Schrödinger's Cat: A History of Quantum Physics [13:52]

--> YouTube-Generated Transcript <--
0:00 · you've probably heard of the thought
0:02 · experiment called Schroinger's cat and
0:04 · no it's it's not about an actual cat
0:06 · it's intended to illustrate an issue in
0:08 · quantum mechanics called the measurement
0:10 · problem in quantum mechanics events
0:12 · occur in a state of superp position
0:14 · literally at the quantum level multiple
0:16 · events can be occurring at the same time
0:18 · until they are finally observed in which
0:19 · case the superposition resolves itself
0:22 · into a single event it's a highly
0:24 · technical and heady problem that's
0:25 · rather elegantly explained with the
0:27 · thought experiment of Schroinger's cat
0:28 · but it may surprise you to find out that
0:30 · when Schroinger introduced the idea he
0:33 · was talking about something else
0:34 · entirely it is history that deserves to
0:37 · be remembered
0:39 · [Music]
0:42 · it might seem surprising to a modern
0:44 · audience but by 1900 the atomic theory
0:47 · of matter that is that all matter is
0:48 · made up of atoms was not fully explained
0:51 · or even universally accepted while the
0:53 · origins of the theory dated to the 18th
0:55 · or early 19th century the exact nature
0:57 · of atoms was still not understood
1:00 · austrian physicist Ernst Mock whose
1:02 · research on sound waves would lead to
1:04 · naming the speed of sound Mach
1:06 · proclaimed after an 1897 lecture that I
1:08 · don't believe atoms exist mock argued
1:11 · instead that atoms were just useful
1:12 · mental concepts for explaining
1:14 · observations but not real mock was just
1:17 · one of a number of scientists who argued
1:18 · against the atomic theory in the 19th
1:20 · century despite some resistance research
1:23 · on atoms continued to produce results
1:25 · right at the turn of the 20th century
1:27 · English physicist JJ Thompson's work on
1:30 · electrons showed that the atom was not
1:31 · the smallest form of matter at all and
1:33 · in 1904 he proposed the first atomic
1:35 · model with subatomic constituents his
1:38 · model the plum pudding model would soon
1:40 · prove incorrect but the discovery that
1:42 · atoms themselves were made up of even
1:44 · tinier pieces would be critical to the
1:46 · formation of an entirely new field of
1:49 · physics
1:50 · problems with classical physics have
1:52 · begun appearing in the 19th century when
1:53 · traditional physics began failing to
1:55 · explain certain phenomena there was for
1:58 · instance the Gibbs paradox in which the
2:00 · expression for entropy appears to
2:02 · violate the second law of thermodynamics
2:05 · other issues also cropped up such as
2:08 · with thermal radiation when an object is
2:10 · heated it becomes first red hot and if
2:12 · it is heated further will emit other
2:14 · colors first yellow white and then blue
2:16 · as it emits light at shorter wavelengths
2:19 · a perfect emitter like this would at
2:21 · cold temperatures appear perfectly black
2:23 · absorbing all light but emitting none
2:25 · this ideal emitter was called a black
2:27 · body and the radiation it emitted black
2:29 · body radiation and while they could
2:31 · explain experimental results at large
2:33 · wavelengths at short wavelengths the
2:35 · theories strongly disagreed with
2:36 · experimental results and in fact
2:39 · classical mechanics seem to predict that
2:40 · at very short wavelengths energy would
2:42 · be emitted at an infinite rate this is
2:45 · called the ultraviolet catastrophe
2:47 · physicists developed a second theory
2:49 · that explained the results at short
2:50 · wavelengths but which likewise failed to
2:52 · explain the results at longer
2:54 · wavelengths the issue was not trivial
2:56 · and scientists sought a single theory
2:58 · that explained all of the results
3:00 · max Planck was the first to explain all
3:03 · the results in 1900 with a new theory
3:05 · instead of imagining that energy could
3:07 · be admitted at any arbitrary amount he
3:09 · proposed harmonic oscillators that were
3:12 · in equilibrium with the thermal
