If You Don’t Understand Quantum Physics, Try This!

Quantum physics has a mystique of being complicated
and hard to understand, in fact Richard Feynmann who won the Nobel prize for his work on quantum
electrodynamics said: “If you think you understand quantum physics, you don’t understand
quantum physics”. Which is kind of disheartening for us because if he didn’t understand it,
what chance do the rest of us have? Fortunately this quote is a little misleading.
We do in fact understand quantum physics really well, in fact it is arguably the most successful
scientific theory out there, and has let us invent technologies like computers, digital
cameras, LED screens, lasers and nuclear power plants. And you know, you don’t really want
to build a nuclear power plant if you don’t really understand how it works. So quantum physics is the part of physics
that describes the smallest things in our Universe: molecules, atoms, subatomic particles
thing like that. Things down there don’t quite work the same way that we are used to
up here. This is fascinating because you and everything around you is made from quantum
physics, and so this is really how the whole universe is actually working. I’ve drawn these protons, neutrons and electrons
as particles, but in quantum mechanics we really describe everything as waves. By the
way I’m using quantum physics and quantum mechanics interchangeably, they are the same
thing. So instead of an electron looking like this, it should look something like this.
This is called a wave-function. But this wave-function isn’t a real physical
wave like wave on water or a sounds wave. A quantum wave is an abstract mathematical
description. To get the real world properties like position or momentum of an electron we
have to do mathematical operations on this wave-function, so for the position we take
the amplitude and square it, which for this wave would look something like this. This
gives us a thing called a probability distribution which tells us that you are more likely to
find the electron here than here, and when we actually measure where the electron is,
an electron particle pops up somewhere within this area. So with quantum physics we don’t know anything
with infinite detail, we can only predict probabilities that things will happen, and
it looks like this is a fundamental feature of the Universe which was quite a departure
from the clockwork, deterministic universe in classical physics, the kind of thing Newton
derived. This wave-function model predicts what subatomic
particles will do incredibly well, but weirdly we’ve got no idea if this wave-function is
literally real or not. No one has ever seen a quantum wave because whenever we measure
an electron all we ever see is a point like electron particle. So there is like this hidden
quantum realm where the waves exist, and then the world we can see, which is where all the
waves have turned into particles. And the barrier between these is a measurement. We
say a measurement ‘collapses’ the wave function, but we don’t actually have any
physics to describe how the wave collapses. This is a gap in our knowledge that we have
dubbed the measurement problem, and this is one of the things that Feynmann was referring
to with his quote. Another confusing thing is how exactly to
picture an electron. It seems to be a wave until you measure it, and then it is a particle,
so what actually is it? This is known as particle-wave duality, and here is an example of it in action:
the famous double slit experiment. Imagine spraying a paintball gun at a wall
with two openings in it, you’d expect to see two columns of paint go through and hit
the wall behind. But if you shrink this all down to the size of electrons you see something
quite different. You can fire one electron at a time at the slits and they appear on
the back wall, but as they build up over time you get a whole pattern of stripes, instead
of just two bands, this pattern of stripes is called an interference pattern, something
you only see with waves. The idea is that it is the electron-wave that goes through
both slits at the same time, and then the waves from each slit overlap with each other,
and where the waves add together you have a high probability of the electron popping
up at the wall, but where the waves cancel out the probability is very low. So actually
on the back wall the highest probability of finding the electron is in the middle of the
slits, and then it goes down and up again, and down and up again and this is the interference
pattern. So when you fire one electron after another they follow this probability distribution
and this interference pattern starts building up, and that’s exactly what we see in experiments.
So this shows that electrons behave like waves in this experiment. A question is what actually happens to this
spread-out electron-wave when you do a measurement? It seems like it goes from this spread out
wave to this localised particle, but like I said, there’s nothing in quantum mechanics
that tells us how the wave-function collapses. And this is not only true for electrons, but
for everything in the Universe, so this double slit experiment has huge consequences for
our model of the Universe, and it was very surprising the first time it was done. Physicists
are still grappling with this question today and have come up with many interpretations
of quantum mechanics to try an explain these results, and explain how reality actually
works. Okay lets go back to the wave-function. Now
we can use this picture to explain other features of quantum physics that you may have heard
about. So this is just one possible wave-function
for an electron, but there are many others. Like this one for instance. This says that
the electron has a probability of being over here, and a probability of being over here,
and very little probability of being in the middle. This is perfectly allowable in quantum
physics and this is where the phrase ‘things can be in two places at once’ comes from.
This is known as superposition, which comes from the fact that this wave can be made by
adding, or superimposing these two waves. The word superposition just means the adding
together of waves and we already saw this in the double slit experiment, and is not
really a very special phenomenon. You can even see superposition by dropping two pebbles
into a pond where the ripples overlap. Now for entanglement. Let’s say two electron-waves
meet. Their waves interfere with each other and become mixed up. This means that mathematically
we now have one wave-function that describes everything about both electrons and they are
inextricably linked, even if they move far away from each other. A measurement on one
