Pratica di Shadowing: The Uncertainty Principle: What Does It Mean, How Does It Work? - Impara a parlare inglese con i video
Creazione lezione...
1
If you know one thing about quantum mechanics, then that's more than most people, and it's probably that it's got something to do with the uncertainty principle.
2
But just exactly what does that mean and how does it work?
3
That's what we'll talk about today.
4
Werner Heisenberg was the first to understand that quantum mechanics sets limits to what we can know.
5
Yes, even for string theorists.
6
Some properties of quantum particles can't be determined precisely at the same time.
7
And it's not because we're not good at measuring, it's just how nature is.
8
The best known example is the position and momentum of an object.
9
You can think of the momentum as the velocity multiplied with the mass.
10
This isn't correct for massless particles, but for our purposes it'll be good enough.
11
Let's just pretend that massless particles don't exist, it shouldn't be too hard.
12
Quantum mechanics says that you can't measure both the position and momentum precisely.
13
This means if you know precisely where a particle is, you don't know which direction it's going.
14
And the other way around, if you know which direction it's going, you don't know where it is.
15
The position of a particle is usually denoted with x and the momentum with p.
16
The uncertainty in each is marked with a large delta in front of the variable.
17
So delta x is the position uncertainty and delta p is the momentum uncertainty.
18
Heisenberg's uncertainty principle then says that the product of those two is always larger than a constant h -bar divided by two.
19
This means if one of those uncertainties gets very small, then the other one must be very large, otherwise the inequality would be violated.
20
This is where the joke about Heisenberg comes from, where he gets stopped by police who tell him how fast he was driving, and Heisenberg says, great, now I'm lost.
21
But what does it mean that you can't measure the position and momentum with certainty at the same time?
22
Does it mean that if you come with two detectors, a lightning strike will explode one of them?
23
Well, no. The uncertainty principle doesn't say that you can't measure both of those quantities.
24
It shows that you can't measure both precisely.
25
If you've pinned down one, then the other will have a large spread.
26
This means if you repeat the experiment, the result will be all over the place.
27
It's the statistical uncertainty of this series of measurements that becomes large.
28
A good example of this is letting quantum particles go through a narrow opening.
29
The quantum particles act like waves, so this will create an interference pattern on the screen.
30
This pattern is built up of single particles.
31
The particles don't all collect in one place.
32
And that's because you know the particles went through the slit, so you know something about their position.
33
Then you can't tell which direction they are going.
34
But of course, once a single particle hits the screen, you know which direction it went.
35
What the uncertainty Uncertainty principle means is therefore that if you repeat this for many particles, then the outcome has a broad distribution.
36
Another example is the relation between the uncertainty in energy and time.
37
Consider you have a fluorescent sticker, the kind of stuff that glows in the dark.
38
You put it into light and then, for a few hours afterwards, it'll emit light of a particular color, usually it's some shade of green.
39
The way this works is that the light
40
which falls on the sticker kicks off an electron from its normal energy level into a higher level.
41
In most materials, the higher electron levels are extremely unstable.
42
The electron falls back down immediately, and in that process the photon is emitted again.
43
In fluorescent materials, however, the electrons can stay there for a few hours.
44
It's called a metastable state.
45
And only when the electron falls down will the light be emitted again.
46
As a consequence the sticker glows for some hours.
47
But just exactly how long do the electrons stay in that higher energy level?
48
Ah, well, you can't say exactly.
49
You can only talk about the probability of it dropping down in a certain amount of time.
50
And why is that?
51
It's because you know something about the energy of the electron on.
52
It's sitting on this meta -stable level.
53
Consequently, you can't know exactly how long it stays there.
54
Such is life you can't have at all.
55
This is basically also how nuclear decay works, by the way.
56
Finally, the uncertainty principle has its origin in the properties of waves.
57
It comes about because in quantum mechanics particles can act like waves.
58
What's a wave?
59
A wave is something that changes periodically in space and time.