3:13 · radiation each of these oscillators he
3:16 · said emitted energy only at a single
3:17 · characteristic frequency the energy
3:20 · emitted by any particular oscillator was
3:22 · therefore quantized this idea would
3:24 · become known as the plank relation and
3:26 · the constant in the equation as plank's
3:29 · constant
3:30 · this was the first quantum theory in
3:33 · physics and plank was awarded the Nobel
3:35 · Prize in physics in 1918 for the
3:38 · services rendered to the advancement of
3:40 · physics by his discovery of energy
3:42 · quanta it's difficult to overstate how
3:45 · this understanding would transform
3:46 · physics it was the foundation for the
3:49 · theories that would solve many of the
3:50 · issues in classical mechanics in 1905
3:53 · Albert Einstein applied the theory of
3:55 · quanta to a different issue in the late
3:58 · 1890s JJ Thompson had discovered
4:00 · electrons but in 1902 Hungarian
4:02 · physicist Philip Leonard was surprised
4:05 · that the energy of electrons ejected
4:06 · when light hits a metallic surface are
4:08 · not related to the intensity of the
4:10 · light as classical mechanics predicted
4:13 · einstein suggested that for
4:14 · instantaneous transitions of energy the
4:17 · energy in light might occur in a finite
4:19 · number of energy quanta in his 1905
4:23 · paper on a huristic viewpoint
4:24 · considering the emissions and
4:26 · transformation of light Einstein wrote
4:28 · that when a light ray is spreading from
4:29 · a point the energy is not distributed
4:31 · continuously over everinccreasing spaces
4:34 · but consist of a finite number of energy
4:36 · quanta that are localized in points in
4:38 · space move without dividing and can be
4:40 · absorbing or generating as a whole
4:43 · albert Fosling a German physicist turned
4:45 · scientific journalist called this
4:47 · sentence the most revolutionary sentence
4:50 · written by a physicist in the 20th
4:52 · century this work is what earned
4:54 · Einstein the Nobel Prize in physics in
4:56 · 1921
4:58 · the quantum theory of light was followed
5:00 · by the work of Danish theoretical
5:01 · physicist Neils Boore who used quantum
5:04 · theory to explain the emission spectrum
5:06 · of atoms when gas is heated it emits
5:09 · light at discrete frequencies bore
5:11 · proposed a new model of the atom which
5:13 · included quantized electron orbits this
5:16 · created essentially our modern
5:17 · understanding of the atom a dense
5:19 · nucleus surrounded by orbiting electrons
5:21 · that orbit at discrete orbits when the
5:23 · electrons move from one orbit to another
5:25 · they release photons at specific
5:27 · energies creating emission spectrums all
5:31 · these theories were really applied as
5:32 · corrections to classical mechanics but
5:35 · not as yet as their own field that
5:38 · changed as physicists continued to
5:39 · develop new explanations in 1924 French
5:42 · theoretical physicist Lewis de Bruy
5:45 · published the hypothesis that matter has
5:47 · wave properties an idea that was proven
5:49 · experimentally
5:51 · two theories quickly followed the
5:52 · development of matrix mechanics by
5:54 · German physicist Wner Heisenberg Max
5:56 · Bourne and Pascal Yordan and wave
5:59 · mechanics developed by Austrianborn
6:01 · theoretical physicist Irvin Schroinger
6:03 · schroinger showed that the two mechanics
6:05 · were in fact equivalent schroinger went
6:08 · on to apply the concepts to the hydrogen
6:10 · atom describing four properties of an
6:12 · atom put together they described the
6:14 · electrons quantum state multiple
6:16 · physicists such as Boore and Heisenberg
6:19 · attempted to explain the experimental
6:20 · results in what became known as the
6:22 · Copenhagen interpretation after Bo's
6:24 · institute in the Danish city where
6:26 · Heisenberg worked as an assistant no
6:28 · actual definitive version of the
6:30 · interpretation exists as the physicists
6:32 · held a variety of differing opinions
6:34 · there were some characteristic ideas
6:35 · however such as that a system is
6:37 · completely described by a quantum state
6:39 · and that atomic interactions are
