefore there’s no way to do this experiment and thus tell.

And so we see the importance of Newton’s Bucket. Thanks to it we understand how fortunate we are to live in a world with sponges, as we would otherwise have no knowledge of which things were spinning. This surely helps.

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After Our Rabbit’s Holiday


“So you’ve been a bit of a terror, by reports,” I said to our pet rabbit. He was looking at the open pet carrier, and considering whether to punch it.

“They were desperate times,” he finally pronounced.

“They were times at your vacation cottage.” This would be my love’s parents’ house. They watch our pet rabbit when we have to be away more than a day. Our pet rabbit can’t be left unattended that long, because he’ll run up long-distance telephone calls. The funny thing is they’re not even calls that would make sense, like ordering stacks of particularly tasty hay. It’s like he just gets carried away with the fun of dialing. In many ways our pet rabbit is a little kid, except that he doesn’t give us colds or tell us complicated and rambling stories about what happened in school.

“There were dogs chasing me!”

“I know those dogs. They’re four years older than the letter `W’.”

“So they’ve had time to practice their fiendish ways!”

“They don’t have fiendish ways. They’re barely up to falling down anymore.” He sneezed, because somehow our pet rabbit sneezes, and then turned that into a snort. “They haven’t even been growling at me because they can’t work up the energy for that anymore.” And this is true. When I first started visiting my love’s parents, the dogs would take turns barking furiously at me, because they were afraid that if they didn’t, I might go on existing. Eventually they would settle down, only for one or the other to suddenly realize that I was still a thing that existed, so they had to go through it all over again. Since then, sadly, the dogs have gotten more frail. They’ll wander up to me and mutter a half-articulated hwurmf. I tell them that’s very good barking and then they collapse on the floor where they are. I’d pat their heads if that didn’t seem like taunting.

Our rabbit put his paws together and shoved on the front of his carrier, a traditional rabbit way of expressing the concept “I want this shoved over there a little”. It works better on hay and towels and light vegetables. I picked him up by his hind legs and shoved him in the carrier, a traditional rabbit-keeper way of expressing the concept “if you won’t go in I’ll just put you in”. He turned around and punched the carrier’s bars.

Finally he said, “I can scare dogs away.”

“You can scare those dogs away. They’re very timid dogs.”

“I didn’t even have to bite and the bigger one ran away!” The dogs are the same size, but perhaps there are rabbit ways of classifying dogs I don’t understand.

“That dog’s been scared away by clouds. You’re not saying you’re just as ferocious as a cloud, are you?”

“Bring me a cloud and I’ll see who scares who!”

“You’re figuring to make a cloud quiver its knees? What has got into you?”

“I had to spend forever fending off dogs!”

It struck me: the “larger” dog came up to the edge of our rabbit’s pen before running away, while the “smaller” one was too afraid of the interloper to get that close. By “running” I mean “kind of shambling about in a way that isn’t technically falling over most of the time”.

“Luckily,” he said, “I know what to do with dogs.”

“You know what to do with those dogs. You’re an expert at existing.”

“I spent my whole life getting ready to exist!”

Our pet rabbit, partly standing --- paw resting on his exercise pen's frame --- while he nibbles at a tree branch.
Our pet rabbit, existing, with panache.

“You could be in trouble if you had to face other dogs, you know.”

He almost stopped wriggling his nose a moment. “What other dogs?”

“You know there’s more than two dogs in the world.”

“No, I heard them both.”

“Did you ever notice the dogs going over to the window and barking like crazy, then stopping and hiding from the window?”

He nodded, which is the sort of thing that involves a lot of ear-flapping. “When they forgot where I was!”

“No, that’s when they saw there was another dog walking past, outside. They stopped when the other dog noticed them.”

He pushed the carrier door with one paw, letting his fingers melt through the bars. “So there are … 98 dogs in the world?”

“More than that, even. Some dogs they didn’t notice.” I figured it not worth mentioning some of the dogs were walked past the house several times, mostly on different days.

He sniffed. “More than 98 dogs seems like too many. Let’s get home.”

I don’t agree with him on the dog count, but getting home was what I hoped for too.