Reality is influenced by observation. Like in videogames.
London, 1801
At 48 Welbeck Street in London, a young scientist found shelter, in a rapidly expanding City.
London is transitioning in a new era, and it is due to become soon the world’s headquarters of
politics and finance. Life accelerates, in a striking contrast between the expansionist ambitions of
the government and the miserable living conditions of millions of people.
This is the story of Thomas Young (1773-1829), an "original genius”, as he will be later defined,
who gained notoriety mostly for his research on light and solid mechanics. Few people remember
he was also the first to find a method to translate the Egyptian hieroglyphs, contending this primacy
to an (according to him) usurper from beyond the Alps, Monsieur Champollion.
As a scientist, Thomas Young is also the first to openly challenge Newton's classical theory that
supported a fundamental assumption: that light consists of a stream of tiny fragments of physical
matter, or particles. Young, on the other hand, theorized the wave nature of light, asserting that
certain types of synergies would occur when two light waves meet each other.
To test this hypothesis, Young set up a simple yet brilliant experiment: he took a source of light
(electrons) and let it shine against a screen with two slits. Behind the screen, there was a detector
(like photographic paper or a photo diode). He observed and “interference pattern” of “bright”
regions (where lots of light or electrons were detected) and dark regions (where no detection
occurred).
This proved that light acts like a wave, but also to demonstrate that electrons can act like waves
creating interference patterns. Wait! Aren’t electrons particles? This is what Newton said, and
nobody had the nerve to say it was wrong. Therefore, Young’s theory was not immediately
accepted by his peers. Young’s response on this matter was as elegant as his theory: “Much as I
venerate the name of Newton, I am not therefore obliged to believe that he was infallible.”To better understand this experiment, called “Double Slit Experiment”, we will move to a tennis
field. This tennis field has got no net but a wall with two slits in it. Let’s start throwing tennis balls
at the wall.
As you might guess, some will bounce off the wall, but some will travel through the slits. Now, if
you put another wall behind the first, the tennis balls traveling through the slits will obviously hit
the second wall. Had you freshly painted the second wall, you could easily spot on it a distinct
pattern, that is, two strips of marks roughly the same shape as the slits.
Now let's go into the small world of Quantum. We will shoot tiny particles like electrons at our wall
with the two slits, blocking one of those slits off for the moment. Just like a tennis ball, some
electrons will pass through the open slit and hit the second wall. The pattern described on the wall
has roughly the same shape as the slits precisely like matter does on a large scale.
But here comes the twist: as we open the second slit, we would expect two rectangular patterns on
the second wall, just as if we shot tennis balls. What you actually see is a different thing: the spots
where electrons hit the wall mirror the interference pattern from a wave. To put it
bluntly, it’s like if you threw a fluid such as water and not tennis ball against the wall.
How on earth can this happen? Scientists thought they had the solution at fingertips: it is likely that
the electrons somehow interfere with each other, ending their route not in the same place as they
would if they were shot alone. As a proof of concept, scientists started to fire electrons one by one in a single line, so that they had no chance of interfering. Weirdly, even now each single electron
contributes as a dot to an overall pattern that still describes the interference pattern of a wave.
On second thought, scientists elaborated another theory. Can it be that each electron somehow splits
and passes through both slits at the same time, interferes with itself, and then recombines to meet
the wall as a single particle? Indeed, this appeared the only conceivable solution, doesn’t it?
Science, however, is not here to blame questions of honest seekers, so to find out the definite
answer, we will place a detector by the slits, to see where exactly the electrons pass through.
Much to our surprise, if you do that, then the wave-like interference pattern disappears from the
wall, and the particle pattern (as seen in the tennis field) shows up again !
Somehow, the very act of looking electrons traveling, safely guided them through the slits, like
well-behaved little tennis balls. Apparently, the electrons decided to act differently as if they were
aware of being watched and chose not to be caught in the act of performing their uncanny Quantum
affair.
Let's hire a detective to find a solution to this mystery: Leaving Welbeck Street, home of Thomas
Young, and crossing Blandford Street, we reach the renowned Baker Street 221B. It is precisely
there that brilliant mind of Sir Arthur Conan Doyle conceived the histories of the famous detective
Sherlock Holmes.
Knocking at his door, you would have found him in a dressing gown near the fireplace, reading the
latest news of crimes and misdeeds. Placing him the enigma of the double slit, he would have
commented, looking at you in a singular and introspective way:
First hypothesis: Is the electron able to perceive something? No, it isn’t as it lacks intelligence. It is
not able to "know" anything in the narrow sense of the term. We are on a false track. Who else is on
the crime scene? It’s us! That is, the person who is observing the experiment. We are the ones who
“transmit” to the electron the knowledge of the two possible ways to go through the slits and finally
to determine its trajectory. Welcome to the first basic principle of Quantum physics, that is:"We cannot observe the subatomic world (with eyes or other measurement systems) without altering
it. "
Phew! All this Quantum stuff was a near thing! What about some sleep before going with the
second shot of Quantum mechanics?
