Uncertainty principle for a sitting person
$begingroup$
If a person is sitting on a chair his momentum is zero and his uncertainty in position should be infinite. But we can obviously position him at most within few chair lengths.
What am I missing? Do we have to invoke earth's motion, motion of the galaxy etc. to resolve the issue?
heisenberg-uncertainty-principle estimation
edited Nov 14 '18 at 0:45
Qmechanic♦
105k121881202
asked Nov 12 '18 at 1:05
FakrudeenFakrudeen
349311
$endgroup$
|
show 5 more comments
$begingroup$
If a person is sitting on a chair his momentum is zero and his uncertainty in position should be infinite. But we can obviously position him at most within few chair lengths.
What am I missing? Do we have to invoke earth's motion, motion of the galaxy etc. to resolve the issue?
heisenberg-uncertainty-principle estimation
edited Nov 14 '18 at 0:45
Qmechanic♦
105k121881202
asked Nov 12 '18 at 1:05
FakrudeenFakrudeen
349311
$endgroup$
7
$begingroup$
I wonder if the quantum phenomena can still be observed in such a large scale system...
$endgroup$
– K_inverse
Nov 12 '18 at 1:16
2
$begingroup$
@K_inverse Yes, they can. But as soon as you try that, you'd realize neither the momentum nor the position is perfectly localized, so the premise of the question is false - you decidedly don't have "zero momentum" when sitting on a chair.
$endgroup$
– Luaan
Nov 12 '18 at 11:22
2
$begingroup$
If it is a rocking chair you don't have zero uncertainty in the position even at macroscopic level :-)
$endgroup$
– Francesco
Nov 12 '18 at 11:48
7
$begingroup$
You're confusing the momentum with the uncertainty in momentum.
$endgroup$
– mkrieger1
Nov 12 '18 at 13:54
18
$begingroup$
Since I unexpectedly gained huge momentum very unexpectedly while sitting on an IKEA chair, I have never again felt any certainty about my position in the universe.
$endgroup$
– Pavel
Nov 12 '18 at 19:44
|
show 5 more comments
$begingroup$
If a person is sitting on a chair his momentum is zero and his uncertainty in position should be infinite. But we can obviously position him at most within few chair lengths.
What am I missing? Do we have to invoke earth's motion, motion of the galaxy etc. to resolve the issue?
heisenberg-uncertainty-principle estimation
edited Nov 14 '18 at 0:45
Qmechanic♦
105k121881202
asked Nov 12 '18 at 1:05
FakrudeenFakrudeen
349311
$endgroup$
If a person is sitting on a chair his momentum is zero and his uncertainty in position should be infinite. But we can obviously position him at most within few chair lengths.
What am I missing? Do we have to invoke earth's motion, motion of the galaxy etc. to resolve the issue?
heisenberg-uncertainty-principle estimation
heisenberg-uncertainty-principle estimation
edited Nov 14 '18 at 0:45
Qmechanic♦
105k121881202
asked Nov 12 '18 at 1:05
FakrudeenFakrudeen
349311
edited Nov 14 '18 at 0:45
Qmechanic♦
105k121881202
asked Nov 12 '18 at 1:05
FakrudeenFakrudeen
349311
edited Nov 14 '18 at 0:45
Qmechanic♦
105k121881202
edited Nov 14 '18 at 0:45
Qmechanic♦
105k121881202
edited Nov 14 '18 at 0:45
Qmechanic♦
105k121881202
105k121881202
asked Nov 12 '18 at 1:05
FakrudeenFakrudeen
349311
asked Nov 12 '18 at 1:05
FakrudeenFakrudeen
349311
asked Nov 12 '18 at 1:05
FakrudeenFakrudeen
349311
349311
7
$begingroup$
I wonder if the quantum phenomena can still be observed in such a large scale system...
$endgroup$
– K_inverse
Nov 12 '18 at 1:16
2
$begingroup$
@K_inverse Yes, they can. But as soon as you try that, you'd realize neither the momentum nor the position is perfectly localized, so the premise of the question is false - you decidedly don't have "zero momentum" when sitting on a chair.
