Download I. Intrinsic and extrinsic properties

Physics, Metaphysics, & Other Nonsense
H.S. Hestevold
Handout 14
Spring 2014
Quantum Mechanics: Philosophical Concerns, Part I
I.
Intrinsic and extrinsic properties
Stephen Yablo writes: “You know what an intrinsic property
is: it's a property that a thing has (or lacks) regardless of
what may be going on outside of itself.”1 David Lewis writes:
A sentence or statement or proposition that ascribes intrinsic
properties to something is entirely about that thing; whereas an
ascription of extrinsic properties to something is not entirely
about that thing, though it may well be about some larger whole
which includes that thing as part. A thing has its intrinsic
properties in virtue of the way that thing itself, and nothing
else, is. Not so for extrinsic properties, though a thing may
well have these in virtue of the way some larger whole is. The
intrinsic properties of something depend only on that thing;
whereas the extrinsic properties of something may depend, wholly
or partly, on something else. If something has an intrinsic
property, then so does any perfect duplicate of that thing;
whereas duplicates situated in different surroundings will
differ in their extrinsic properties.2
How the distinction between intrinsic and extrinsic properties
should be drawn is controversial,3 but we will not involve
ourselves with this controversy. Rather, the distinction will be
developed informally, leaving us with a rough-and-ready
understanding of the distinction suitable enough for the purposes
of our discussion.
Roughly, an entity’s intrinsic properties are those
properties that it has independently of other things that exist.
For example, you have the intrinsic properties being human, being
conscious, being biologically female (or being biologically male,
1 “Intrinsicness”, Philosophical Topics 26 (1999), 479.
2 “Extrinsic Properties”, Philosophical Studies 44, 111-112.
3 For example, are an entity’s extrinsic properties its relational properties
(e.g. being the father of Marilyn Monroe, being larger than an apricot) such
that its intrinsic properties are its monadic properties (e.g. having mass,
being red hot, having a positive charge)? Are an entity’s intrinsic properties
its essential properties -- those properties it has at any time that it
exists? (This would suggest that an entity’s extrinsic properties are its non—
essential properties -- properties that the entity happens to have, but need
not have.) Are an entity’s intrinsic properties those properties that it would
have in common with any duplicates of that entity? (This would suggest than an
entity’s extrinsic properties are those properties that any of its duplicates
could lack.)
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as the case may be), and having a body with such-and-such mass.
That you have these characteristics is a function of you alone:
you would have these properties even if every other entity in the
universe disappeared. (If a mad scientist created a doppelganger
of you, the doppelganger would also have those properties.)
You have other properties, however, that don’t involve
yourself alone; these other properties in some sense depend on
other entities that exist. For example, you now have the
properties being a daughter (or being a son, as the case may be),
being a sibling (if you have a brother or sister), being an aunt
or uncle (if you have a nephew or niece), being a student at UA,
and weighing more than Hestevold’s dog. Your being a sibling (if
you are) is incidental: you would not have this property had your
parents not had at least one child other than yourself. You may
now lack the property of being an aunt (or uncle), but you will
acquire that property if you have a sibling who becomes a parent.
Had individuals never formed The University of Alabama, you would
not now have the property of being a student at UA.
A proton’s mass or charge would be among its intrinsic
properties; whether it is part of a hydrogen atom or boron atom
would be an extrinsic feature of the particle. Having a spin of a
certain direction is an intrinsic property of the electron (even
though its spin may be causally affected by entities other than
the electron). If spatial points do exist after all, then
presumably every spatial point has the same intrinsic properties
as any other spatial point; but spatial points would differ with
respect to their extrinsic properties (e.g. with respect to the
spatial relations that they bear to certain other spatial
points).
II.
A simple-minded explication of the double-slit experiment
Read Lawrence Sklar's description of the double-slit experiment in “The Quantum Picture of the
World” in SUP, 165.4-167; study Figure 4.2.
A.
Experiment #1: What happens when electrons are fired at
a double-slit wall with the right {R) slit closed? The
electrons form a strike pattern in front of the left
(L) hole that is evidence that each electron exhibits
the property being a BB like particle.
B.
Experiment #2: What happens when electrons are fired at
a double-slit wall with the L slit closed? The
electrons form a strike pattern in front of the R hole
that is evidence that each electron exhibits the
property being a BB like particle.
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C.
