## On the Weirdness of Quantum Physics - Part I

Imagine look­ing down into a huge sports stadium, with its green play­ing field surrounded by empty stands and all seats avail­able to spec­ta­tors. Now add a human being stand­ing in the middle of the field, wonder­ing which avail­able seat to take, since s/​he is the first person there.

Your job is to predict which seat the spec­ta­tor will choose.

If you imag­ined the Saltlake Stadium in India, you would have 120.000 possi­ble seats to choose from, or if you’re think­ing smaller, like the Estadio Azteca in Mexico, you would only have 105.000 seats to eval­u­ate.

Still, as you can see, it can be very hard to predict exactly which seat the spec­ta­tor will select. Instead, let’s consider what’s most likely or prob­a­ble (in physi­cists terms).

For instance, it’s more likely that the spec­ta­tor will select one of the longer sides instead of the shorter ones (shorter walk, better view of the whole field). Depending on the sun, it’s more likely that the spec­ta­tor selects the shad­owy side for a better view and less heat. I also think it’s more likely that the spec­ta­tor wouldn’t walk all the way to the top, instead stay­ing close to the field, perhaps a row or four up for a better view, etc.

All this is more likely than not, but none of it more certain than other options, since we don’t know the spec­ta­tors pref­er­ences (unless you can read people’s minds, which I cannot).

Quantum physics is about prob­a­bil­ity, rather than certainty: You can calcu­late with great certainty where a cannon­ball lands depend­ing on amount of gunpow­der and angle of the cannon (clas­si­cal physics), but you cannot calcu­late with certainty where the spec­ta­tor sits down even­tu­ally (I will soon come to why this spec­ta­tor exam­ple is quan­tum physics.)

As soon as the spec­ta­tor makes a choice and starts to walk, we will imme­di­ately see in which direc­tion, and by study­ing where s/​he is look­ing, we will know some­thing about how high up in the stands s/​he ends up. This is clas­si­cal physics, case closed.

Now lets enter quan­tum physics: Before the spec­ta­tor begins to walk, we place a huge tent over the play­ing field, so all we can see is the tent and the stands that now surrounds the tent. We cannot see the spec­ta­tor any longer, however, we still know that s/​he is under the tent, ready to start walk­ing in some direc­tion.

The next thing that happens, is the strangest, weird­est, most bizarre phenom­e­non in quan­tum physics (if not the most bizarre thing in the universe):
As soon as the spec­ta­tor starts to walk, s/​he is all of a sudden visi­ble in all the avail­able seats in the stands! So if you chose the Saltlake Stadium in India, you now see 120.000 iden­ti­cal copies of the spec­ta­tor fill­ing every avail­able seat in the stadium. They don’t even look a little trans­par­ent (like ghosts), they are all real. In fact, so much so that if the 120.000 spec­ta­tor copies stood up on by one and started a wave sweep­ing around the stadium (they call it a prob­a­bil­ity wave in quan­tum physics), this wave would affect phys­i­cal objects, like turbu­lent air affect leaves, hot-dog paper, napkins, etc.

If we suddenly tore away the cover­ing tent, all the copies in the stands would disap­pear, and we would only see the orig­i­nal spec­ta­tor walk in a certain direc­tion, perhaps look­ing at a specific empty seat. Quickly add the tent again, and the 120.000 copies imme­di­ately fill the stands, creat­ing another wave (easy with the beer, please!)

In the real world this is just silly of course, but in the world of quan­tum physics, this is how the photon –the light parti­cle– works its magic. The “Stadium” story is my inter­pre­ta­tion of the well known “double-slit” exper­i­ment quan­tum physi­cists did on light, to decide if photons are indeed parti­cles, or if they are waves.

Part II will explain the double-slit exper­i­ment more closely (in this, hope­fully, under­stand­able way), but let me empha­size again: at the quan­tum level of real­ity, nature is spooky, real objects can be at many places at the same time, and all the iden­ti­cal copies can play with ‘itself’… It is said that if quan­tum physics doesn’t shake you up, you haven’t under­stood it!

Stay tuned, Part II will shake you up!

/​Finno