of the particles, like measuring if it is spin up or down is now correlated with a measurement
on the other, even if they move billions of miles away. Einstein was very uncomfortable
with this idea because if you measure one of the particles here you instantaneously
know what the other will be even if it is billions of miles away, and that’s got a sort
of whiff of faster than light communication, which is not allowed by the theory of relativity.
But it turns out you can’t actually use this to communicate information, because the
measurements give you random results, but the fact that they are correlated means that
somehow there is a link that stretches over that distance. This is called non-locality. Quantum tunnelling. Quantum tunnelling is
where particles have a probability of moving through barriers, essentially allowing things
like electrons to pass through walls. When a wave-function meets a barrier it decays
exponentially in the barrier, but if the barrier is narrow enough the wave-function will exist
on the other side meaning there is a probability of the particle being found there when a measurement
is made. In fact the only reason you are alive is because
of quantum tunnelling in the Sun which make the Sun shine. Protons normally repel each
other, but they have a small probability of quantum tunnelling into each other which is
what turns hydrogen into helium and releases fusion energy. All life on Earth exists because
of energy from the Sun, except for life around hydrothermal vents. Now on to the Heisenberg Uncertainty principle.
I said that the beginning that this wave-function contains all of the information like position
and momentum of the electron, we just have to do some maths on it. The position is given
by the amplitude, or height of the wave, and the momentum is given by the wavelength of
the wave. But for this specific wave the position gives
us a probability distribution, so we don’t know exactly where the electron is. Also there
is an uncertainty in the momentum because this wave is made of many different wavelengths. But we can reduce that uncertainty, let’s
have a wave that only has one wavelength, so a sine wave. Now we know the momentum exactly
because the wavelength has a single value, but look at the position. There is an equal
probability of the electron being found anywhere in the universe. Okay let’s do the opposite
let’s make a wave that has only got one position. Now we know exactly where the electron
is, but what is the wavelength of the wave? Now the wavelength is very uncertain. Basically
only a sine wave gives you a precise momentum, and any wave that isn’t a perfect sine wave,
you have to build out of multiple different sine waves, and each of those multiple different
sine waves has got a different wavelength, and hence you have a range of possible different
values of momentum for the particle. This is Heisenberg’s Uncertainty principle,
you can only know certain things precisely, but not everything. Either you have got a
definite value of momentum, and don’t know anything about position, or you know the position
very well, but don’t know anything about the momentum, or you are in some intermediate
state. And this isn’t a limit of our measuring apparatus, this is a fundamental property
of the Universe! And finally, where does the name ‘quantum’
come from. Well a quanta is a packet of something like a chunk of something, and one of the
first quantum effects people saw were atomic spectra which is where atoms give off light
with specific discrete energies. It works like this. Imagine a string that is tied at
both ends, like a guitar string. If you pluck it, only certain waves can exist because the
ends are tied down, in this situation we say that the wavelengths are quantised to certain
values. The same thing happens if you ties the ends
of the string together because the waves have to match up, they can only vibrate in certain
restricted ways. And this is what is happening to an electron in an atom. The electron-wave
is constrained by the atom and quantised to certain wavelengths, short wavelength have
high energy and long wavelengths have a lower energy. This is why the light emitted by an
atom looks like a barcode because each bar of light corresponds to an electron jumping
from a wave with a high energy to one with a lower energy, and at the same time emitting
a quantised photon of light when it does this. So the light from an atom is quantised to
discrete packets of energy. Okay so that’s all the basics of quantum
physics, here are some technical notes which aren’t essential to know, but pause the
screen now if you are interested in a little more mathematical detail. So to round up. In quantum physics objects
are described with wave-functions, but when we measure them, what we see are particles,
so this leads to particle-wave duality, and also the measurement problem. And the consequence
of these wave-functions are the quantum phenomena of superposition, entanglement, quantum tunnelling,
the Heisenberg uncertainty principle and energy quantisation. So if you understand these things
you have got a good basic understanding of quantum physics. Despite its reputation I think quantum mechanics
isn’t too difficult for most people to get the basics of what is going on. In the past
I have relied upon analogies to try an explain it, but here I have just described what is
actually going on which I think might be more helpful. But if you have more questions I’ll
be on the comments below so ask away. For me the weird thing about quantum physics
is that on the one hand it is incredibly accurate and predictive but also it has got giant holes
in it like the measurement problem which we just don’t understand. So we can wonder,
will we ever actually understand quantum physics, or is it just too abstract for our human brains
to comprehend. Well I hope this video has helped you understand a little more about
how quantum physics works. And thanks to the sponsor of this video brillaint.org,
who have just launched their daily problems which you can dip into if you have a spare
5 minutes each day. Each problem teaches you some interesting facts that you can then use
to solve the problem. And if you enjoy that specific problem there are links to more on
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if you are confused and need more guidance, then you can join with the community discussions.
So this is a simple, fun way to keep learning more. If that sounds interesting go to brilliant
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do so will get 20% off the annual subscription which unlocks all of their premium content. Well that’s it from me, thanks for watching
and I’ll see you next time.