$endgroup$
– Luaan
Nov 12 '18 at 11:22
2
$begingroup$
If it is a rocking chair you don't have zero uncertainty in the position even at macroscopic level :-)
$endgroup$
– Francesco
Nov 12 '18 at 11:48
7
$begingroup$
You're confusing the momentum with the uncertainty in momentum.
$endgroup$
– mkrieger1
Nov 12 '18 at 13:54
18
$begingroup$
Since I unexpectedly gained huge momentum very unexpectedly while sitting on an IKEA chair, I have never again felt any certainty about my position in the universe.
$endgroup$
– Pavel
Nov 12 '18 at 19:44
|
show 5 more comments
7
$begingroup$
I wonder if the quantum phenomena can still be observed in such a large scale system...
$endgroup$
– K_inverse
Nov 12 '18 at 1:16
2
$begingroup$
@K_inverse Yes, they can. But as soon as you try that, you'd realize neither the momentum nor the position is perfectly localized, so the premise of the question is false - you decidedly don't have "zero momentum" when sitting on a chair.
$endgroup$
– Luaan
Nov 12 '18 at 11:22
2
$begingroup$
If it is a rocking chair you don't have zero uncertainty in the position even at macroscopic level :-)
$endgroup$
– Francesco
Nov 12 '18 at 11:48
7
$begingroup$
You're confusing the momentum with the uncertainty in momentum.
$endgroup$
– mkrieger1
Nov 12 '18 at 13:54
18
$begingroup$
Since I unexpectedly gained huge momentum very unexpectedly while sitting on an IKEA chair, I have never again felt any certainty about my position in the universe.
$endgroup$
– Pavel
Nov 12 '18 at 19:44
7
7
$begingroup$
I wonder if the quantum phenomena can still be observed in such a large scale system...
$endgroup$
– K_inverse
Nov 12 '18 at 1:16
$begingroup$
I wonder if the quantum phenomena can still be observed in such a large scale system...
$endgroup$
– K_inverse
Nov 12 '18 at 1:16
2
2
$begingroup$
@K_inverse Yes, they can. But as soon as you try that, you'd realize neither the momentum nor the position is perfectly localized, so the premise of the question is false - you decidedly don't have "zero momentum" when sitting on a chair.
$endgroup$
– Luaan
Nov 12 '18 at 11:22
$begingroup$
@K_inverse Yes, they can. But as soon as you try that, you'd realize neither the momentum nor the position is perfectly localized, so the premise of the question is false - you decidedly don't have "zero momentum" when sitting on a chair.
$endgroup$
– Luaan
Nov 12 '18 at 11:22
2
2
$begingroup$
If it is a rocking chair you don't have zero uncertainty in the position even at macroscopic level :-)
$endgroup$
– Francesco
Nov 12 '18 at 11:48
$begingroup$
If it is a rocking chair you don't have zero uncertainty in the position even at macroscopic level :-)
$endgroup$
– Francesco
Nov 12 '18 at 11:48
7
7
$begingroup$
You're confusing the momentum with the uncertainty in momentum.
$endgroup$
– mkrieger1
Nov 12 '18 at 13:54
$begingroup$
You're confusing the momentum with the uncertainty in momentum.
$endgroup$
– mkrieger1
Nov 12 '18 at 13:54
18
18
$begingroup$
Since I unexpectedly gained huge momentum very unexpectedly while sitting on an IKEA chair, I have never again felt any certainty about my position in the universe.
$endgroup$
– Pavel
Nov 12 '18 at 19:44
$begingroup$
Since I unexpectedly gained huge momentum very unexpectedly while sitting on an IKEA chair, I have never again felt any certainty about my position in the universe.
$endgroup$
– Pavel
Nov 12 '18 at 19:44
|
show 5 more comments
2 Answers
2
active
oldest
votes
$begingroup$
If a person is sitting on a chair his momentum is zero...
How close to zero?