60
That could be water waves, electromagnetic waves, sound waves, or even a Mexican wave when a sports game gets boring.
61
Waves have a wavelength and a frequency that's inversely proportional to the wavelength.
62
The frequency tells you how much change there is in a certain period of time.
63
If you have a perfectly regular sound wave, then it would sound like a beep at one particular frequency.
64
But most sound signals aren't that simple.
65
For example, here's me singing an A.
66
This isn't just one frequency.
67
You can take this sound apart and you'll find that, for one thing, I'm not a computer chip, so I don't exactly hit the A.
68
But also, the way the human voice box works, it has a lot of higher harmonics.
69
This breakdown of sound into all the frequencies it contains is called a spectrum.
70
This doesn't only work for sound, but for every distribution of anything really.
71
You can calculate a spectrum of the distribution of people in a room if you want to, and I'm sure somewhere there are businesses doing just that.
72
But a more relevant example for us is light.
73
If you have light of one particular wavelength, then that'd be one particular color,
74
and the spectrum of this light would have one single peak at one particular frequency.
75
Technically, for the spectrum to be exactly one frequency, the light wave would have to keep on waving forever.
76
We never deal with that in reality.
77
In reality, the light we deal with is bunched.
78
It passes by within a certain window of time.
79
First it wasn't there, then it was there, now it isn't there again.
80
Like money on my bank account.
81
Physicists call this a wave packet.
82
How do you pack waves?
83
Especially without getting wet?
84
The curious thing about waves is that they can interfere both constructively and destructively.
85
If they interfere constructively, they add up.
86
If they interfere destructively, they can cancel each other out.
87
If you overlay many of them in just the right way, you can do this so that outside of some region of space and time, the interference is almost completely destructive,
88
and you are left with a constructive interference in just a small region.
89
A wave packet is an overlay of different wavelengths and therefore an overlay of different frequencies with the correct offset.
90
Such an overlay, by the way, is called a superposition.
91
Sounds familiar?
92
Yes, we do use superpositions in quantum mechanics.
93
And this is where the word comes from.
94
It comes from adding different wavelengths together.
95
You superpose them.
96
Okay, now here's the thing.
97
As we just saw, we have two ways to describe the same wave packet.
98
You can either say it's this distribution in time, wasn't there, was there, isn't there again,
99
or you can say it's this distribution of frequencies with these offsets.
100
They both describe the same thing, the same wave packet.
101
There is a mathematical procedure to calculate one from the other.
102
It's called a Fourier transformation.
103
Put in a distribution in time, the Fourier transformation will give you the spectrum.
104
Put in the spectrum, the Fourier transformation will give you the distribution in time.
105
Here's the kicker.
106
If the one distribution is sharply peaked, say you have a flash of light that's just a brief moment in time,
107
then that means that it must contain a lot of different frequencies.
108
The spectrum is very spread out.
109
And the opposite is also true.
110
If you have something with a very narrow frequency, then it must be spread out in space.
111
Now you can ask, what's the relation between the spread in these two distributions, the one in time and the one in frequency?
112
And would you know it, they're related to each other by an inequality that looks pretty much like the uncertainty principle.
113
Whoa, but wait, this had nothing to do with quantum mechanics.
114
We were just talking about spectral analysis.
115
So what is going on?
116
What's going on is that while this looks like the uncertainty principle, it's not.
117
This is a property of waves.
118
It relates a spread in time with the spread in frequency.
119
To get Heisenberg's uncertainty principle, you further have to identify a frequency with an energy.
120
Or if you do it in space, you have to identify the wave vector with the momentum.
121
And this is where the H bar gets in.
122
We learned this from no other than Albert Einstein.
123
Yes, that guy again.
124
He pops up more than toast in a student house.
125
It's actually what he won the Nobel Prize for.
126
No, seriously.
127
Albert Einstein didn't win the Nobel Prize for special or general relativity.
128
He wanted for putting h -bar in the right place.