100 thoughts on “If You Don’t Understand Quantum Physics, Try This!”

  1. Amazing video. At last I understand so much more about superposition, uncertainty principal and so much more. Thanks.

    Can you help here please: I bought a book "How Schrödinger's cat escaped the box" by Peter Rowlands. I feel OK until he starts talking about quaternions. I managed to ask him, over a cup of coffee, to help me understand. As a typical lecturer he gave me more to think about. His friend said I could use coloured counters to understand this. Can you help please? I know quaternions are used in game programming rather than using complex matricies, and you don't get gymbal lock but I don't know much more.

    Please, Please, PLEASE do a video based on the chapters in his book. I have seen other youtube videos but your videos make great sense as you put a lot of work into explainig complex concepts in a simple way.

  2. Let there be lie. Quantum anything is BS. All these fifty years of conscious brooding have brought me no nearer to the answer to the question, “What are light quanta?” Nowadays every Tom, Dick, and Harry thinks he knows it, but he is mistaken. – Einstein

  3. I’m in 10th grade and I under stood only the following
    Sub atomic particles
    Adding ( super position)
    theory of relativity
    That’s pretty much it

  4. What you know! you don't know? Like the back of your frenemies hand. If Quantum Physics were used it could have invented computers, digital cameras, LEDs, lasers, and transmute lead into gold. It describes everything we don't know because we don't know if it can. Large physics is of-course not the same as small physics because it's little but big at the same time. 1:46 Take a waveform and square it; changes AC into pulse DC so absolutely it's between 0 and 1 no negativity here. So it explains nothing so we should know everything when we apply what we don't know.

