To begin with, can light be fired as particles? (Part 2)
🌟Click here for "What is so amazing about the double-slit experiment? (Part 1)"💁♀️
🤖: That's a good question, BLUE.
This is the core part where many people get stuck, thinking, "Wait? Can you fire light as particles?" So, let's break it down at a level even an elementary school student can understand, but without cutting corners.
First, let's start with the conclusion 🌱
🤖: 👉 Yes, technically, it is possible to emit light "almost one particle at a time."
However, that is,
not like the feeling of "throwing beans one by one"
"slicing light tears into individual drops over time"
which is a quantum-like way of doing things.
① To begin with, light is a "tear (wave)," so how can it be one particle?
🤖: BLUE's question is very fundamental.
Light is originally a wave, so
why can it be emitted "one particle at a time"?
What's important here is 👇
✔ Light is
an "energy in the form of a wave," but the amount exchanged is a particle (photon).
That is what kind of existence it is.
🌊 It has the shape of a wave
🍬 But it is exchanged one particle at a time
It is a somewhat mysterious existence that is both.
② The old way: The problem with just making it darker
In the initial experiments,
a halogen lamp (which is always on)
was made progressively darker.
This method was used.
To visualize it👇
🌧 It is raining heavily
→ Gradually make it a light rain
→ Only a few drops fall per second
With this,
they thought,
“It must be one drop at a time now.”
❗ But there was a problem
Since light is a wave,
a single particle might be stretched out thinly
actually, the photons before and after might be overlapping
In other words,
“Is it really just one particle?”
This doubt remained.
③ Solution: “Cut” the light by time💡
That is where
short-pulse light came in.
This is,
✨ a technology that
“flashes”
the light for just an instant
technology.
🔹 To put the numbers simply
Duration of light:
40 picoseconds
👉 40 trillionths of a second (almost an instant)Length of light:
approx. 12mm (about the width of a finger)Distance to the next light:
30m (about the length of a school pool)
In other words👇
📏 A 12mm chunk of light
🏃♂️ separated by 30m each
pop, pop, pop...
flying along
Calculation of the distance light travels in 40ps (picoseconds)🧮
Speed of light: The speed of light in a vacuum is approximately 300,000 km/s, or about 3 × 10⁸ m/s.
Convert picoseconds (ps) to seconds: 1 ps is 1 trillionth of a second (10⁻¹² seconds).
Distance calculation:
First, express the distance traveled in one second in meters: approx. 3 × 10⁸ m/s.
Next, convert 40 ps to seconds: 40 ps = 40 × 10⁻¹² seconds.
Use the formula: Distance = Speed × Time :
Distance = (3 × 10⁸ m/s) × (40 × 10⁻¹² s)
Distance = 120 × 10⁻⁴ m
Distance = 0.012 m
Convert meters to centimeters:
0.012 m is equivalent to 1.2 cm (12mm).
This extremely short time scale is used in fields such as ultrashort pulse laser processing. ☺️
Calculation of the time it takes for light to travel 30m🧮
Time = Distance ÷ Speed
Time = 30 meters ÷ 300,000,000 meters/second
= 0.0000001 seconds
Expressed in nanoseconds (ns),
it is about 100 nanoseconds (100ns).
This is a super important point 🌟
👉 The light pulses never overlap
Therefore,
the preceding light and the following light
cannot cooperate to interfere
—that excuse is completely off the table.
④ Dimming it even further
Within this short chunk of light,
we weaken it further until it reaches a state where
there is either
one photon or none at all.
This is the state we aim for.
Then👇
🎯
“This pulse has a high probability of containing only one photon”
This creates a
single-photon state
.
We have succeeded for the first time in the world in electrically generating single photons at room temperature using artificial diamonds. -2012.4.16-
~Accelerating toward unhackable quantum cryptographic communication~
https://www.jst.go.jp/pr/announce/20120416/index.html
⑤ Even then, interference fringes appeared 😳
If you perform a
double-slit experiment under these conditions...
✔ Same as continuous light
✔ Striped patterns appeared
In other words,
👉 Only one photon particle
👉 And it is not overlapping with others
👉 Yet it still interfered
The following is the case for electrons, but even though electron particles are fired one by one, if you keep firing many of them, interference fringes gradually become visible.
⑥ What does this mean?
It means this👇
Photons are
not "small balls"But
they are also "spread-out waves"
To be precise,
🌀 While spreading as a wave,
📍 it is detected as a single point
Existence.
⑦ In a BLUE-like analogy 🌌
Photons spread through the world in the shape of a tear, but
the moment they touch the world, they wet the cheek as a single drop.
※Touching the world means leaving information in the world
At this moment, the wave nature disappears, and light appears as a particle.
This short-pulse technology is
👉 like a dropper that releases those tears one drop at a time.
⑧ So, is 'firing one particle at a time' really being done?
✔ It is not completely 100% 'definitely one particle'
✔ But physically, it creates a situation where
it can only be thought of as having one particle.
In science, this is called
a single-photon source
.
Bonus
Captured the movement of light in slow motion!
The photos capture a video of light traveling from right to left.
In 1 picosecond (ps), light travels 0.3mm
In 1.78ps, light travels 0.534mm
Until the light at the right edge reaches the light at the left edge
1.78ps/frame x 5 photos = 8.9ps
The distance light travels in 8.9ps is
0.3mm/ps x 8.9ps = 2.67mm
🌱 Summary at the end
Light is a wave, but
the transfer of energy is a particle
Technically,
by separating time and space,
it can be handled almost 'one particle at a time'
Even so,
photons interfere with themselves
Therefore, the double-slit experiment is
not about "consciousness" but
a matter of information and probability
<<FIN>>
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