129
And the way he figured it out was from an observation called the photoelectric effect.
130
If light shines on a metal plate, that can kick electrons out of the plate.
131
One can measure this because it creates a current, so it's electric.
132
This is why it's called the photoelectric effect.
133
But for this to work, the frequency of the light must be above a certain threshold.
134
If the frequency stays below the threshold, but you increase the brightness of the light, nothing happens.
135
This was very confusing to scientists in the 19th century.
136
They could understand that it takes energy above a certain threshold to kick out an electron.
137
But if you think that light is a wave, then it's the brightness that measures this energy.
138
So why would turning up the brightness not kick out electrons?
139
Along came Einstein and he said that's because light is made of chunks of energy.
140
We now call those chunks photons.
141
To kick out an electron, the energy of the photon has to be above a threshold, not the total energy of the light.
142
The total energy of the light is the sum of the energy of all those photons.
143
But the energy in each photon is proportional to the frequency.
144
Therefore, if you want to know the total energy of the light, you take the number of photons and multiply it with their frequency,
145
and now you need a constant to convert the frequency into an energy.
146
That constant is Planck's constant, h.
147
And the h with the bar, that's called the reduced Planck's constant and is h divided by two times pi.
148
It's more commonly used in quantum mechanics because, like my uncle, it makes a lot of pi's disappear, so it's more convenient.
149
Why is it called Planck's constant and not Einstein's constant?
150
Good question, but I'll leave this for another video.
151
Let's instead step back here and ask what all this means now.
152
We've seen that what's seemingly so weird about the uncertainty principle, that there are two quantities that you can't measure precisely at the same time,
153
has really nothing to do with quantum mechanics.
154
It's just a property of waves.
155
What quantum mechanics does for you is to make this a property of particles.
156
And for that to work, you have to relate time with energy and space with momentum.
157
If you're uncertain about any of this, then you're doing it right.
158
We have also seen that the uncertainty principle doesn't mean you can't measure those quantities precisely in one round of an experiment,
159
but that means if you repeat the experiment you get a large statistical distribution for at least one of those quantities.
160
But then couldn't it be that the quantum particle actually had this property before it was measured, you just didn't know what it was?
161
Rather than doing this weird thing where it's in several states at the same time until you look at it
162
and poof it decides on one?
163
Yes indeed.
164
That's what is called a hidden variables model, and it's how Einstein thought quantum mechanics really works.
165
He didn't like spooky action at a distance, and he was certain about his principles.
166
Watching YouTube videos is great, especially if they're about such fun topics as quantum mechanics.
167
But if you want to really understand the topic, then you have to actively engage with the material.
168
A great place to do that is Brilliant, who have been sponsoring this video.
169
On Brilliant, you find courses on a large variety of subjects in science and mathematics.
170
The great thing about their courses is that they're all interactive with visualizations and follow -up questions, so you can check your understanding right away.
171
This is why I like to look things up on Brilliant.
172
It's fast, it's easy, and it tells me what I need to know.
173
And they are constantly expanding their content.
174
To understand better what I talked about in this video, check out for example my course about quantum mechanics.
175
It gives you an introduction to interference, superpositions and entanglement, and of course the uncertainty principle.
176
It begins from the very basics so you don't need to bring any background knowledge.
177
And after that, you can continue maybe with their course on quantum objects or quantum computing or wherever your curiosity drives you.
178
If you're interested in trying Brilliant out, use our link brilliant .org slash sabine
179
and sign up for a free trial where you'll get to try out everything Brilliant has to offer for a whole week.
180
The first 200 subscribers using this link will also get 20 % off the annual premium subscription.
181
Thanks for watching.
182
See you next week.
📺 Stesso Canale
C16
Superfluid Dark Matter
IELTS PrepTOEFL PrepUniversity Students
C1The End of Human Mathematics? AI's Recent Breakthrough -- And What's Next
Business EnglishUniversity StudentsWorking Adults
C14
Make AI Believe in God to Keep Humans Safe, Scientist Argues
IELTS PrepTOEFL PrepUniversity Students
C1Has quantum mechanics proved that reality does not exist?
