Things you think you know but you are wrong

If you are going to come along with me then you are going to have to accept the fact that there are things you think you know, assumptions that make sense for you and which have worked in your life, but assumptions that are just plain wrong.

I want to take a little time giving an example of common assumptions about reality that are useful but completely wrong.  And yeah, for those who have taken notice of certain cultish religions this does sound a little like a pitch for them, but I promise that is not what this is.  I am not talking about spiritual things here, I am talking about cold hard reality.

I assume you have all seen optical illusions, and you all accept the fact that sometimes, in some situations, what you think you see is not actually what is there.  As scientists are finding out more and more about how our brain does visual processing, they are starting to find out some interesting things.  For example, you all know about our blind spot and how it works.  You've probably seen demonstrations of your blind spot.  I learned about it back in high school.  What I did *not* know until recently, though, is that our brains actually 'fill in' the blind spot with what we see around the blind spot.  I think this even applies to an edge that we see going through the blind spot.  We will see an unbroken line going through the blind spot.  Our brain fills in the blank and we see what may not, actually, be there.

Moving on from our blind spot, let us go on to the act of throwing and catching a ball.  When I was younger I greatly enjoyed playing baseball, and I still love coaching and playing softball.  When I throw a baseball I look at the receiver's glove and I try to throw the ball straight to the glove.  If I am really good I can come pretty close.  A major league pitcher may have "pin-point" accuracy, meaning they can throw to an area maybe a foot wide in each direction.

Did you notice what I said though?  I used 'they' as the third person singular pronoun for indeterminate gender when I should have used 'he/she'.  That usage of 'they' used to really bother me, and it is still an incorrect usage, but I have almost totally given in to the current usage.  I know why the usage is changing, we used to use 'he' but that assumes too much and we simply do NOT have a good word to use for the third person singular pronoun, and I also know that good writers should write around the problem, but those people are dying off, and I concede to the change, even though it is simply incorrect.

But what I really meant with my questions is did you notice that I said I throw the ball _straight_ to the glove, but clearly that is not the path the ball takes.  The ball takes an arc, pretty much a parabola, rising up and then dropping down.  In addition, good pitchers can curve the ball even more, and plenty of batters have swung as best they can at where they think the ball is and have missed the ball, so obviously they did not really know where the ball was.

Even if all we know is that the ball starts at my hand and eventually hits the catcher's mitt, we still think we know the path the ball takes.  Maybe we use the wrong word like "straight" but we know, in our gut, that a baseball leaving my hand must have followed an arc to get to the catcher's mitt.  If we watch from first or third base we can see the arc of the ball without much trouble.  But think about that.  For us to know that the ball travels an arc we have to see it along the way.  If we had a screen up hiding the flight of the ball, and if all we could see was the pitcher releasing the ball and then the catcher catching it, we would assume that the ball traveled the arc because we have seen that a million times, and maybe we have even measured the force of gravity and we can predict, with great accuracy, where the ball is even if we do not see it.  So even when we cannot actually see every single position of the ball along the way, we know the path of the ball.  We know it so well we have the science of ballistics and aeronautics and we can predict with extreme accuracy the path of a projectile and the orbit of a satellite.  Up here, at the macro level, we 'know' stuff even when we don't really observe it.  We make assumptions, and a lot of times we make assumptions without even knowing it, and that usually works out pretty well for us, although that is a topic big enough for another post.

Moving on to the quantum level though, where the moving objects are extremely tiny, a lot of our assumptions are just plain wrong, and that is pretty cool, because it gives us a puzzle with an absolute answer as well.  It gives us an interesting problem to think about, a puzzle that has an objective answer, and that is worth a fortune.

At the quantum level there are only a couple ways and times when we can 'see' an object.  There are ways to do it, take my word for it, but unlike big things like a baseball at the quantum level we pretty much can only get brief glimpses of quantum things with a lot of blind spots in between.

The quantum phenomena that really got my attention back in my youth was an experiment that can be done with photons.  Photons are one of the basic objects way down at the quantum level, and for right now as a simplification let's just talk about the photons that are the smallest bit of visible light.  Some of the things that can happen to these photons are creation, movement, interaction with other quantum objects, and destruction.    From way up here at the macro level, studying optics, we know that light more or less goes in a straight line, it can be reflected, it can be refracted, and it can be absorbed by matter.  We know other stuff about it too, a lot, but forget about that for now.