Experiment #3: What happens when electrons are fired at
a double-slit wall with the both slits open? The
electrons do not form BB-like strike patterns in front
of the two slits. Rather, they form an interference
pattern -- a pattern that suggests that electrons lack
the property being a BB-like particle.
D.
Regarding Experiment #3, what should we claim about a
given electron E between the time it leaves the
electron gun and the time it strikes the detection
screen? Does E reach the detection via the left slit?
The right slit? Both slits? Neither slit?
1.
Reminder: If X = Y, then X and Y have all
properties in common.
2.
"E traveled through the left slit to reach the
detection screen." In Experiment #3, electrons
that strike the detection wall apparently lack the
property being a BB-like particle. But Experiment
#1 suggests that those electrons that pass through
the left slit have the property being a BB-like
particle. So, E cannot be identical with any
particle that passes through the left slit.
3.
"E traveled through the right slit to reach the
detection screen." In Experiment #3, electrons
that strike the detection wall apparently lack the
property being a BB-like particle. But Experiment
#2 suggests that those electrons that pass through
the right slit have the property being a BB-like
particle. So, E cannot be identical with any
particle that passes through the right slit.
4.
"E traveled through both the left and right slits
to reach the detection screen." First, some would
argue that it is metaphysically impossible that a
single entity could wholly occupy two distinct
places at the same time. Second, if one places a
detector by each slit, one detector or the other
(but not both) will register every time an
electron is fired toward the detection screen and
makes it past the double-slit wall. So, there is
experimental evidence that no electron passes
through both slits at once. And there is no
evidence that a half-electron passes through each
of the two slits.
5.
"E traveled through neither slit to reach the
detection screen." This is not a viable option: if
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one blocks both slits, E would never have reached
the detection screen. So, unless one believes in
mystical teletransportation, E cannot jump from
the electron gun to the detection screen without
taking one path or the other.
6.
"Between leaving the electron gun and striking the
detection screen, E was in superposition:" Between
leaving the electron gun at time t and striking
the detection screen at time t*, electron E was
something that exhibited a mysterious mode of
being that did not involve E's having a particular
set of intrinsic properties at a particular time
and location. (It is false that E travels through
the left slit with the property being a BB-like
particle; it is false that E travels through the
right slit with the property being a NON-BB-like
particle.)
III. A simple-minded explication of two experiments4
Read Lawrence Sklar's description of the Stern-Gerlach experiment, 168.1-170.1; study Figure 4.4.
To simplify matters, abandon talk of spin, momentum, and the
like. Instead, let's talk about color and hardness. Assume that
every electron is either black or white [B or W]; and assume that
every electron is hard or soft [H or S].
A.
Color box. There is a color box that detects the color
of electrons: if a stream of electrons enters from the
west, all B electrons exit to the north, and all W
electrons exit to the east. Color determination is
repeatable: if color box #1 detects Ellie to be a B
electron, then color box #2 will also reveal that Ellie
is B. Note: The color box reveals nothing else about an
electron but its color; if an electron emerges from the
east, we know it is W, but we don't know whether it is
spinning up or spinning down, whether it is hard or
soft: one would need a spin box or hardness box to
detect those characteristics…
B.
Hardness box. There is also a hardness box that detects
the hardness of electrons: if a stream of electrons
enters from the west, all H electrons exit to the
north, and all S electrons exit to the east. Hardness
determination is also repeatable: if hardness box #1
detects Elton to be an S electron, then hardness box #2
4 See David Z. Albert, Quantum Mechanics and Experience, Ch. 1.
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will also reveal that Elton is S. Note: The hardness
box reveals nothing else about an electron but its
hardness; if an electron emerges from the north, we
know it is H, but we don't know whether it is spinning
up or spinning down, whether it is black or white: one
would need a spin box or color box to detect those
characteristics.
C.
D.
Experiment #4: Are color and hardness correlated? Is it
true that most W electrons are also H or that most S
electrons are B? Or, is there no correlation between an
electron's color and its hardness? To answer these
questions, put a color box in sequence with a hardness
box (and then vice versa). The results:
1.
If you take the B electrons that emerge from the
north of a color box and feed them through a
hardness box, half the B electrons will be H and
half the B electrons will be S.
2.
If you take the W electrons that emerge from the
east of a color box and feed them through a
hardness box, half the W electrons will be H and
half the W electrons will be S.
3.
If you take the H electrons that emerge from the
north of a hardness box and feed them through a
color box, half the H electrons will be B and half
the H electrons will be W.