IELTS PrepTOEFL PrepUniversity Students
C13
FINALLY: A Proof that Particles Take All Paths At Once?
IELTS PrepTOEFL PrepUniversity Students
C1Mathematician Collapses All Functions to One Weird Formula
Business EnglishUniversity StudentsWorking Adults
C13
AI Will End Philosophy, Physicist Claims
IELTS PrepTOEFL PrepUniversity Students
C1We Can Now Simulate a Human Brain, Scientists Show
IELTS PrepTOEFL PrepUniversity Students
C19
Does God exist? Science does not have an answer.
IELTS PrepTOEFL PrepUniversity Students
C15
What is time?
IELTS PrepTOEFL PrepUniversity Students
C1Our Solar System Lost Two Planets!
IELTS PrepTOEFL PrepUniversity Students
C1I was SO wrong about quantum computing.
IELTS PrepBusiness EnglishUniversity Students
✨ Video consigliato
C11
623 frasi
How evolution works, in 54 minutes | Sean B. Carroll: Full Interview
IELTS PrepTOEFL PrepUniversity Students
C167
66 frasi
What science can’t answer, according to physicist Jim Al-Khalili | Big Think
IELTS PrepTOEFL PrepUniversity Students
C13
37 frasi
The Megatsunami That Struck the Entire Planet
IELTS PrepTOEFL PrepUniversity Students
C14
39 frasi
Why Walls STOP Light Waves But Not Radio Waves?
IELTS PrepTOEFL PrepUniversity Students
C1552 frasi
The Professor Who Taught People How To Think (1962)
IELTS PrepTOEFL PrepUniversity Students
C16
224 frasi
Why Does Time Stop at the SPEED OF LIGHT? Feynman's Mind-Blowing Truth
IELTS PrepTOEFL PrepUniversity Students
C12
148 frasi
If You Don't Understand Quantum Physics, Try This!
British AccentIELTS PrepTOEFL PrepUniversity Students
C1114
14 frasi
Arguments for God: The Fine Tuning Argument
British AccentIELTS PrepTOEFL PrepUniversity Students
C11
97 frasi
Pragmatics: Crash Course Linguistics #6
IELTS PrepTOEFL PrepUniversity Students
C13
404 frasi
We're 99.9% sure this pattern is true, but no one can prove it
IELTS PrepTOEFL PrepUniversity Students
Vocabolario e note di pronuncia per questa lezione
Questo video contiene 182 frasi e 2366 parole da ripetere con lo shadowing. Il parlato dura 14:44. Chi parla ha un ritmo naturale di circa 161 parole al minuto, vicino a una conversazione quotidiana. Solo il 81% delle parole rientra nelle 3.000 più comuni dell’inglese, quindi il lessico è impegnativo.