The uncertainty principle says that if $Delta x$ is the uncertainty in position and $Delta p$ is the uncertainty in momentum, then $Delta x,Delta psim hbar$. So, consider an object with the mass of a person, say $M = 70$ kg. Suppose the uncertainty in this object's position is roughly the size of a proton, say $Delta x = 10^-15$ meters. The uncertainty principle says that the uncertainty in momentum must be
$$
Delta psimfrachbarDelta xapproxfrac1 times 10^-34text meter^2text kg / second10^-15text meterapprox 1times 10^-19text meter kg / second,
$$
so the uncertainty in the object's velocity is
$$
Delta v=fracDelta pMapprox fracapprox 1times 10^-19text meter kg / secondtext70 kgsim 1times 10^-21text meter / second.
$$
In other words, the uncertainty in the person's velocity would be roughly one proton-radius per month.
This shows that the uncertainties in a person's position and momentum can both be zero as far as we can ever hope to tell, and this is not at all in conflict with the uncertainty principle.
answered Nov 12 '18 at 1:22
Dan YandDan Yand
11.1k21540
$endgroup$
1
$begingroup$
Reminds me that science is closing in on producing quantum effects on the macro scale. We're a ways off from a human, but a 120 carbon atom bucky ball? Smashed. (A coherent beam of humans would be an interesting engineering challenge...)
$endgroup$
– Draco18s
Nov 12 '18 at 15:09
2
$begingroup$
@Draco18s Isn't that a marching column?
$endgroup$
– Pilchard123
Nov 12 '18 at 15:57
3
$begingroup$
@Pilchard123 Yeah, but they don't maintain their momentum uncertainties when walking through double doors.
$endgroup$
– Draco18s
Nov 12 '18 at 16:20
3
$begingroup$
+1 Great job taking a joke/troll question, applying correct physics, and ending with "zero as far as we can ever hope to tell".
$endgroup$
– AnoE
Nov 12 '18 at 23:03
9
$begingroup$
@AnoE - I wouldn't say that's a joke/troll question. It's interest to grasp the basics of uncertainty principle. In fact, basic physics textbooks examples are not far away from that question.
$endgroup$
– Pere
Nov 13 '18 at 10:33
|
show 3 more comments
$begingroup$
If we pretend that person is a quantum mechanical particle of mass $m=75$ kg and we localize him in a box of length $L=1$ m, then the resulting uncertainty in his velocity would be about one Planck length per second. Are you sure you know his velocity to within one Planck length per second?
Applying quantum mechanical principles to classical systems is always a recipe for disaster, but this underlying point is a good one - in macroscopic systems, the uncertainty principle implies fundamental uncertainties which are so small as to be completely meaningless from an observational point of view. If you were moving at a planck length per second for a hundred quadrillion years, you'd be about halfway across a hydrogen atom.
answered Nov 12 '18 at 1:19
J. MurrayJ. Murray
7,7852723
$endgroup$
19
$begingroup$
I tried doing the experiment you suggest in your last sentence but the damned hydrogen atom wouldn't sit still and I gave up after a couple of weeks.
$endgroup$
– David Richerby
Nov 12 '18 at 17:50
7
$begingroup$
@DavidRicherby I'd be more concerned if you had convinced a hydrogen atom to stay still
$endgroup$
– SGR
Nov 13 '18 at 13:34
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
If a person is sitting on a chair his momentum is zero...
How close to zero?
The uncertainty principle says that if $Delta x$ is the uncertainty in position and $Delta p$ is the uncertainty in momentum, then $Delta x,Delta psim hbar$. So, consider an object with the mass of a person, say $M = 70$ kg. Suppose the uncertainty in this object's position is roughly the size of a proton, say $Delta x = 10^-15$ meters. The uncertainty principle says that the uncertainty in momentum must be
$$
Delta psimfrachbarDelta xapproxfrac1 times 10^-34text meter^2text kg / second10^-15text meterapprox 1times 10^-19text meter kg / second,
$$
so the uncertainty in the object's velocity is
$$
Delta v=fracDelta pMapprox fracapprox 1times 10^-19text meter kg / secondtext70 kgsim 1times 10^-21text meter / second.
$$
In other words, the uncertainty in the person's velocity would be roughly one proton-radius per month.
This shows that the uncertainties in a person's position and momentum can both be zero as far as we can ever hope to tell, and this is not at all in conflict with the uncertainty principle.
answered Nov 12 '18 at 1:22
Dan YandDan Yand
11.1k21540
$endgroup$
1
$begingroup$
Reminds me that science is closing in on producing quantum effects on the macro scale. We're a ways off from a human, but a 120 carbon atom bucky ball? Smashed. (A coherent beam of humans would be an interesting engineering challenge...)
