Hey there,

As a bit of a philosophical addendum to yesterday’s post about physics, I have a quick thought or two.

To recap, Brian Greene, physicist extraordinaire, says that despite the commonsense perceptions of people everywhere concerning everyday objects and their interactions with them, interactions which indicate that the future relies on the past and not the other way around, the quantum truth is quite the opposite. Using clever experiments and photons, scientists have proven (says Greene) that as far as quantum is concerned, the past is contingent upon the future. The past– that part of time which lies behind us (or in front of us, since that’s the only part we can see… never mind)- is contingent upon– conditioned by and dependent on- the future– that part of time which, in the classical mundane way of thinking, hasn’t happened yet.

And I don’t buy it. I mean, honestly, mixing up the future and the past? What’s next?  Where does it end with these people?

Actually, it’s got me thinking about how we classify reality. To give an example from a couple of hundred years ago: Some yuppie (or the contemporal equivalent) is in a bookstore in the 17th century when he happens to see a book by Galileo on the celestial bodies. He picks it up and flips to a random page, where he reads that, against all evidence to the contrary, the sun does not rise in the sky. Rather, the sun is the one motionless body in our solar system, and the planets all move around the sun, including the earth. What he sees when he looks east in the morning to see the sun creeping over the horizon is something like an illusion.

Is this young man wrong, then, to comment on the sun’s passage across the sky in a sonnet to his sweetheart? I don’t think so. He is describing the way that things really are- the sun really is moving across the sky, just as the sun truly is ‘anchored’ in the center of the system and the earth revolves around it. Both of these things are true, albeit true in different ways. Maybe it’s just a perspectival thing.

In the same way, I don’t think that any findings as can be found with these quantum experiments will cancel out the reality that seconds, minutes, and days wait their turn patiently to happen in a nice orderly manner, and nobody is contingent on anybody after them…

As my dear late grandmother said “Reality’s reality; it’s got to be what it is.” Or something to that effect.

-Daniel

Afternoon!

I wrote back in March about reading The Fabric of the Cosmos, by Brian Greene. Well, I’m still reading it, and it has me turned around as anything.

Right now I’m mired in the section on the flow of time and quantum, and I have to say, I’ve lost all faith in the scientific community. I just don’t know anymore. Let me see if I can enumerate my difficulty. By the way, if this is all too much for you but you want to know what I’m getting at, skip to the paragraph which begins with “Did you get that?”

In Chapter 7, “Time and the Quantum,” Greene talks about an experiment designed (I think) to determine whether light acts as a particle or a wave. A light source is set up in front of a mirror which allows light to pass through or to bounce off at a ninety-degree angle. Through some clever use of mirrors, the two waves of light are then directed toward the same detector film. Now, according to wave interference, the detector should look like the picture on the right, with bands of bright and dark. Interestingly, when the emitter is turned down so that it only emits one photon at a time, which means that it must either pass through the mirror or be reflected off of it, the interference pattern builds up in the same way- this, I believe, is what they call a probability wave. How that even happens I have no clue, since Greene later says that probability waves don’t exactly exist, not in the same way in which we think about things existing.

It gets worse when time comes in. See, the probability thing means that when a photon is emitted, it could go down either pathway from the splitter, which means that, until observed, it goes down both of them. Now, a detector can be set up which monitors one of the pathways, so we can know which one the photon actually went down. When that happens, we get a band more like the one below on the left. It seems that the act of observing the photon forces it down one path or another. When the detector is switched on, we get the image on below on the left; when off, we get the image above to the right.

Here’s where it get tricky (just kidding- we’ve passed through tricky and out the other side about three paragraphs ago): The detector can be programmed to switch on or off at random after the particle has passed through the splitter, and in that case, it appears that the photon has already ‘decided’ whether to be uncertain (right pattern) or certain (left pattern). The particle, at the splitter, cannot ‘know’ whether the detector is on or not; in fact, the detector hasn’t even decided whether or not to be on or off at that point. Nevertheless, in such a case the photon has already ‘decided’ to act in accordance with what we would expect, whether the detector is on or off. Greene says that “It’s as if the photons adjust their behavior in the past according to the future choice of whether the new detector is switched on; it’s as though the photons have a ‘premonition’ of the experimental situation they will encounter farther downstream, and act accordingly. It’s as if a consistent and definite history becomes manifest only after the future to which it leads has been fully settled” (The Fabric of the Cosmos, pp 188-89).

Did you get that? To sum up, in a random experiment wherein events can be manipulated to produce one of two results, the initial event (the photon’s ‘choice’ to go down one pathway or another) is uncertain until the second event (the detector’s random ‘decision’ to turn on or off) happens. In other words, the past is contingent upon the future, at least as far as quantum is concerned.

Even though Greene is a good enough writer to explain that experiment and its conclusions in such a way that I think I understand it, I still don’t believe it. How can I? The past isn’t contingent upon the future- that violates my concept of both past and future!

Anyway.

If this didn’t blow your mind, either I have explained myself poorly or you have no imagination. That’s all there is to it.