6:41 · discontinuous others include the Bourne
6:44 · rule of max Bourne which says that the
6:46 · description of nature is essentially
6:48 · probabilistic and Heisenberg's
6:50 · uncertainty principle which states that
6:52 · we can't know both the position and
6:54 · speed of a particle with perfect
6:55 · accuracy simultaneously
6:58 · more complex is quantum superposition
7:00 · which posits that a quantum system can
7:02 · exist in multiple potential states until
7:04 · a measurement is made when the wave
7:07 · function collapses into one of those
7:08 · states the Copenhagen interpretation was
7:12 · far from universally agreed upon among
7:14 · the most notable critics was Albert
7:15 · Einstein himself einstein didn't have
7:18 · issues with the experimental results but
7:20 · doubted the conclusions of some others
7:22 · like Boore and thought that quantum
7:24 · mechanics remained an incomplete theory
7:26 · the disagreements are highly technical
7:28 · and have been repeatedly discussed among
7:30 · physicists much of it sprung from the
7:32 · idea that physicists like Boore and
7:33 · Heisenberg believed their theory was
7:35 · complete bourne and Heisenberg wrote in
7:37 · 1928 that the theory was a closed theory
7:40 · whose fundamental physical and
7:41 · mathematical assumptions are no longer
7:43 · susceptible to any modification
7:46 · einstein find that there were still
7:47 · significant unanswered or
7:49 · unsatisfactorily answered questions one
7:51 · of the primary disagreements regarded
7:53 · the implications about the construction
7:54 · of reality according to Heisenberg
7:57 · physical reality was only defined at the
7:59 · moment of observation another issue
8:01 · stemmed from Heisenberg's uncertainty
8:03 · principle in 1935 a paper was published
8:05 · under the authors Einstein Boris
8:08 · Bidolski and Nathan Rosen which
8:10 · challenged the idea that the theory was
8:11 · complete entitled can quantum mechanical
8:14 · description of physical reality be
8:16 · considered complete and now generally
8:18 · known as the EPR paper the paper
8:20 · attempts to construct a thought
8:21 · experiment paradox according to the
8:23 · rules of the Copenhagen interpretation
8:26 · this thought experiment imagined two
8:28 · particles A and B which interact briefly
8:30 · and then move off in opposite directions
8:32 · according to the uncertainty principle
8:34 · it's not possible to measure both the
8:36 · position and momentum of particle B
8:38 · precisely but you could measure the
8:40 · position of a particle A according to
8:42 · the paper finding the position of
8:44 · particle A meant that you could
8:45 · calculate the exact position of B and
8:48 · finding the momentum of A the momentum
8:49 · of B could be calculated the argument
8:52 · was essentially that absent a direct
8:53 · observation the momentum or the position
8:56 · of particle B could be measured meaning
8:58 · that there was a reality to those things
9:00 · independent of their observation
9:02 · this the paper argued meant that the
9:04 · wave function does not provide a
9:06 · complete description of the physical
9:07 · reality bore objected and argued later
9:10 · that year that the paper's reasoning was
9:11 · faulty for Einstein's part in letters to
9:14 · Irvin Schroinger he said that the paper
9:16 · did not really represent his views and
9:18 · that it was mostly written by Bolski he
9:20 · said that the reality of particle B's
9:22 · momentum or position is a sausage to me
9:25 · a German saying meaning that he couldn't
9:27 · care less instead he focused on the
9:29 · issue of non-locality it made no sense
9:32 · he thought that measuring particle A
9:34 · could lead to two states for particle B
9:37 · no matter how far apart they were
9:40 · quantum states as it stood he thought
9:42 · couldn't accurately reflect reality the
9:44 · same year the EPR paper was published
9:46 · Shreddinger wrote to Einstein to
9:48 · congratulate him for challenging the
9:49 · dogmatic quantum mechanics the
9:52 · correspondence which continued was in
9:54 · essence a series of critiques of Boore
9:55 · and his school in August Einstein asked