$endgroup$
– Draco18s
Nov 12 '18 at 15:09
2
$begingroup$
@Draco18s Isn't that a marching column?
$endgroup$
– Pilchard123
Nov 12 '18 at 15:57
3
$begingroup$
@Pilchard123 Yeah, but they don't maintain their momentum uncertainties when walking through double doors.
$endgroup$
– Draco18s
Nov 12 '18 at 16:20
3
$begingroup$
+1 Great job taking a joke/troll question, applying correct physics, and ending with "zero as far as we can ever hope to tell".
$endgroup$
– AnoE
Nov 12 '18 at 23:03
9
$begingroup$
@AnoE - I wouldn't say that's a joke/troll question. It's interest to grasp the basics of uncertainty principle. In fact, basic physics textbooks examples are not far away from that question.
$endgroup$
– Pere
Nov 13 '18 at 10:33
|
show 3 more comments
$begingroup$
If a person is sitting on a chair his momentum is zero...
How close to zero?
The uncertainty principle says that if $Delta x$ is the uncertainty in position and $Delta p$ is the uncertainty in momentum, then $Delta x,Delta psim hbar$. So, consider an object with the mass of a person, say $M = 70$ kg. Suppose the uncertainty in this object's position is roughly the size of a proton, say $Delta x = 10^-15$ meters. The uncertainty principle says that the uncertainty in momentum must be
$$
Delta psimfrachbarDelta xapproxfrac1 times 10^-34text meter^2text kg / second10^-15text meterapprox 1times 10^-19text meter kg / second,
$$
so the uncertainty in the object's velocity is
$$
Delta v=fracDelta pMapprox fracapprox 1times 10^-19text meter kg / secondtext70 kgsim 1times 10^-21text meter / second.
$$
In other words, the uncertainty in the person's velocity would be roughly one proton-radius per month.
This shows that the uncertainties in a person's position and momentum can both be zero as far as we can ever hope to tell, and this is not at all in conflict with the uncertainty principle.
answered Nov 12 '18 at 1:22
Dan YandDan Yand
11.1k21540
$endgroup$
1
$begingroup$
Reminds me that science is closing in on producing quantum effects on the macro scale. We're a ways off from a human, but a 120 carbon atom bucky ball? Smashed. (A coherent beam of humans would be an interesting engineering challenge...)
$endgroup$
– Draco18s
Nov 12 '18 at 15:09
2
$begingroup$
@Draco18s Isn't that a marching column?
$endgroup$
– Pilchard123
Nov 12 '18 at 15:57
3
$begingroup$
@Pilchard123 Yeah, but they don't maintain their momentum uncertainties when walking through double doors.
$endgroup$
– Draco18s
Nov 12 '18 at 16:20
3
$begingroup$
+1 Great job taking a joke/troll question, applying correct physics, and ending with "zero as far as we can ever hope to tell".
$endgroup$
– AnoE
Nov 12 '18 at 23:03
9
$begingroup$
@AnoE - I wouldn't say that's a joke/troll question. It's interest to grasp the basics of uncertainty principle. In fact, basic physics textbooks examples are not far away from that question.
$endgroup$
– Pere
Nov 13 '18 at 10:33
|
show 3 more comments
$begingroup$
If a person is sitting on a chair his momentum is zero...
How close to zero?
The uncertainty principle says that if $Delta x$ is the uncertainty in position and $Delta p$ is the uncertainty in momentum, then $Delta x,Delta psim hbar$. So, consider an object with the mass of a person, say $M = 70$ kg. Suppose the uncertainty in this object's position is roughly the size of a proton, say $Delta x = 10^-15$ meters. The uncertainty principle says that the uncertainty in momentum must be
$$
Delta psimfrachbarDelta xapproxfrac1 times 10^-34text meter^2text kg / second10^-15text meterapprox 1times 10^-19text meter kg / second,
$$
so the uncertainty in the object's velocity is
$$
Delta v=fracDelta pMapprox fracapprox 1times 10^-19text meter kg / secondtext70 kgsim 1times 10^-21text meter / second.
$$
In other words, the uncertainty in the person's velocity would be roughly one proton-radius per month.