4.
If you take the S electrons that emerge from the
east of a hardness box and feed them through a
color box, half the S electrons will be B and half
the S electrons will be W.
5.
The bottom line: by linking two detection boxes,
there appears to be no correlation between color
and hardness.
Experiment #5: what if one places a hardness box
between two color boxes?
1.
Step 1: Color box #1 produces a stream of 100% B
electrons and a stream of 100% W electrons.
2.
Step 2: Take all the B electrons from color box #1
and stream them through the hardness box. What
will happen? Just as before, the stream of B
electrons will generate a stream of 50% H
electrons and 50% S electrons. (Are the H and S
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electrons all B when they exit the hardness box?
One would likely assume that they are all B, but
we don't know: the hardness box sorts by hardness,
not by color. So, the only thing that we can
detect about an electron emerging from a hardness
box is that it is H or S; we can't also detect at
that time its color.)
3.
Step 3: You now experiment with the H electrons
that all streamed out of the north (i.e. B) exit
of the hardness box. You stream the H electrons
through the west opening of color box #2.
What results should you expect? Answering this
question seems obvious. We know that color
detectors are repeatably accurate: if passed
through a color box again and again, Ellie the
B-electron will be detected to be B again and
again. So, if color box #1 generates a stream of
all-B electrons, and if that stream of all-B
electrons is subsequently divided (by the hardness
box) into streams of H and S electrons, then one
would assume that that stream of H electrons, when
run through color box #2, would generate a stream
of B electrons exiting north and no W electrons
exiting east. This anticipated outcome is not what
happens…
The actual results. From the stream of H
electrons, color box #2 actually generates two
streams of electrons: 50% are B and 50% are W! How
can this be? Using only one color box and one
hardness box, we produced evidence that color and
hardness are independent properties of electrons.
Yet, given the three-box experiment, it appears
that detecting an electron's hardness can causally
affect the color of the electron: the second color
box generates two streams of electrons -- one
stream of B electrons and another stream of W
electrons! (Pause a moment to scratch your head.)
[Note: Are the B and W electrons all H when they
exit the color box? One would likely assume that
they are all H given that they all originated from
the north exit of the hardness box, but we don't
really know: the color box sorts by color, not by
hardness. So, the only thing that we can detect
about an electron emerging from color box #2 is
that it is then B or W; we can't also detect at
that time its hardness.]
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IV.
A simple-minded explication of a more complicated
experiment5
A.
The two-mirror apparatus. Imagine a square work bench.
A hardness box is mounted in the lower left (i.e.
southwest [SW]) corner of the bench; if a stream of
electrons enters through the west opening of the box,
hard electrons stream north following the western edge
of the bench, and soft electrons stream east following
the southern edge of the bench. A mirror at a 45°-angle
at the NW corner changes the direction of the H
electrons, sending them traveling along the north edge
of the bench toward the northeast [NE] corner.
Similarly, a mirror at a 45°-angle at the SE corner
changes the direction of the S electrons, sending them
traveling along the eastern edge of the bench toward
the NE corner. Thus far, the apparatus is made with a
hardness box plus two mirrors; it also includes a
collection box…
Located at the NE corner of the bench is a collection
box that collects and recombines the two streams of
electrons -- it recombines the electrons that traveled
north and then east with those electrons that traveled
east and then north. The collection box then shoots the
stream of recombined electron away from the bench to
the NE.
Let 'path h' refer to the path that H electrons take
from the SW hardness box north to the NW mirror and
then east to the collection box. Let 'path s' refer to
the path that S electrons take from the SW hardness box
east to the SE mirror and then north to the collection
box.
B.
Preliminary testing. Plenty of H electrons are fed into
the hardness box; and they all take path h and emerge
from the collection box and are verified to still be H
after their journey. A quantity of S electrons are fed
into the hardness box; they all take path s and emerge
from the collection box and are verified to remain S
electrons after their journey.
C.
Experiment #6: feed all W electrons into the SW
hardness box and detect for H/S in the collection box.
As expected, half the W electrons follow path h, and
half the W electrons follow path s. In the end, half
5 See David Z. Albert, Quantum Mechanics and Experience, Ch. 1.
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the electrons in the collection box are H and half are
S. No surprise here.
D.
Experiment #7: feed all H electrons into the SW
hardness box and detect for B/W in the collection box.