9:58 · Schroinger to imagine if the small-cale
10:00 · mechanics physicists talked about were
10:02 · enlarged suppose you had an unstable
10:04 · barrel of gunpowder that had an equal
10:06 · probability of exploding or not
10:08 · exploding in the next year after a year
10:10 · the mathematical equations in quantum
10:12 · mechanics would cease to make sense as
10:13 · they would describe a sort of blend of
10:16 · not yet and already exploded systems in
10:19 · reality Einstein said there is no such
10:21 · intermediary between exploded and not
10:23 · exploded troinger took that concept and
10:26 · imagined his own scenario which he
10:28 · called a quite ridiculous case confined
10:31 · in a steel chamber is a geer counter
10:33 · prepared with a tiny amount of uranium
10:35 · so small that in the next hour it's just
10:37 · as probable to expect one atomic decay
10:39 · as none an amplified relay provides that
10:41 · the first atomic decay shatters a small
10:43 · bottle of pressic acid this and cruy a
10:47 · cat is also trapped in the steel chamber
10:49 · after an hour he said "Quantum mechanics
10:51 · would say the living and dead cat are
10:53 · smeared out in equal measure." Einstein
10:56 · liked the thought experiment a wave
10:58 · function that contains a living as well
11:00 · as the dead cat just cannot be taken as
11:02 · a description of the real state of
11:03 · affairs einstein agreed writing to
11:05 · Schroinger that nobody really doubts
11:07 · that the presence or absence of the cat
11:09 · is something independent of the act of
11:11 · observation einstein also had some
11:13 · philosophical disagreements regarding
11:15 · the Copenhagen interpretation's idea
11:16 · that quantum physics was essentially
11:18 · probabilistic and not deterministic
11:20 · famously he wrote in 1926 that God does
11:22 · not play dice with the universe he
11:24 · qualified the statement in a 1945 letter
11:27 · writing that God tirelessly plays dice
11:29 · under laws which he himself has
11:30 · prescribed many have attempted in the
11:33 · years since his death to better
11:34 · understand his reservations and ideas
11:36 · about quantum mechanics schroinger
11:38 · published his famous cat thought
11:40 · experiment in November 1935 in the
11:42 · German magazine Natural Sciences he
11:44 · almost withdrew it when the Jewish
11:46 · editor of the magazine Arnold Berliner
11:48 · was fired due to policies of the Nazi
11:50 · government but decided to publish it
11:52 · anyway at Berlin's request the point was
11:55 · to highlight the incompleteness of the
11:57 · model to critique the Copenhagen
11:58 · interpretation but instead the thought
12:01 · experiment has become part of the
12:02 · foundation of quantum mechanics much
12:04 · discussed in theoretical discussions
12:07 · and to answer the obvious question no so
12:10 · far as we know Irvin Schroinger did not
12:13 · own a cat
12:15 · boore didn't respond directly to
12:17 · Schroinger's paper but the two continued
12:19 · to correspond and in the end the
12:21 · Copenhagen interpretation wasn't all
12:23 · that bothered by the observations of
12:24 · Einstein and Schroinger and actually the
12:27 · concept that the cat can exist in two
12:29 · states at the same time is now a
12:31 · fundamental part of quantum mechanics or
12:33 · at least at the quantum level scientists
12:35 · have continued to test quantum mechanics
12:37 · and the Copenhagen interpretation is
12:39 · still the leading explanation for
12:41 · quantum mechanics but the historical
12:43 · irony is that Schroinger's cat is often
12:46 · used to illustrate the counterintuitive
12:48 · elements of quantum mechanics today and
12:51 · the fact that he introduced the thought
12:53 · experiment not to explain quantum
12:55 · mechanics but to challenge it has
12:57 · largely been forgotten
13:00 · i hope you enjoyed watching this episode
13:02 · of the history guy and if you did please
13:03 · feel free to like and subscribe and
13:05 · share the history guy with your friends
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13:09 · deserves to be remembered then you can