This shows that the uncertainties in a person's position and momentum can both be zero as far as we can ever hope to tell, and this is not at all in conflict with the uncertainty principle.
answered Nov 12 '18 at 1:22
Dan YandDan Yand
11.1k21540
$endgroup$
If a person is sitting on a chair his momentum is zero...
How close to zero?
The uncertainty principle says that if $Delta x$ is the uncertainty in position and $Delta p$ is the uncertainty in momentum, then $Delta x,Delta psim hbar$. So, consider an object with the mass of a person, say $M = 70$ kg. Suppose the uncertainty in this object's position is roughly the size of a proton, say $Delta x = 10^-15$ meters. The uncertainty principle says that the uncertainty in momentum must be
$$
Delta psimfrachbarDelta xapproxfrac1 times 10^-34text meter^2text kg / second10^-15text meterapprox 1times 10^-19text meter kg / second,
$$
so the uncertainty in the object's velocity is
$$
Delta v=fracDelta pMapprox fracapprox 1times 10^-19text meter kg / secondtext70 kgsim 1times 10^-21text meter / second.
$$
In other words, the uncertainty in the person's velocity would be roughly one proton-radius per month.
This shows that the uncertainties in a person's position and momentum can both be zero as far as we can ever hope to tell, and this is not at all in conflict with the uncertainty principle.
answered Nov 12 '18 at 1:22
Dan YandDan Yand
11.1k21540
edited Nov 12 '18 at 1:42
answered Nov 12 '18 at 1:22
Dan YandDan Yand
11.1k21540
answered Nov 12 '18 at 1:22
Dan YandDan Yand
11.1k21540
answered Nov 12 '18 at 1:22
Dan YandDan Yand
11.1k21540
11.1k21540
1
$begingroup$
Reminds me that science is closing in on producing quantum effects on the macro scale. We're a ways off from a human, but a 120 carbon atom bucky ball? Smashed. (A coherent beam of humans would be an interesting engineering challenge...)
$endgroup$
– Draco18s
Nov 12 '18 at 15:09
2
$begingroup$
@Draco18s Isn't that a marching column?
$endgroup$
– Pilchard123
Nov 12 '18 at 15:57
3
$begingroup$
@Pilchard123 Yeah, but they don't maintain their momentum uncertainties when walking through double doors.
$endgroup$
– Draco18s
Nov 12 '18 at 16:20
3
$begingroup$
+1 Great job taking a joke/troll question, applying correct physics, and ending with "zero as far as we can ever hope to tell".
$endgroup$
– AnoE
Nov 12 '18 at 23:03
9
$begingroup$
@AnoE - I wouldn't say that's a joke/troll question. It's interest to grasp the basics of uncertainty principle. In fact, basic physics textbooks examples are not far away from that question.
$endgroup$
– Pere
Nov 13 '18 at 10:33
|
show 3 more comments
1
$begingroup$
Reminds me that science is closing in on producing quantum effects on the macro scale. We're a ways off from a human, but a 120 carbon atom bucky ball? Smashed. (A coherent beam of humans would be an interesting engineering challenge...)
$endgroup$
– Draco18s
Nov 12 '18 at 15:09
2
$begingroup$
@Draco18s Isn't that a marching column?
$endgroup$
– Pilchard123
Nov 12 '18 at 15:57
3
$begingroup$
@Pilchard123 Yeah, but they don't maintain their momentum uncertainties when walking through double doors.
$endgroup$
– Draco18s
Nov 12 '18 at 16:20
3
$begingroup$
+1 Great job taking a joke/troll question, applying correct physics, and ending with "zero as far as we can ever hope to tell".
$endgroup$
– AnoE
Nov 12 '18 at 23:03
9
$begingroup$
@AnoE - I wouldn't say that's a joke/troll question. It's interest to grasp the basics of uncertainty principle. In fact, basic physics textbooks examples are not far away from that question.