Here is the experiment:  Say you have a light source and you shine it onto a semi-silvered mirror.  By that I mean a piece of glass that has a partial mirror surface on it, like the 'two way' mirrors they use in stores to observe people to make sure they are not stealing.  Assume that the mirror lets half the light through and the mirror reflects the other half.  Assume we angle the mirror so that some of the light is reflected and the rest of the light is refracted through the glass.  By the way, this is a real experiment that really has been done zillions of times.

So far I admit this is rather boring, but stick with me.  What if use semi-silvered mirrors to split the light beam into two parts which each take separate paths but then the separate beams get recombined later by using another semi-silvered mirror?

How can we do this?  We take the reflected beam of light, the part that reflected off the semi-silvered mirror, and we reflect that beam again with full mirrors a couple times so that it goes out and then back in again and it gets combined with the original beam by using another semi-silvered mirror.  I can't draw the diagram for this, but the light that is reflected by the first semi-silvered mirror takes a left, then a right, goes parallel to the original beam, and then takes another right, then into a final semi-silvered mirror where it is reflected and re-joins the original beam.  The part of the original beam that is refracted through the first semi-silvered mirror goes straight for a distance and then through another angled semi-silvered mirror, where it combines with the detoured beam.  Think of the light as a marching band going down a street, then some of the band takes a detour to the left for a block, turns right and goes down a parallel street for a couple blocks, and then turns right and then left again to join the rest of the band that had walked straight and never turned.

One of the interesting aspect to light is that, since 1909 or so, it was known that while light moved and bounced like a stream of tiny particles, it also had some wave-like properties.  Specifically when light passes through a slit in a barrier the light that comes through on the other sides shows interference patterns.  These interference patterns happen when waves interact, and viola (yeah, I know, puns and all that), light flies like an arrow and bounces like a ball and has interference patterns like a wave.  For a long time, even up to the time when I was born in the 1950s, there was a debate about whether light was a wave or a particle.  (As an aside, it is good to know that a 'false dilemma' is a classic logical fallacy.  Keep your eyes open for them.) The debate is now over.  The 'particle or wave' thing is a false dilemma.  Photons are neither, they are a localized waveform that has the properties of both a wave and a particle.  How stupid were we to think light had to be either a wave or a particle?  We were like the Greeks saying "Earth Air Water and Fire."  But I digress.  Back to our experiment.

We split the light, then recombine it, and then pass it through a slit, and we see interference patterns just as if the light had not actually been split at all.  Well, you say, what is the big deal?  And you are right,  it is not really a big deal - we have shown that photons can interact with each other to form interference patterns.  We already knew that.  And also, did you notice the two ways a photon could escape from our experiment?  I forgot to mention that, but those paths don't really matter.

The mind blowing thing is this.  What if we change the photon generator in our experiment  in such a way that it sends out not a gazzilion photons in a beam, but a single photon at a time.  Can we do that?!  Oh yeah, we can do that.  People have done this.

Let us follow a single photon instead of a beam of photons.  We are able to detect when a single photon is created and emitted.  Can we tell if it is reflected or refracted through the first semi-silvered mirror?  Oh yeah, we can do that, by placing detectors in each of the paths, and when we do that we will see that the photon is either detected on the reflection path or on the refracted path through the first mirror, one path or the other.  Trust me.  The photon is detected either on one path or on the other, and never on both paths at the same time.  This experiment has been done a zillion times, but so what, this is about as interesting as flipping a coin and seeing that half the times it is heads and half the time it is tails, and never both at once.  Exactly so.  This is boring, but what is not boring is the fact that if we remove the detectors and let the photon pass all the way through the slit at the end, taking only one path or the other but never both guess what?  We will see an interference pattern at the end.

No lie.

A single photon takes one of two paths, paths which for all I know could be very long paths and of differing lengths, and yet when that photon goes through the final slit it will show an interference pattern. 

Go ahead, say it - WTF?!!  Interference patterns are caused by photons interacting with each other.  Also, there is no such thing as half a photon.  There just isn't.  Quantum means no halfsies any more.  Things are divided this far and no further.

This is pretty much what I learned back in the Seventies.  I'm pretty sure that is all we knew back then, or at least it was all I could get in a college level text book at the undergraduate level.  Keep in mind this was pre-internet, and at the time I was looking at some other really cool things that could make me money, so at the time I didn't really dive very deeply into this.

This is one of the questions which I set aside and which gnawed at me off and on for over thirty years.  I'm pretty sure I know we now have an answer for this, and I'm pretty sure I know what the answer is,
but I need to save that for another post.

Can anyone else see why this is such a great puzzle to work on?