Assignments
• Watch Cosmos: Possible Worlds, Episode 9, "Magic Without Lies".
• Read and think about I dwell in Possibility, by Emily Dickenson.
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• Submit your questions and comments for discussion, using the form at the bottom of this or any page at Discuss Cosmos: Possible Worlds. Be sure to mention that your contribution pertains to Episode 9.
To think about
• On the smallest scale, it appears that the mere act of observation, or the possibility of observation, changes the outcome of events like the two-slit experiment of Thomas Young.
• It has been said that Young's experiment captures the full range of quantum paradoxes.
• The world revealed to us by our senses is a common-sense world, where the logic of cause-and-effect applies. On the other hand, the quantum world precisely obeys quantum mathematical laws, and often -- no, I should say usually, maybe even always -- those laws seem to defy common sense, and wreak havoc with our notions of cause-and-effect. At what scale is the boundary between these worlds ? In other words, at what scale does lawful but mysterious physical behavior becomes simply (but not always simple) cause-and-effect?
Read this poem about fuzzy boundaries:
Because You Asked about the Line Between Prose and Poetry, by Howard Nemerov
• At 42:00, Neil DeGrasse says, "We still don't know how a photon can be a particle and a wave at the same time. What I love about science is that it demands of us a tolerance for ambiguity. It requires us to live with humility regarding our ignorance, withholding judgment until the evidence comes in."
• At 15:44 and following, pause and look carefully at the depictions of photons. What properties of photons can you imagine being depicted by those colorful cartoons? Compare with the wave depiction of light at Wikipedia's entry, Electromagnetic Radiation, at the beginning of the section, "Properties". Think about what's right and what's wrong with each depiction. Is there a single best way to depict light?
• Repeatedly, Tyson says that we "still don't understand" the quantum world. What are the prospects for "understanding" quanta?
• What does Tyson mean when he says, "Science is the struggle to imagine and find above."
Questions for Discussion
Student questions will appear here
In this episode, Tyson talks about space and dimensions of space. What is a dimension? In our discussion of Episode 8, a student mentioned the shape of space, Gauss's attempts to see if space is flat or curved, and they later sent me this: Gauss and Shape of Space
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Also regarding discussion of Episode 8:
A student writes: Here's a question that was in my mind when class ended. After the Sagan Cosmos segment ended there was a comment that Sagan's view represented the rational perspective. Some said that there's also an emotional perspective supported in part by evolutionary biologists. Then someone said that the vastness of the video made him think of a third perspective; the spiritual perspective. What is the difference between the emotional and the spiritual perspective?
Maybe this essay could lay some solid ground for discussion of such ideas: Realms of Belief
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Regarding Episode 9
What do we really mean by observation; is it one human being with two eyeballs looking at it?
Is there some lesser or greater amount of observation that would have a difference? I am having trouble getting my head around the concept of observation, I mean my my dog could be sitting there observing.
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Of course this episode keeps you scratching your head because that is exactly the state of anyone who is trying to understand the quantum nature of light - just like the Flatlander trying to understand "above." My personal solution is to listen to descriptions of the experiments over and over. One of my favorite sites for physics videos is Veratasium. Here are the links to his videos about light as a wave (duplicating Huygens double-slit experiment using sunlight): https://youtu.be/Iuv6hY6zsd0
And light as a particle: https://youtu.be/GzbKb59my3U
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have been reading Richard Rhodes, "The Making of the Atomic Bomb" and he supplied me with the answer to a question I had after watching the Veratasium video about the particle nature of light. The Question: "How was it suggested (proved?) that light was a particle before a sophisticated detector and laser like Derek Muller uses in the video existed?" HINT: Einstein got the Nobel for this.
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I found this quote: “ John Wheeler, too, used a variant of the double-slit experiment to argue that “no elementary quantum phenomenon is a phenomenon until it is a registered (‘observed,’ ‘indelibly recorded’) phenomenon.” My question is: what exactly does “registered” mean here? It sounds pretty squishy.. [ added by GR: see Wheeler's Delayed-Choice Experiment and the brief description below in Added Resources. ]
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Episode 9 plays on limits of human perception to (in my opinion) sensationalize science. As humans we are (as pointed out) locked in three dimensions. We can make mathematical and science models in higher dimensions but we cannot process them as aspects of our sensed world. A result is that we fall back on things we know or sense - particle? or wave? - to manufacture conundrums. There is a level of reality (beyond human interpretation) that we cannot get to. Like Plato’s shadows on the wall, all we have ultimately are shadows even if they are magnificently magnified by experiments and models.
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The conundrum of the paired photons is another example where we as humans may never be able to make gut sense it. Our senses cannot grok gravity “acting at a distance” even though Einstein explained it in terms of a certain metric in a certain higher dimensional space. Photons appear to be acting on each other at a distance, but that does not rule out an explanation, be it impenetrable to our human limits in sensing the world.
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As they 'used to say' at the end of the country-music radio and TV shows of the later forties and early fifties, "Keep those cards and letters comin' in, folks !"
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Other Resources (optional)
I might use material from these sources in class.
• Electromagnetic Radiation, at Wikipedia
• Fun with four dimensions, in this short story: "-- And He Built a Crooked House", by Robert A. Heinlein
• Can a Computer Devise a Theory of Everything?
• Wheeler's Delayed-Choice Experiment
One of the most fascinating ideas about the particle-wave duality of objects that obey quantum laws (quanta, such as photons and electrons) is John Wheeler's delayed-choice experiment, actually a set of thought experiments.
From Wikipedia: "These experiments are attempts to decide whether light somehow "senses" the experimental apparatus in the double-slit experiment it will travel through and adjusts its behavior to fit by assuming the appropriate determinate state for it, or whether light remains in an indeterminate state, neither wave nor particle, until measured."
The Wikipedia entry provides a full description of John Wheeler's thought experiment about simultaneous wave-particle behavior, and examples of delayed-choice experiments.
• Beam splitters and how they work (Wikipedia)
Beam splitters are employed in some versions of delayed-choice experiments. This entry contains of list of famous experiments that employ beam splitters.
• A Do-It-Yourself Quantum Eraser !
The May 2007 edition of Scientific American provided instructions on using simple apparatus for seeing quantum interference and demonstrating how observation changes the outcome of quantum experiments. Seeing interference is surprisingly easy. The other experiments are more challenging, but it you are good with your hands, you might pull them off. In addition to common household items, you will need a couple of odd items: a laser pointer, and polarizing film.