$endgroup$
– Pere
Nov 13 '18 at 10:33
1
1
$begingroup$
Reminds me that science is closing in on producing quantum effects on the macro scale. We're a ways off from a human, but a 120 carbon atom bucky ball? Smashed. (A coherent beam of humans would be an interesting engineering challenge...)
$endgroup$
– Draco18s
Nov 12 '18 at 15:09
$begingroup$
Reminds me that science is closing in on producing quantum effects on the macro scale. We're a ways off from a human, but a 120 carbon atom bucky ball? Smashed. (A coherent beam of humans would be an interesting engineering challenge...)
$endgroup$
– Draco18s
Nov 12 '18 at 15:09
2
2
$begingroup$
@Draco18s Isn't that a marching column?
$endgroup$
– Pilchard123
Nov 12 '18 at 15:57
$begingroup$
@Draco18s Isn't that a marching column?
$endgroup$
– Pilchard123
Nov 12 '18 at 15:57
3
3
$begingroup$
@Pilchard123 Yeah, but they don't maintain their momentum uncertainties when walking through double doors.
$endgroup$
– Draco18s
Nov 12 '18 at 16:20
$begingroup$
@Pilchard123 Yeah, but they don't maintain their momentum uncertainties when walking through double doors.
$endgroup$
– Draco18s
Nov 12 '18 at 16:20
3
3
$begingroup$
+1 Great job taking a joke/troll question, applying correct physics, and ending with "zero as far as we can ever hope to tell".
$endgroup$
– AnoE
Nov 12 '18 at 23:03
$begingroup$
+1 Great job taking a joke/troll question, applying correct physics, and ending with "zero as far as we can ever hope to tell".
$endgroup$
– AnoE
Nov 12 '18 at 23:03
9
9
$begingroup$
@AnoE - I wouldn't say that's a joke/troll question. It's interest to grasp the basics of uncertainty principle. In fact, basic physics textbooks examples are not far away from that question.
$endgroup$
– Pere
Nov 13 '18 at 10:33
$begingroup$
@AnoE - I wouldn't say that's a joke/troll question. It's interest to grasp the basics of uncertainty principle. In fact, basic physics textbooks examples are not far away from that question.
$endgroup$
– Pere
Nov 13 '18 at 10:33
|
show 3 more comments
$begingroup$
If we pretend that person is a quantum mechanical particle of mass $m=75$ kg and we localize him in a box of length $L=1$ m, then the resulting uncertainty in his velocity would be about one Planck length per second. Are you sure you know his velocity to within one Planck length per second?
Applying quantum mechanical principles to classical systems is always a recipe for disaster, but this underlying point is a good one - in macroscopic systems, the uncertainty principle implies fundamental uncertainties which are so small as to be completely meaningless from an observational point of view. If you were moving at a planck length per second for a hundred quadrillion years, you'd be about halfway across a hydrogen atom.
answered Nov 12 '18 at 1:19
J. MurrayJ. Murray
7,7852723
$endgroup$
19
$begingroup$
I tried doing the experiment you suggest in your last sentence but the damned hydrogen atom wouldn't sit still and I gave up after a couple of weeks.
$endgroup$
– David Richerby
Nov 12 '18 at 17:50
7
$begingroup$
@DavidRicherby I'd be more concerned if you had convinced a hydrogen atom to stay still
$endgroup$
– SGR
Nov 13 '18 at 13:34
add a comment |
$begingroup$
If we pretend that person is a quantum mechanical particle of mass $m=75$ kg and we localize him in a box of length $L=1$ m, then the resulting uncertainty in his velocity would be about one Planck length per second. Are you sure you know his velocity to within one Planck length per second?
Applying quantum mechanical principles to classical systems is always a recipe for disaster, but this underlying point is a good one - in macroscopic systems, the uncertainty principle implies fundamental uncertainties which are so small as to be completely meaningless from an observational point of view. If you were moving at a planck length per second for a hundred quadrillion years, you'd be about halfway across a hydrogen atom.
answered Nov 12 '18 at 1:19
J. MurrayJ. Murray
7,7852723
$endgroup$
19
$begingroup$
I tried doing the experiment you suggest in your last sentence but the damned hydrogen atom wouldn't sit still and I gave up after a couple of weeks.