Vocaboli chiave di questo video
15 parole del video che vale la pena imparare, con pronuncia e significato:
| Parola | Pronuncia | Significato |
|---|---|---|
| frequency sostantivo | /ˈfɹiːkwənsi/ | frequenza |
| uncertainty sostantivo | /ʌnˈsɜːtənti/ | incertezza |
| particle sostantivo | /ˈpɑɹtək(ə)l/ | granello, pezzetto |
| principle sostantivo | /ˈpɹɪn.sɪ.pəl/ | principio |
| mechanic sostantivo | /mɪˈkænɪk/ | meccanico, meccanica |
| momentum sostantivo | /ˌmə(ʊ)ˈmɛntəm/ | quantità di moto |
| spectrum sostantivo | /ˈspɛktɹəm/ | spettro |
| electron sostantivo | /ɪˈlɛk.tɹɑn/ | elettrone |
| precisely avverbio | /pɹɪˈsaɪs.li/ | precisamente, esattamente |
| quantity sostantivo | /ˈkwɑn(t)ɪti/ | grandezza, quantità |
| threshold sostantivo | /ˈθɹɛʃ(h)oʊld/ | soglia |
| interference sostantivo | /ˌɪntəɹˈfɪɹɪns/ | intromissione |
| packet sostantivo | /ˈpæk.ɪt/ | pacchetto, pacco |
| experiment sostantivo | /ɪkˈspɛɹ.ə.mənt/ | esperimento |
| interfere verbo | /ˌɪn.tɚˈfɪɚ/ | impicciarsi |
I phrasal verb che sentirai
| Parola | Pronuncia | Significato |
|---|---|---|
| kick out verbo | cacciare via in malo modo | |
| go through verbo | attraversare | |
| add up verbo | sommarsi | |
| fall down verbo | /fɔl ˈdaʊn/ | cadere |
| get off verbo | scendere | |
| pop up verbo | spuntare, saltare fuori | |
| try out verbo | saggiare, collaudare | |
| turn up verbo | presentarsi, apparire |
Pronuncia a cui fare attenzione
Chi parla usa 51 contrazioni e forme ridotte, come can't, don't, isn't. Pronunciale nella forma breve, così come le senti.
- I suoni “th”: threshold /ˈθɹɛʃ(h)oʊld/, mathematics /mæθ(.ə)ˈmæt.ɪks/, mathematical /ˌmæθ(.ə)ˈmæt.ɪ.kəl/, wavelength /ˈweɪvˌlɛŋ(k)θ/, theorist /ˈθiːəɹəst/
- I suoni “sh” e “zh”: threshold /ˈθɹɛʃ(h)oʊld/, transformation /ˌtɹæns.fɔɹˈmeɪ.ʃən/, relation /ɹɪˈleɪʃ(ə)n/, flash /flæʃ/, shine /ʃaɪn/
- Parole lunghe — attenzione all’accento: uncertainty /ʌnˈsɜːtənti/, momentum /ˌmə(ʊ)ˈmɛntəm/, interference /ˌɪntəɹˈfɪɹɪns/, experiment /ɪkˈspɛɹ.ə.mənt/, transformation /ˌtɹæns.fɔɹˈmeɪ.ʃən/
Come esercitarsi con questo video
- Ascolta tutto il video una volta senza parlare e annota le parole che non conosci.
- Inizia a velocità 0,75×, fai shadowing frase per frase e torna alla velocità normale quando diventa facile.
- Registrati e confronta con l’originale, facendo attenzione a parole come frequency, uncertainty, particle.
La grammatica di questo video
Le strutture che chi parla usa di più, con le parole esatte del video:
| Struttura | Nel video |
|---|---|
| Forma passiva be + participio passato — conta ciò che accade, non chi lo fa | can't be determined · is usually denoted · is marked |
| Present perfect have/has + participio passato — un’azione passata che conta ancora adesso | you've pinned · We've seen · have also seen |
Cos'è la tecnica dello Shadowing?
Shadowing è una tecnica di apprendimento delle lingue supportata da studi scientifici, originariamente sviluppata per la formazione dei traduttori professionisti e resa popolare dal poliglotta Dr. Alexander Arguelles. Il metodo è semplice ma potente: ascolti un audio in inglese di madrelingua e lo ripeti immediatamente ad alta voce — come un'ombra che segue il parlante con un ritardo di solo 1–2 secondi. A differenza dell'ascolto passivo o degli esercizi di grammatica, lo shadowing costringe il tuo cervello e i muscoli della bocca a elaborare e riprodurre simultaneamente i modelli di discorso reale. La ricerca dimostra che migliora significativamente la precisione della pronuncia, l'intonazione, il ritmo, il discorso connesso, la comprensione dell'ascolto e la fluidità del parlato — rendendolo uno dei metodi più efficaci per la preparazione alla prova di speaking dell'IELTS e per la comunicazione reale in inglese.