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https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t636.2
x6YWpe9xHMg
maximum or some critical point rather than the minimum? The answer is you don't, you don't know
636.2
642.04
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t642.04
x6YWpe9xHMg
that, in fact that's fine, a path where the action was locally maximized would be a perfectly good
642.04
648.68
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t648.68
x6YWpe9xHMg
solution to the equations of motion. The problem is that's what not what appears in nature and the
648.68
653.56
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t653.56
x6YWpe9xHMg
reason why is you can easily make the action infinitely big, right, just like jiggle infinitely
653.56
659.64
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t659.64
x6YWpe9xHMg
fast very, very, very quickly on very, very small timescales you can get as big of an action as you
659.64
665
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t665.0
x6YWpe9xHMg
want, it's kinetic minus potential, just make your kinetic energy really, really big. So practically
665
671.72
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t671.72
x6YWpe9xHMg
there is no such thing as a maximum of the action, it can be infinitely big, there is such a thing
671.72
677
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t677.0
x6YWpe9xHMg
as a minimum at some finite value, that's where the actual paths are, that's why it's the principle
677
682.44
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t682.44
x6YWpe9xHMg
of least action, not just the principle of stationary action, but in principle as it were,
682.44
687.72
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t687.72
x6YWpe9xHMg
the principle could say any, any point where delta s delta path equals zero is a perfectly good
687.72
693.56
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t693.5600000000001
x6YWpe9xHMg
solution to the equations of motion, formally speaking. This also leads us to the following idea,
693.56
700.2
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t700.2
x6YWpe9xHMg
even if you can rule out maxima, you can certainly have functions where, here's another function f
700.2
707.4
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t707.4000000000001
x6YWpe9xHMg
of x versus x, what if I have a function that looks like this, where there's lots of minima
707.4
714.6
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t714.6
x6YWpe9xHMg
locally, there's a sort of, I didn't draw it very well, but probably this point is the actual minimum,
714.6
719.8
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t719.8000000000001
x6YWpe9xHMg
but this point and this point and this point all seem to be minima locally, right, you're in the
719.8
726.68
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t726.68
x6YWpe9xHMg
bottom of a little valley, and in fact at every one of these points, d f dx equals zero, there and
726.68
735.24
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t735.2399999999999
x6YWpe9xHMg
there and there and there and there. So I can draw zero better than that, I think. So what about those
735.24
745.4
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t745.4
x6YWpe9xHMg
points? You know, can we imagine that we might live there? Yeah, you can, in fact that's no problem,
745.4
751.16
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t751.16
x6YWpe9xHMg
whatsoever. Think about a particle in a box. So here's, now this is not space time anymore, this is
751.16
757.32
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t757.3199999999999
x6YWpe9xHMg
space and space. So here's x and y, okay, a box, two dimensional box. And I have a particle that
757.32
763.88
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t763.88
x6YWpe9xHMg
starts here. So this is x naught at time t naught. And I say I want the particle to get to here,
763.88
770.76
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t771.48
x6YWpe9xHMg
point x one at time t one, okay, and maybe y is also different for these two different things.
771.48
778.2
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t778.2
x6YWpe9xHMg
So clearly, there is going to be a path that looks like this, you just go straight across,
778.2
783.72
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t784.5200000000001
x6YWpe9xHMg
and you go at some velocity. So given that when you leave, you leave a time t naught,
784.52
789.56
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t789.5600000000001
x6YWpe9xHMg
and when you arrive, you arrive at time t one, there will be a correct velocity. So the principle
789.56
795.48
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t795.48
x6YWpe9xHMg
of least action will find that correct velocity for you. We'll tell you how fast you need to go
795.48
800.28
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t800.2800000000001
x6YWpe9xHMg
from there to there. But that's not the only path that would get you there. If you went more
800.28
805.56
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t805.56
x6YWpe9xHMg
quickly than that path, you would not go there because you would reach there and then bounce back
805.56
810.92
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t810.92
x6YWpe9xHMg
by the time you reached t one. If you went more slowly, you wouldn't get there in time.