$endgroup$
– David Richerby
Nov 12 '18 at 17:50
7
$begingroup$
@DavidRicherby I'd be more concerned if you had convinced a hydrogen atom to stay still
$endgroup$
– SGR
Nov 13 '18 at 13:34
add a comment |
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If we pretend that person is a quantum mechanical particle of mass $m=75$ kg and we localize him in a box of length $L=1$ m, then the resulting uncertainty in his velocity would be about one Planck length per second. Are you sure you know his velocity to within one Planck length per second?
Applying quantum mechanical principles to classical systems is always a recipe for disaster, but this underlying point is a good one - in macroscopic systems, the uncertainty principle implies fundamental uncertainties which are so small as to be completely meaningless from an observational point of view. If you were moving at a planck length per second for a hundred quadrillion years, you'd be about halfway across a hydrogen atom.
answered Nov 12 '18 at 1:19
J. MurrayJ. Murray
7,7852723
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If we pretend that person is a quantum mechanical particle of mass $m=75$ kg and we localize him in a box of length $L=1$ m, then the resulting uncertainty in his velocity would be about one Planck length per second. Are you sure you know his velocity to within one Planck length per second?
Applying quantum mechanical principles to classical systems is always a recipe for disaster, but this underlying point is a good one - in macroscopic systems, the uncertainty principle implies fundamental uncertainties which are so small as to be completely meaningless from an observational point of view. If you were moving at a planck length per second for a hundred quadrillion years, you'd be about halfway across a hydrogen atom.
answered Nov 12 '18 at 1:19
J. MurrayJ. Murray
7,7852723
answered Nov 12 '18 at 1:19
J. MurrayJ. Murray
7,7852723
answered Nov 12 '18 at 1:19
J. MurrayJ. Murray
7,7852723
answered Nov 12 '18 at 1:19
J. MurrayJ. Murray
7,7852723
7,7852723
19
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I tried doing the experiment you suggest in your last sentence but the damned hydrogen atom wouldn't sit still and I gave up after a couple of weeks.
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– David Richerby
Nov 12 '18 at 17:50
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@DavidRicherby I'd be more concerned if you had convinced a hydrogen atom to stay still
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– SGR
Nov 13 '18 at 13:34
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19
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I tried doing the experiment you suggest in your last sentence but the damned hydrogen atom wouldn't sit still and I gave up after a couple of weeks.
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– David Richerby
Nov 12 '18 at 17:50
7
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@DavidRicherby I'd be more concerned if you had convinced a hydrogen atom to stay still
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– SGR
Nov 13 '18 at 13:34
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19
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I tried doing the experiment you suggest in your last sentence but the damned hydrogen atom wouldn't sit still and I gave up after a couple of weeks.
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– David Richerby
Nov 12 '18 at 17:50
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I tried doing the experiment you suggest in your last sentence but the damned hydrogen atom wouldn't sit still and I gave up after a couple of weeks.
$endgroup$
– David Richerby
Nov 12 '18 at 17:50
7
7
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@DavidRicherby I'd be more concerned if you had convinced a hydrogen atom to stay still
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– SGR
Nov 13 '18 at 13:34
$begingroup$
@DavidRicherby I'd be more concerned if you had convinced a hydrogen atom to stay still
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– SGR
Nov 13 '18 at 13:34
add a comment |
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7
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I wonder if the quantum phenomena can still be observed in such a large scale system...
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– K_inverse
Nov 12 '18 at 1:16
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@K_inverse Yes, they can. But as soon as you try that, you'd realize neither the momentum nor the position is perfectly localized, so the premise of the question is false - you decidedly don't have "zero momentum" when sitting on a chair.
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– Luaan
Nov 12 '18 at 11:22
2
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If it is a rocking chair you don't have zero uncertainty in the position even at macroscopic level :-)
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– Francesco
Nov 12 '18 at 11:48
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You're confusing the momentum with the uncertainty in momentum.
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– mkrieger1
Nov 12 '18 at 13:54
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Since I unexpectedly gained huge momentum very unexpectedly while sitting on an IKEA chair, I have never again felt any certainty about my position in the universe.
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– Pavel
Nov 12 '18 at 19:44