existence

Recently I have been ponder about the meaning of "existence". No, I am not asking what the purpose of life is (which I consider a meaningless question). Rather, I am try to accurately define the meaning of saying "X exists."

When a person says "the table exists," I can understand this as an attribute of this table. The attribute "existence" in this case is true. However, I don't think this is reasonable: such an abstract attribute of an item (at least this is one way I understand "existence") also seems to be meaningless to me.

I think the real meaning of "existence" should be defined as subset operator. In other words, X exists if and only if X is a subset of the universe at a particular time. Existence is always a time-dependent boolean quantity. If anything is not part of the universe, then it is by definition non-existent.

Now if I press the question further: "how do I define the universe?" I can reuse the definition of physicality (previous post). Physical things are part of the universe. Physical things, because they interact with other physical things, are typically testable, though it may not be practical to test.

Still, I'm not exactly sure if this analysis is correct, but this is how far I have managed to achieve.

stardust

There's a lot of ways to be amazed; here's one: everything that humans have ever touched is stardust.


Sometimes, it's still amazing whenever I think about it. Of course, astronomers are probably well aware of that, but recently I still got a minor amazement when I realized this to its full extent.

There are those times when I still wonder how the illusion of consciousness has been achieved, but I have never been able to get far. Nature is strange like that (or as someone else puts it, "preposterous").

There are still times when I lie in the bed awake thinking about this, but I don't know if it is even a valid question to ask.

winter break begins

It's winter here; it's been winter since September. However, beginning on Saturday, the official MSU winter break begins.

Last week and this week 'til Friday, I completed all my finals for my classes, which means all my classes are already completed by now. This gives me a lot of extra time than usual, since my typical day in this semester has mostly been about lab reports (you probably noticed that in my Tweets).

I do sincerely hope that I can do some more "work" (as in things I wanted to do during the semester but never got to them) during the break, and not just goof things up and waste my time reading too many feeds or something.

Anyway, that's all the stuff I have to "report". Have a good Winter Solstice.

faster than wind

Update: It looks like Mark has changed his mind. So it seems, that faster-than-wind travel is indeed possible. I'm awaiting Mark's detailed analysis of the problem.

On Word Munger, I saw this really tough physics problem (below is my rephrasing):

Is it possible for a machine to harvest energy from only wind, yet capable of travelling faster than wind, yet in the same direction as the wind?

So far I haven't figure out if it's possible. Over at Word Munger, there is an argument going on between Dave and Mark, and I haven't been able to tell who is right yet.

Under "normal" conditions, a cart with a sail can't move faster than the wind speed; Dave argues that with the correct setup, it is possible to move faster than wind.

The counterintuitive part is that if the cart moves faster than the wind, the relative velocity of the wind becomes negative, resulting in a drag instead of a push. Yet somehow Dave is able to mitigate this by allowing the wheels to thrust the cart with a propeller. I'm not sure if the latter part is possible, since it feels like a "pull oneself out of a swamp with one's own hair" kind of problem. How can a wheel thrust itself? This is one thing I don't understand.

I wanted to come up with a mathematical model/equation that describes the cart's motion (in a simple way), but so far I haven't been able to do so because I don't know how propulsion thrust depends on rotational speed, nor do I know how wind thrust depends on relative wind speed. I might make some linear assumptions, but those are only assumptions.

If anyone has any idea about this, let me know.