810.92
814.84
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t815.4799999999999
x6YWpe9xHMg
But you can bounce off the wall at the correct angle. So this could be your path. If you move a
815.48
822.44
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t822.4399999999999
x6YWpe9xHMg
little quickly, it's a little farther path. But if you move more quickly, so you have a higher
822.44
826.6
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t826.5999999999999
x6YWpe9xHMg
initial velocity than the yellow path, put an arrow on the L path also, then that orange path
826.6
832.84
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t832.84
x6YWpe9xHMg
is perfectly allowed. That is something that could start you at x naught at t naught and get you to
832.84
837.96
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t837.96
x6YWpe9xHMg
x one at t one. What's wrong with that? Well, the answer is nothing is wrong with that. That's a
837.96
842.68
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t842.6800000000001
x6YWpe9xHMg
perfectly good path. And the principle of least action allows you to take it. So that is exactly
842.68
849.16
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t849.1600000000001
x6YWpe9xHMg
this situation. This yellow path is one of the points, which is a minimum of the action. This
849.16
856.04
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t856.04
x6YWpe9xHMg
orange path is another local minimum of the action. So the set of trajectories that satisfies
856.04
863.32
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t865.4
x6YWpe9xHMg
delta s, delta path equals zero, those give you all the allowed paths and they would all
865.4
870.92
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t870.92
x6YWpe9xHMg
be found by this method. So you see that there's a little bit of a disadvantage, maybe, to the
870.92
877.64
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t877.64
x6YWpe9xHMg
principle of least action versus the Newtonian-Loplossian way of doing things. The Newtonian-Loplossian
877.64
883.4
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t883.4
x6YWpe9xHMg
way of doing things gives you a unique answer almost always. There's some tiny little caveats to
883.4
889.72
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t889.72
x6YWpe9xHMg
that which we may get to later. But starting from a single point with a single position and a single
889.72
894.52
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t894.52
x6YWpe9xHMg
momentum, you just chug forward in time and you get a unique answer, minimizing the action between
894.52
899.64
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t899.64
x6YWpe9xHMg
two points at two different times could give you multiple answers. Maybe you consider that a bad
899.64
904.44
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t904.4399999999999
x6YWpe9xHMg
feature because you don't get a unique answer, but maybe it's good because you get a whole bunch of
904.44
907.64
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t907.64
x6YWpe9xHMg
good plausible answers. That's just how it is. That is allowed completely consistent by the principle
907.64
913.16
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t913.16
x6YWpe9xHMg
of least action. Good, I did that. I did that. So the last thing I wanted to mention sort of as
913.16
919.48
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t919.48
x6YWpe9xHMg
in a cleanup vein is how much information is required. Oops. Because I said that it was the same amount
919.48
931.8
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t931.8
x6YWpe9xHMg
in the Newtonian point of view versus the least action point of view. So if this is x, this is t
931.8
937.56
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t937.56
x6YWpe9xHMg
again. One way of doing it is you start here. This is t0. This is t1. I'm not a very well drawn t1.
937.56
947.72
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t947.7199999999999
x6YWpe9xHMg
Sorry about that. So you say you've been there. This is x1, t1, x0, t0. And I said, look, in the
947.72
959.96
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t959.96
x6YWpe9xHMg
Newtonian way, you would give me x0 and p0 at this initial time. In the least action way,
959.96
969.48
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t973.24
x6YWpe9xHMg
you would give me x0 and x1. So you give me the initial location and the final location. You don't
973.24
980.36
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t980.36
x6YWpe9xHMg
give me any velocities or any momenta at all. So I said it's an equal amount of information.
