About 11 p.m., August 17, 2013. Played piano a little tonight after not
playing for months and months. I hope to
get back to it, and then get better at it, soon!
What a normal person would say upon hearing that the
uncertainty principle prohibits an arbitrarily precise measurement of both
position and velocity is, “well, something that’s moving doesn’t have a
position associated with it, because it’s moving! So of course it’s moved on from where it was
when you started to measure its position!”
I was just reading in “Quarks: The Stuff of Matter” by Harald Fritzsch, p.
9, when that thought occurred to me.
Fritzsch says, “In a certain sense, the notions of velocity and location
are complementary.”
Now the extremes of location and velocity in
combination that we can imagine are: a particle at rest (all location, no
velocity) and a particle with, somehow, velocity but no location.
The idea of a "particle" is the idea of a dot, like the period at the end of this sentence. So in this extreme case--imagining a definite location and zero velocity--the uncertainty principle’s prohibition on knowing the particle’s velocity is exactly zero calls into question the very idea of a particle.
The other extreme case would be a moving particle, and the more rapidly moving it is, the more extreme it is. Experimentally speaking, you can still locate it at a particular time by
bouncing a quick flash of light off it, but in the quantum realm, it recoils slightly when you do. Theoretically speaking, if you
know its equation of motion and its initial location and velocity, a graph can be drawn of its position (location,
location, and later location) as a function of time. But the uncertainty principle prohibits knowing with arbitrary or unlimited precision both it's initial location and velocity (or momentum, really).
This extreme case of no location is the more difficult to
imagine, but is approximated by a light wave, which is said to have zero rest mass because it only exists in its traveling-at-the-speed-of-light state. Actually, this is one reason we should be
more precise in talking about the uncertainty principle & discuss location & momentum,
rather than location & velocity, because the uncertainty principle DOES apply to light (photons), in
spite of the fact that we can measure the velocity of light with a precision
not prohibited by the uncertainty principle.
When we measure “c” (speed of light), we aren’t measuring “p” (momentum),
which is, for electromagnetic waves,
p
= E/c = hν/λν = h/λ.
E = energy, h = Planck’s constant, ν =
frequency, λ = wavelength
12:10 p.m. Sat. 26 Oct. 2013 Reverse time so that Big Bang is Big
Collapse—this is a commonplace thought experiment. But how do we know how gravity would really
behave? This thought occurred to me
after I read Sean Carroll’s sentence “Now let’s run the movie backward,” on page
49 in his From Eternity to Here book.
But there is really nothing in physics that corresponds to running a
movie backwards, because the observer is still going forward in time while he
watches the movie going backwards. He or
she.
But, a few pages later—surprise—this is pretty much
what Sean says, that it isn’t going to show (in the movie) what we would
expect, which would be galaxies dissolving into some other, more homogeneous,
matter. Instead, he says, “Growth of
structure is an irreversible process that naturally happens toward the future,
whether the universe is expanding or contracting. It represents an increase in entropy.”
Before he says that, he says this about the
contraction: “Imagine that we lived in a
universe much like our current one, with the same kind of distribution of
galaxies and clusters, but that was contracting rather than expanding.” So, my mistake! This is on page 53, and isn’t the same as the
“movie run backwards” scenario-ho-ho of p. 49, which was actually his way of
getting back to the Big Bang singularity.
The same old analogy! But he more
or less makes my point, and gives it credence, by saying a contracting universe
that is like ours would experience an entropy increase. That is really all we can imagine when we
talk about “reversing time” from here, from our current (initial, for collapse)
conditions.
(End of Journal – next page contains the end of my
eight pages of notes about Dallas trip in June, written backwards from the last
page in the journal, a case of writing going backwards in the book, but not of
“writing backwards.”)
Sunday 9:15 a.m. 24 NOV 2013 About 30° & overcast. This is from my other journal, the non-scientific one, Sept 10 or 11 2012:
Hidden Symmetry
I got up in the middle of the night on Sunday—early Monday mornin’—to write down the words above. Then later on in the day—wait, it must have been Sat-Sun middle of night, Sept 8th and 9th—later on I opened the Subatomic Physics text, and I encountered those exact words! They are on p. 370 in the section on Massive Gauge Bosons. Hidden symmetry is just one way to refer to the case where the Hamiltonian for the interaction “retains the full symmetry” and only the ground state breaks it. It can occur when “the ground state of the Hamiltonian is degenerate; the choice of a particular state among the degenerate ones then breaks the symmetry.” This stuff ought to be written in my other journal, my scientific one.
(Done. "Hidden symmetry" in theoretical physics, by the way, is already as common as pig tracks, so this was no great revelation of mine. Usually instead of calling it hidden, physicists call it broken. My idea of hidden symmetry would be that the current physics idea of symmetry is what is broken.)
Saturday 30 November 2013, 10:15 a.m., sunny with the
mercury at about 52° (as they used to say).
To continue where the last entry in my previous journal (physics
journal, October 26 of this year) left off, where I said “all we can imagine
when we talk about ‘reversing time’. . .”. Well, I have to correct that to say we can imagine whatever we want, but from the
point of view of the whole universe, watching a movie run backwards as a way modeling
the reversal of time is nonsense. The
observer of the movie is still going forward in time. Watching a segment of a movie where someone
walks backwards would not tell the observer whether that someone was really
walking backwards or the movie was going backwards (let’s assume the feet, which might be a giveaway,
aren’t visible in the frame). But the
movie observer knows the movie is being run backwards when an egg is
unscrambled and returned to its shell, or a diver comes feet first out of a
swimming pool and returns to the diving board.
Thought processes, neurons firing, biological processes and time
itself—all of these are still going forward as usual for the movie
watcher. That’s all I’m saying. And that’s all I can manage to think of
because it all seems beyond my rapport with the subject at the moment.