As expected, the H electrons all follow path h; no
electrons will have followed path s. In the collection
box at the end of path h, these electrons are detected
to have remained H; and half of these H electrons are B
and half of these H electrons are W. Again, no
surprises here. Note: the same outcome occurs if one
feeds all S electrons into the SW hardness box: after
they all follow path s (and none follows path h), they
remain soft in the collection box, and 50% are B and
50% are W.
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E.
Experiment #8: feed all W electrons into the SW
hardness box and detect for color at the end.
1.
2.
What results should you expect? The reasonable
expectation is developed in three steps:
a.
Having used a heretofore unmentioned color
box to generate a stream of W electrons, one
passes that stream of W electrons through the
SW hardness box. Half of those W electrons
are H and half are S; so, half the W
electrons will follow path h to the
collection box and the other half will follow
path s to the collection box. In the
collection box, then, half the collected
electrons will be detected to be H and half
will be detected to be S. This is not
problematic.
b.
Reminder: In the earlier three-box Experiment
#5, we learned that a stream of single-color
electrons passing through a hardness box will
produce H and S electrons that are
subsequently detected to be half W and half
B, suggesting that the mere detection of
hardness can alter the color of electrons.
c.
The bottom line regarding what one should
expect from the two-mirror apparatus: if a
stream of W electrons is sorted into half H
and half S electrons, then given the threebox experiment, one expects that those H and
S electrons will be subsequently measured to
be half W and half B -- that passing through
the hardness box will have causally altered
the color of half the incoming W electrons.
(There is no reason to believe that the
outcome will be any different from the threebox experiment: only W electrons are streamed
into the hardness box; half of all W
electrons are H; the other half are S; the H
and S electrons bounce off mirrors and land
in an inert holding container. So, given the
three-box experiment, you should expect that,
in the collection box, half the combined H/S
electrons will be W and half will be B.
The actual results. After passing a stream of W
electrons through the hardness box and collecting
them in the collection box, half are H and half
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are S. When those combined H and S electrons are
then tested for color (using, presumably, a color
box #2), one discovers that all collected
electrons are W! This outcome conflicts with the
outcome of the three-box experiment described
earlier! Now it appears that detecting hardness
does not affect the color of the incoming W
electrons!
F.
Experiment #9: repeat Experiment #8 with a barrier that
can be moved in to block path s and moved out to open
path s. When the barrier is moved out, the apparatus
operates exactly like Experiment #5.
1.
2.
What results should you expect if you stream all W
electrons into the hardness box and move the
barrier inward to block path s?
a.
If you stream all W electrons into the
hardness box, half are hard and half are
soft; so half will follow path h and half
will follow path s. So, if you block path s,
the total number of electrons that land in
the collection box will be decreased by 50%.
b.
Reminder: With no barrier (as in
Experiment #8), all electrons in the
collection box are detected to be white.
Thus, without the barrier, all the incoming W
electrons that take path h are white, and all
the incoming electrons that take path s are
white.
c.
The bottom line of what one should expect
with the barrier moved inward. Whether the
barrier is or isn't blocking path s should
have no affect on the color of electrons that
follow path h. So, if all the electrons on
path h are white without the barrier, there
is thereby every reason to conclude that all
the electrons along path h will be white with
the barrier moved inward. And these path-h
electrons are the only electrons that will
reach the collection box. So, there is every
reason to believe that only half the incoming
W electrons will reach the collection box and
that they will all be white.
The actual results. As predicted, with the barrier
in place, only half the incoming W electrons ever
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reach the collection box (and they reach it, of
course, via path h). The surprising result,
however, is that the electrons collected are not
all W! Half are W and half are B! How can this be?
(Take another moment to scratch your head and to
exhibit an appropriate expression of disbelief.)
This outcome conflicts with the outcome of
Experiment #8: Whether a barrier does or doesn't
block the path of S electrons should have nothing
to do with the color of a separate flow of H
electrons! But, apparently, there is a mysterious
connection after all.
3.
G.
Note: The same results occur if one blocks path h
instead of path s.
What should we claim about white electron E that is
inserted into the hardness box and lands in the
collection box in Experiment #8? Did E reach the
collection box via path h? Path s? Both? Neither?
1.
Reminder: If X = Y, then X and Y have all
properties in common.
2.
"E took path h to the collection box." Every
electron in the collection box, including E, has
the property of being definitively W. But
Experiment #9 suggests that any electron that
takes path h lacks the property of being
definitively W. So, E cannot be identical with any
electron that takes path h.