980.36
984.76
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t984.76
x6YWpe9xHMg
This looks like a one-dimensional line that the particle lives on, but if it lived in three dimensions,
984.76
989.4
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t989.4
x6YWpe9xHMg
there would be three pieces of information, three dimensions for the position and also three for
989.4
994.12
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t994.12
x6YWpe9xHMg
the momentum. So it still matches in both cases. But the question was asked, yes, but what about
994.12
999.8
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t999.8
x6YWpe9xHMg
the time? It looks like here you give me t0. And here you give me both t0 and t1. So that doesn't
999.8
1,007.88
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t1007.88
x6YWpe9xHMg
look quite fair. I get what you're saying, but it's not really an issue. Of course,
1,007.88
1,013.48
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t1013.48
x6YWpe9xHMg
in the Newtonian point of view, you start with x0 and p0. And then you get the entire path at all
1,013.48
1,018.76
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t1018.76
x6YWpe9xHMg
times. In the least action point of view, you get between t0 and t1. But I could still ask the
1,018.76
1,026.44
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t1026.44
x6YWpe9xHMg
question from the Newtonian point of view, given x0 and p0, given my starting position and velocity,
1,026.44
1,033.16
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t1033.72
x6YWpe9xHMg
where would I end up at t1? If I started at t0, where would I end up at t1? That is the question
1,033.72
1,040.84
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t1040.84
x6YWpe9xHMg
being answered by that point of view. And the least action principle, that process, formalism,
1,040.84
1,047.08
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t1047.08
x6YWpe9xHMg
answers the same question. Given I started at x0, at t0, and I want to end up at x1 at t1,
1,047.08
1,052.76
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t1052.76
x6YWpe9xHMg
what is the path I take in between? So secretly, it is exactly the same amount of information,
1,052.76
1,057.72
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t1057.72
x6YWpe9xHMg
either way. Don't worry about that. Okay. Now we get into more specific questions
1,057.72
1,062.92
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t1064.6799999999998
x6YWpe9xHMg
that were asked in various places. You can ask questions either in the YouTube video or on the
1,064.68
1,068.76
https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
x6YWpe9xHMg-t1068.76
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blog. You can try to ask questions on Twitter, but I might forget them. It might be hard to trace
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https://youtu.be/x6YWpe9xHMg
The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
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down. When I mention the blog, by the way, I'm embedding all these videos at preposterousuniverse.com
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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slash blog. This is my blog that I've kept for many, many years. Right now I'm using it as a
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
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place to put these videos. So you can ask questions there. There is actually the best place to ask,
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
2020-04-12T15:32:41Z
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because there's many more comments on YouTube that are not just questions. Okay. So here's a
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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question. Why? This is the kind of question I like. People asking, why is the action
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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S equal to the integral of kinetic minus potential energy? Oops.
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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And in particular, the kinetic energy is one half mv squared. Potential energy is just some
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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function v of x. Why is that the action rather than something else? So the glib and completely
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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100% true answer is that's what works. That is the formula that actually gives us the behavior
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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of particles in the real world for particles like a point ball rolling down a hill or something
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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like that. Okay. But what you're really asking then is, well, is there any principled reason why
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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I couldn't consider other things? Why couldn't consider the velocity cubed or the velocity times
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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the position or something like that? But the answer is those would give you different laws of physics.
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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This is the form of the action that gives you Newton's laws, f equals ma, and then the various
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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definitions of what you mean by f for the electromagnetic force or for the gravitational force or whatever.
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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This is the right kind of action. But you're allowed to consider other kinds of action. In
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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fact, let me tell you, let me reveal you a secret, not really a secret. Let me reveal you a true
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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fact that is well ahead of where we are in this discussion. One of the interesting things about
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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this least action way of doing it, one of the reasons why it's interesting, even though at the
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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end of the day, it just gives you back Newton's laws, is that when you get to more advanced,
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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more complicated, more subtle theories of physics, like we have in quantum field theory,
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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it becomes much easier to write down an action than it does to write down equations of motion.
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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And I can tell you why that is. So here we wrote down the action as kinetic energy minus potential
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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energy for a particle moving along a line. We will later on, god willing, be later talking about
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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field theory. So rather than talking about a particle at some position, here is space.
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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And this is time again. Remember, always label your axes. There's so many professional scientists
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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who will draw plots and they know what the axes are, but they don't tell you. So give me a hard
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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time if I don't label the axes. In field theory, the fundamental objects are not particles with
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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locations. They are fields like phi, it's a typical Greek letter that we use for a field,
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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and phi has a value at every point in space and at every moment of time. So there's phi at that
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The Biggest Ideas in the Universe | Q&A 3 - Force, Energy, and Action
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location, phi at this location over here, etc. It's a, that's what a field is. Unlike a particle,
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