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13:18 · also check out our great merchandise
13:20 · shop or book a special message from the
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13:30 · [Music]
13:39 · heat heat
13:42 · [Applause]
13:48 · [Applause]
13:49 · [Music]

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--> YouTube-Generated Transcript <--
0:00	·	you've probably heard of the thought
0:02	·	experiment called Schroinger's cat and
0:04	·	no it's it's not about an actual cat
0:06	·	it's intended to illustrate an issue in
0:08	·	quantum mechanics called the measurement
0:10	·	problem in quantum mechanics events
0:12	·	occur in a state of superp position
0:14	·	literally at the quantum level multiple
0:16	·	events can be occurring at the same time
0:18	·	until they are finally observed in which
0:19	·	case the superposition resolves itself
0:22	·	into a single event it's a highly
0:24	·	technical and heady problem that's
0:25	·	rather elegantly explained with the
0:27	·	thought experiment of Schroinger's cat
0:28	·	but it may surprise you to find out that
0:30	·	when Schroinger introduced the idea he
0:33	·	was talking about something else
0:34	·	entirely it is history that deserves to
0:37	·	be remembered
0:39	·	[Music]
0:42	·	it might seem surprising to a modern
0:44	·	audience but by 1900 the atomic theory
0:47	·	of matter that is that all matter is
0:48	·	made up of atoms was not fully explained
0:51	·	or even universally accepted while the
0:53	·	origins of the theory dated to the 18th
0:55	·	or early 19th century the exact nature
0:57	·	of atoms was still not understood
1:00	·	austrian physicist Ernst Mock whose
1:02	·	research on sound waves would lead to
1:04	·	naming the speed of sound Mach
1:06	·	proclaimed after an 1897 lecture that I
1:08	·	don't believe atoms exist mock argued
1:11	·	instead that atoms were just useful
1:12	·	mental concepts for explaining
1:14	·	observations but not real mock was just
1:17	·	one of a number of scientists who argued
1:18	·	against the atomic theory in the 19th
1:20	·	century despite some resistance research
1:23	·	on atoms continued to produce results
1:25	·	right at the turn of the 20th century
1:27	·	English physicist JJ Thompson's work on
1:30	·	electrons showed that the atom was not
1:31	·	the smallest form of matter at all and
1:33	·	in 1904 he proposed the first atomic
1:35	·	model with subatomic constituents his
1:38	·	model the plum pudding model would soon
1:40	·	prove incorrect but the discovery that
1:42	·	atoms themselves were made up of even
1:44	·	tinier pieces would be critical to the
1:46	·	formation of an entirely new field of
1:49	·	physics
1:50	·	problems with classical physics have
1:52	·	begun appearing in the 19th century when
1:53	·	traditional physics began failing to
1:55	·	explain certain phenomena there was for
1:58	·	instance the Gibbs paradox in which the
2:00	·	expression for entropy appears to
2:02	·	violate the second law of thermodynamics
2:05	·	other issues also cropped up such as
2:08	·	with thermal radiation when an object is
2:10	·	heated it becomes first red hot and if
2:12	·	it is heated further will emit other
2:14	·	colors first yellow white and then blue
2:16	·	as it emits light at shorter wavelengths
2:19	·	a perfect emitter like this would at
2:21	·	cold temperatures appear perfectly black
2:23	·	absorbing all light but emitting none
2:25	·	this ideal emitter was called a black
2:27	·	body and the radiation it emitted black
2:29	·	body radiation and while they could
2:31	·	explain experimental results at large
2:33	·	wavelengths at short wavelengths the
2:35	·	theories strongly disagreed with
2:36	·	experimental results and in fact
2:39	·	classical mechanics seem to predict that
2:40	·	at very short wavelengths energy would
2:42	·	be emitted at an infinite rate this is
2:45	·	called the ultraviolet catastrophe
2:47	·	physicists developed a second theory
2:49	·	that explained the results at short
2:50	·	wavelengths but which likewise failed to
2:52	·	explain the results at longer
2:54	·	wavelengths the issue was not trivial
2:56	·	and scientists sought a single theory
2:58	·	that explained all of the results
3:00	·	max Planck was the first to explain all