3.
"E took path s to the collection box." This fails
for the same reason: every electron in the
collection box, including E, has the property of
being definitively W. But Experiment #8 suggests
that any electron that takes path s (when path h
is blocked) lacks the property of being
definitively W. So, E cannot be identical with any
electron that takes path s.
4.
"E took both path h and path s to the collection
box." First, some would argue that it is
metaphysically impossible that a single entity
could wholly occupy two distinct places at the
same time. Second, after an electron is inserted
into the apparatus, it is always found on path h
or path s, but never both; and, no half-electrons
are ever found.
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V.
5.
"E took neither path h nor path s to the
collection box." This is not a viable option: if
one blocks both h and s, E would never have
reached the collection box. So, unless one
believes in mystical teletransportation, E cannot
jump from the hardness box to the collection box
without taking one path or the other.
6.
"Between entering the hardness box and entering
the collection box, E was in superposition:"
Between entering the hardness box at time t and
landing in the collection box at time t*, electron
E was something that exhibited a mysterious mode
of being that did not involve E's having a
particular set of intrinsic properties at a
particular time and location. (It is false that E
travels path h with the property being W; it is
false that E travels path h with the property
being non-W.)
Causation and spatiotemporal locality & quantum weirdness
If event E1 that occurs at time t1 is the (indirect)
sufficient causal condition of event E2 that occurs at later time
t5, then we assume that E1 has causal effects at every time
between t1 and t5. In short, we assume that an event at one time
cannot be causally connected with an event at a later time if
there is a time between these two events at which the first event
has no causal effect at all. If Socrates drinks hemlock at time t
and if Socrates dies at t5 and if the arsenic exhibits no causal
effect whatsoever at times t2, t3, and t4, then the hemlock
cannot have been the cause of Socrates’ death at t5. The temporal
gap would assure us that the two events are causally independent.
Similarly, if event E1 that occurs in spatial region S1 is
the (indirect) sufficient causal condition of event E2 that
occurs in spatial region S5, then we assume that E1 and E2 are
spatially local: E1 exhibits some causal effect within every
spatial region between S1 and S5. If the cue ball and eight ball
are a foot apart on the pool table and if the eight ball begins
rolling into a side pocket after you simply touch the top of the
cue ball with your finger, your touching the cue ball cannot be
the cause of the eight ball’s rolling: your touching the cue ball
had no causal effect on any of the spatial regions between the
two balls. The spatial gap assures us that the two events are
causally independent.
A potential problem. “But what about gravity? The Moon’s
gravity has an affect on the Earth’s oceans and a powerful magnet
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can causally effect a nail place several centimeters away. These
examples demonstrate the causation need not require spatial
locality -- there is such a thing as causation at a distance.”
This objection is right on target… unless we agree that (a) there
exists something (e.g. a gravitational field) that lies between
the Moon and Earth's oceans and (b) there exists something (e.g.
a magnetic field) that lies between the magnet and nail. If there
does exist a gravitational field between the Moon and oceans,
then the Moon is the indirect cause of the oceans' tidal changes:
the Moon, via its gravitational field, does exhibit causal
effects on every spatial region between the region occupied by
the Moon and the region occupied by the oceans.
Intrinsic properties. Presumably if an event that involves a
certain object at one place and time brings about an event
involving some other object at another place and time, then the
causal connection is a function of the intrinsic properties had
by each of the objects. If the lighting of a cigar causes a
forest fire, the causal connection is a function of certain
intrinsic (chemical, physical) properties had by the cigar and
other intrinsic properties had by the forest’s trees.
The weirdness. We want to say that the electron’s
approaching the double-slit wall is an (indirect) cause of its
striking a particular location on the detector. That is, various
facts about the electron as it approaches the wall -- facts that
may involve its mass, spin, charge, speed, trajectory, etc. -indirectly determine that it strikes the detector at a particular
place. If this is true, then the approaching electron must exert
(directly or indirectly) some causal effect involving every
region of space that it occupies between its approaching the wall
and its striking the wall. If, however, the electron lacks any
definitive location and lacks any definitive set of intrinsic
properties at any time between its approaching the double-slit
wall and its striking the detector, then it would seem that the
causal connection between the approaching electron and its
striking the wall violates the principle of spatial locality -that this causal connection involves a causal connection that
weirdly “travels across” a spatial gap and temporal gap. How can
this be?
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