At 48 Welbeck Street in London, a young scientist found shelter, in a rapidly expanding City.
London is transitioning in a new era, and it is due to become soon the world’s headquarters of
politics and finance. Life accelerates, in a striking contrast between the expansionist ambitions of
the government and the miserable living conditions of millions of people.
This is the story of Thomas Young (1773-1829), an "original genius”, as he will be later defined,
who gained notoriety mostly for his research on light and solid mechanics. Few people remember
he was also the first to find a method to translate the Egyptian hieroglyphs, contending this primacy
to an (according to him) usurper from beyond the Alps, Monsieur Champollion.
As a scientist, Thomas Young is also the first to openly challenge Newton's classical theory that
supported a fundamental assumption: that light consists of a stream of tiny fragments of physical
matter, or particles. Young, on the other hand, theorized the wave nature of light, asserting that
certain types of synergies would occur when two light waves meet each other.
To test this hypothesis, Young set up a simple yet brilliant experiment: he took a source of light
(electrons) and let it shine against a screen with two slits. Behind the screen, there was a detector
(like photographic paper or a photo diode). He observed and “interference pattern” of “bright”
regions (where lots of light or electrons were detected) and dark regions (where no detection
occurred).
This proved that light acts like a wave, but also to demonstrate that electrons can act like waves
creating interference patterns. Wait! Aren’t electrons particles? This is what Newton said, and
nobody had the nerve to say it was wrong. Therefore, Young’s theory was not immediately
accepted by his peers. Young’s response on this matter was as elegant as his theory: “Much as I
venerate the name of Newton, I am not therefore obliged to believe that he was infallible.”To better understand this experiment, called “Double Slit Experiment”, we will move to a tennis
field. This tennis field has got no net but a wall with two slits in it. Let’s start throwing tennis balls
at the wall.
As you might guess, some will bounce off the wall, but some will travel through the slits. Now, if
you put another wall behind the first, the tennis balls traveling through the slits will obviously hit
the second wall. Had you freshly painted the second wall, you could easily spot on it a distinct
pattern, that is, two strips of marks roughly the same shape as the slits.
Now let's go into the small world of Quantum. We will shoot tiny particles like electrons at our wall
with the two slits, blocking one of those slits off for the moment. Just like a tennis ball, some
electrons will pass through the open slit and hit the second wall. The pattern described on the wall
has roughly the same shape as the slits precisely like matter does on a large scale.
But here comes the twist: as we open the second slit, we would expect two rectangular patterns on
the second wall, just as if we shot tennis balls. What you actually see is a different thing: the spots
where electrons hit the wall mirror the interference pattern from a wave. To put it
bluntly, it’s like if you threw a fluid such as water and not tennis ball against the wall.
How on earth can this happen? Scientists thought they had the solution at fingertips: it is likely that
the electrons somehow interfere with each other, ending their route not in the same place as they
would if they were shot alone. As a proof of concept, scientists started to fire electrons one by one in a single line, so that they had no chance of interfering. Weirdly, even now each single electron
contributes as a dot to an overall pattern that still describes the interference pattern of a wave.
On second thought, scientists elaborated another theory. Can it be that each electron somehow splits
and passes through both slits at the same time, interferes with itself, and then recombines to meet
the wall as a single particle? Indeed, this appeared the only conceivable solution, doesn’t it?
Science, however, is not here to blame questions of honest seekers, so to find out the definite
answer, we will place a detector by the slits, to see where exactly the electrons pass through.
Much to our surprise, if you do that, then the wave-like interference pattern disappears from the
wall, and the particle pattern (as seen in the tennis field) shows up again !
Somehow, the very act of looking electrons traveling, safely guided them through the slits, like
well-behaved little tennis balls. Apparently, the electrons decided to act differently as if they were
aware of being watched and chose not to be caught in the act of performing their uncanny Quantum
affair.
Let's hire a detective to find a solution to this mystery: Leaving Welbeck Street, home of Thomas
Young, and crossing Blandford Street, we reach the renowned Baker Street 221B. It is precisely
there that brilliant mind of Sir Arthur Conan Doyle conceived the histories of the famous detective
Sherlock Holmes.
Knocking at his door, you would have found him in a dressing gown near the fireplace, reading the
latest news of crimes and misdeeds. Placing him the enigma of the double slit, he would have
commented, looking at you in a singular and introspective way:
“My dear friend, once you have eliminated the impossible, whatever remains, however improbable, must be the truth” (Sherlock Holmes in The Sign of the Four, 1890)
First hypothesis: Is the electron able to perceive something? No, it isn’t as it lacks intelligence. It is
not able to "know" anything in the narrow sense of the term. We are on a false track. Who else is on
the crime scene? It’s us! That is, the person who is observing the experiment. We are the ones who
“transmit” to the electron the knowledge of the two possible ways to go through the slits and finally
to determine its trajectory. Welcome to the first basic principle of Quantum physics, that is:"We cannot observe the subatomic world (with eyes or other measurement systems) without altering
it. "
Phew! All this Quantum stuff was a near thing! What about some sleep before going with the
second shot of Quantum mechanics?
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