3:03	·	the results in 1900 with a new theory
3:05	·	instead of imagining that energy could
3:07	·	be admitted at any arbitrary amount he
3:09	·	proposed harmonic oscillators that were
3:12	·	in equilibrium with the thermal
3:13	·	radiation each of these oscillators he
3:16	·	said emitted energy only at a single
3:17	·	characteristic frequency the energy
3:20	·	emitted by any particular oscillator was
3:22	·	therefore quantized this idea would
3:24	·	become known as the plank relation and
3:26	·	the constant in the equation as plank's
3:29	·	constant
3:30	·	this was the first quantum theory in
3:33	·	physics and plank was awarded the Nobel
3:35	·	Prize in physics in 1918 for the
3:38	·	services rendered to the advancement of
3:40	·	physics by his discovery of energy
3:42	·	quanta it's difficult to overstate how
3:45	·	this understanding would transform
3:46	·	physics it was the foundation for the
3:49	·	theories that would solve many of the
3:50	·	issues in classical mechanics in 1905
3:53	·	Albert Einstein applied the theory of
3:55	·	quanta to a different issue in the late
3:58	·	1890s JJ Thompson had discovered
4:00	·	electrons but in 1902 Hungarian
4:02	·	physicist Philip Leonard was surprised
4:05	·	that the energy of electrons ejected
4:06	·	when light hits a metallic surface are
4:08	·	not related to the intensity of the
4:10	·	light as classical mechanics predicted
4:13	·	einstein suggested that for
4:14	·	instantaneous transitions of energy the
4:17	·	energy in light might occur in a finite
4:19	·	number of energy quanta in his 1905
4:23	·	paper on a huristic viewpoint
4:24	·	considering the emissions and
4:26	·	transformation of light Einstein wrote
4:28	·	that when a light ray is spreading from
4:29	·	a point the energy is not distributed
4:31	·	continuously over everinccreasing spaces
4:34	·	but consist of a finite number of energy
4:36	·	quanta that are localized in points in
4:38	·	space move without dividing and can be
4:40	·	absorbing or generating as a whole
4:43	·	albert Fosling a German physicist turned
4:45	·	scientific journalist called this
4:47	·	sentence the most revolutionary sentence
4:50	·	written by a physicist in the 20th
4:52	·	century this work is what earned
4:54	·	Einstein the Nobel Prize in physics in
4:56	·	1921
4:58	·	the quantum theory of light was followed
5:00	·	by the work of Danish theoretical
5:01	·	physicist Neils Boore who used quantum
5:04	·	theory to explain the emission spectrum
5:06	·	of atoms when gas is heated it emits
5:09	·	light at discrete frequencies bore
5:11	·	proposed a new model of the atom which
5:13	·	included quantized electron orbits this
5:16	·	created essentially our modern
5:17	·	understanding of the atom a dense
5:19	·	nucleus surrounded by orbiting electrons
5:21	·	that orbit at discrete orbits when the
5:23	·	electrons move from one orbit to another
5:25	·	they release photons at specific
5:27	·	energies creating emission spectrums all
5:31	·	these theories were really applied as
5:32	·	corrections to classical mechanics but
5:35	·	not as yet as their own field that
5:38	·	changed as physicists continued to
5:39	·	develop new explanations in 1924 French
5:42	·	theoretical physicist Lewis de Bruy
5:45	·	published the hypothesis that matter has
5:47	·	wave properties an idea that was proven
5:49	·	experimentally
5:51	·	two theories quickly followed the
5:52	·	development of matrix mechanics by
5:54	·	German physicist Wner Heisenberg Max
5:56	·	Bourne and Pascal Yordan and wave
5:59	·	mechanics developed by Austrianborn
6:01	·	theoretical physicist Irvin Schroinger
6:03	·	schroinger showed that the two mechanics
6:05	·	were in fact equivalent schroinger went
6:08	·	on to apply the concepts to the hydrogen
6:10	·	atom describing four properties of an
6:12	·	atom put together they described the
6:14	·	electrons quantum state multiple
6:16	·	physicists such as Boore and Heisenberg
6:19	·	attempted to explain the experimental
6:20	·	results in what became known as the
6:22	·	Copenhagen interpretation after Bo's
6:24	·	institute in the Danish city where
6:26	·	Heisenberg worked as an assistant no
6:28	·	actual definitive version of the
6:30	·	interpretation exists as the physicists
6:32	·	held a variety of differing opinions
6:34	·	there were some characteristic ideas
6:35	·	however such as that a system is
6:37	·	completely described by a quantum state
6:39	·	and that atomic interactions are
6:41	·	discontinuous others include the Bourne
6:44	·	rule of max Bourne which says that the
6:46	·	description of nature is essentially
6:48	·	probabilistic and Heisenberg's
6:50	·	uncertainty principle which states that
6:52	·	we can't know both the position and
6:54	·	speed of a particle with perfect
6:55	·	accuracy simultaneously
6:58	·	more complex is quantum superposition
7:00	·	which posits that a quantum system can
7:02	·	exist in multiple potential states until
7:04	·	a measurement is made when the wave
7:07	·	function collapses into one of those
7:08	·	states the Copenhagen interpretation was
7:12	·	far from universally agreed upon among
7:14	·	the most notable critics was Albert
7:15	·	Einstein himself einstein didn't have
7:18	·	issues with the experimental results but
7:20	·	doubted the conclusions of some others
7:22	·	like Boore and thought that quantum
7:24	·	mechanics remained an incomplete theory
7:26	·	the disagreements are highly technical
7:28	·	and have been repeatedly discussed among
7:30	·	physicists much of it sprung from the
7:32	·	idea that physicists like Boore and
7:33	·	Heisenberg believed their theory was
7:35	·	complete bourne and Heisenberg wrote in
7:37	·	1928 that the theory was a closed theory
7:40	·	whose fundamental physical and
7:41	·	mathematical assumptions are no longer
7:43	·	susceptible to any modification
7:46	·	einstein find that there were still
7:47	·	significant unanswered or
7:49	·	unsatisfactorily answered questions one
7:51	·	of the primary disagreements regarded
7:53	·	the implications about the construction
7:54	·	of reality according to Heisenberg
7:57	·	physical reality was only defined at the
7:59	·	moment of observation another issue
8:01	·	stemmed from Heisenberg's uncertainty
8:03	·	principle in 1935 a paper was published
8:05	·	under the authors Einstein Boris
8:08	·	Bidolski and Nathan Rosen which
8:10	·	challenged the idea that the theory was
8:11	·	complete entitled can quantum mechanical
8:14	·	description of physical reality be
8:16	·	considered complete and now generally
8:18	·	known as the EPR paper the paper
8:20	·	attempts to construct a thought
8:21	·	experiment paradox according to the
8:23	·	rules of the Copenhagen interpretation
8:26	·	this thought experiment imagined two
8:28	·	particles A and B which interact briefly
8:30	·	and then move off in opposite directions
8:32	·	according to the uncertainty principle
8:34	·	it's not possible to measure both the
8:36	·	position and momentum of particle B
8:38	·	precisely but you could measure the
8:40	·	position of a particle A according to
8:42	·	the paper finding the position of
8:44	·	particle A meant that you could
8:45	·	calculate the exact position of B and
8:48	·	finding the momentum of A the momentum
8:49	·	of B could be calculated the argument
8:52	·	was essentially that absent a direct
8:53	·	observation the momentum or the position
8:56	·	of particle B could be measured meaning
8:58	·	that there was a reality to those things
9:00	·	independent of their observation
9:02	·	this the paper argued meant that the
9:04	·	wave function does not provide a
9:06	·	complete description of the physical
9:07	·	reality bore objected and argued later
9:10	·	that year that the paper's reasoning was
9:11	·	faulty for Einstein's part in letters to
9:14	·	Irvin Schroinger he said that the paper
9:16	·	did not really represent his views and
9:18	·	that it was mostly written by Bolski he
9:20	·	said that the reality of particle B's
9:22	·	momentum or position is a sausage to me
9:25	·	a German saying meaning that he couldn't
9:27	·	care less instead he focused on the
9:29	·	issue of non-locality it made no sense
9:32	·	he thought that measuring particle A
9:34	·	could lead to two states for particle B
9:37	·	no matter how far apart they were
9:40	·	quantum states as it stood he thought
9:42	·	couldn't accurately reflect reality the
9:44	·	same year the EPR paper was published
9:46	·	Shreddinger wrote to Einstein to
9:48	·	congratulate him for challenging the
9:49	·	dogmatic quantum mechanics the
9:52	·	correspondence which continued was in
9:54	·	essence a series of critiques of Boore
9:55	·	and his school in August Einstein asked
9:58	·	Schroinger to imagine if the small-cale
10:00	·	mechanics physicists talked about were
10:02	·	enlarged suppose you had an unstable
10:04	·	barrel of gunpowder that had an equal
10:06	·	probability of exploding or not
10:08	·	exploding in the next year after a year
10:10	·	the mathematical equations in quantum
10:12	·	mechanics would cease to make sense as
10:13	·	they would describe a sort of blend of
10:16	·	not yet and already exploded systems in
10:19	·	reality Einstein said there is no such
10:21	·	intermediary between exploded and not
10:23	·	exploded troinger took that concept and
10:26	·	imagined his own scenario which he
10:28	·	called a quite ridiculous case confined
10:31	·	in a steel chamber is a geer counter
10:33	·	prepared with a tiny amount of uranium
10:35	·	so small that in the next hour it's just
10:37	·	as probable to expect one atomic decay
10:39	·	as none an amplified relay provides that
10:41	·	the first atomic decay shatters a small
10:43	·	bottle of pressic acid this and cruy a
10:47	·	cat is also trapped in the steel chamber
10:49	·	after an hour he said "Quantum mechanics
10:51	·	would say the living and dead cat are
10:53	·	smeared out in equal measure." Einstein
10:56	·	liked the thought experiment a wave
10:58	·	function that contains a living as well
11:00	·	as the dead cat just cannot be taken as
11:02	·	a description of the real state of
11:03	·	affairs einstein agreed writing to
11:05	·	Schroinger that nobody really doubts
11:07	·	that the presence or absence of the cat
11:09	·	is something independent of the act of
11:11	·	observation einstein also had some
11:13	·	philosophical disagreements regarding
11:15	·	the Copenhagen interpretation's idea
11:16	·	that quantum physics was essentially
11:18	·	probabilistic and not deterministic
11:20	·	famously he wrote in 1926 that God does
11:22	·	not play dice with the universe he
11:24	·	qualified the statement in a 1945 letter
11:27	·	writing that God tirelessly plays dice
11:29	·	under laws which he himself has
11:30	·	prescribed many have attempted in the
11:33	·	years since his death to better
11:34	·	understand his reservations and ideas
11:36	·	about quantum mechanics schroinger
11:38	·	published his famous cat thought
11:40	·	experiment in November 1935 in the
11:42	·	German magazine Natural Sciences he
11:44	·	almost withdrew it when the Jewish
11:46	·	editor of the magazine Arnold Berliner
11:48	·	was fired due to policies of the Nazi
11:50	·	government but decided to publish it
11:52	·	anyway at Berlin's request the point was
11:55	·	to highlight the incompleteness of the
11:57	·	model to critique the Copenhagen
11:58	·	interpretation but instead the thought
12:01	·	experiment has become part of the
12:02	·	foundation of quantum mechanics much
12:04	·	discussed in theoretical discussions
12:07	·	and to answer the obvious question no so
12:10	·	far as we know Irvin Schroinger did not
12:13	·	own a cat
12:15	·	boore didn't respond directly to
12:17	·	Schroinger's paper but the two continued
12:19	·	to correspond and in the end the
12:21	·	Copenhagen interpretation wasn't all
12:23	·	that bothered by the observations of
12:24	·	Einstein and Schroinger and actually the
12:27	·	concept that the cat can exist in two
12:29	·	states at the same time is now a
12:31	·	fundamental part of quantum mechanics or
12:33	·	at least at the quantum level scientists
12:35	·	have continued to test quantum mechanics
12:37	·	and the Copenhagen interpretation is
12:39	·	still the leading explanation for
12:41	·	quantum mechanics but the historical
12:43	·	irony is that Schroinger's cat is often
12:46	·	used to illustrate the counterintuitive
12:48	·	elements of quantum mechanics today and
12:51	·	the fact that he introduced the thought
12:53	·	experiment not to explain quantum
12:55	·	mechanics but to challenge it has
12:57	·	largely been forgotten
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