    OK! For those looking for what the Hello their talking about! 3:16 An experiment with double slits was used to examine particles when the beam goes through the slits it produces a pattern that is the same as a wave going through the slits. To explain THIS experiment quantum people believe that particles are wave too. They have no answer to why it happens. So they CREATED quantum physics which is a JUNK science. One particle is impossible to emit or see in the experiment. Two particle react to each other – same types repel. The position between particles is uncontrollable; so how can a whole new science be created from stupidity – quantum magic. 9:32 Again the slit experiment. "Spectrum of light" absorption by an atom, is not quantum physics. He states gives off light which is wrong (atoms can only reflect what they are given). Have a great life and keep thinking or not. SCHRODINGER cat is always dead when I look into the box.

  5. All this physics stuff is really interesting man I wish I would have been paying more attention in school cuz now I'm interested in it I want to know but I guess I'm too old to learn this stuff is really intriguing but I don't understand a word of what you saying I keep trying though

  6. Need a scientific study on the science of the uncertainties of science .. New creative scientific terminologies are welcome . 👍👍

  7. Entanglement to me means one of many methods by which all of Gods creation have a record of their movements etc in another realm
    There is an eternal book which has measured all acts of all that exists in a mathematical form
    If these particles can be manipulated in another universe then to me this explains why everything has form nd when something dies it's stops collaborating atoms become dispersed which to me means the opposite particle has been deactivated thus both cease?
    Nd if their is a day of judgement where it is claimed by many that all the children of Adam will be recreated nd go through judgement for their time on earth etc.. now people ridicule the dead coming back to life nd that life is a grand scheme from a Creator
    Could entanglement theory solve this idea?
    Or am I way out there?

  8. Give your life to Jesus Christ. Believe and Pray: God, I know that I am a sinner and unless you save me I will be lost forever. I believe that Jesus Christ is the true Son of God, died on the cross for my sins and arose on the 3rd day. I accept Jesus as my Lord and Savior, in the name of Jesus, Amen.

  9. Thanks! I now know less about the subject than before. I made it through about 5 minutes before before deciding I made it this far in life without understanding it and am satisfied that I will continue the rest of my life just fine still not understanding it.

  10. Consider this: The people now tasked with grappling with the most important and complex theories to steer humanity in the right direction are the same people we would all be spitting chewed up paper at, blowpipe style through snapped pens.

  11. His quote is actually ACCURATE. If you understand it then you don’t understand it. Cuz there’s nothing to understand. Its beyond us.

  12. Thanks.I cannot honestly say I have understood but something is cooking..
    Quantise what another beautiful word.

  13. You didn’t mention how when the slit the electron goes through is measured, you no longer see an interference pattern. Is this true or just a rumor?

  14. I first thought this was Quantum Physics 101 when I first clicked on it. After 7 mins into the video, I concluded: This is Quantum Physics 10100.

  15. All videos I see about this topic aren't helpful and kinda goes to the same place.

    Time to do some experiments by myself.

    If at least I had access to a particle accelerator…

  16. If Heisenberg says you don't understand quantum physics if you think you understand it, who are you to say we do understand it? You're not as brilliant as Heisenberg. You're not a pioneer as Heisenberg was so what are you telling?

  17. Man, I watched many lectures and videos on QM and this is probably the most lucid and helpful explanation of QM. Mucho gracias. Do one on Special and General Relativity and other concepts in general relativity please!

  18. I think I know the part, nobody understands. Simply Put: when they shoot the thingies through the barrier, because of the fact, everything in the universe is vibrating or moving, and gives off positive or negative waves of repulsion or attraction, when they come into contact with each other, duh.

  19. Interestingly they took this double split experiment to another level. They invited people, one at a time, to concentrate as the particles went through the slits. When someone concentrated on them the particles produced a perfect pattern on the wall the other side. When someone wasn't concentrating on the particles the results were a random pattern. They did the experiment thousands of times always with the same result. Now, does this mean that our brains have an influence on energy? If so, then it is possible that the Law of Attraction is real and that we are capable of creating our own reality based on our thoughts because everything is made of energy, including us. Very interesting concept!

  20. I hear friend of mine talking about QM everytime and i looked like "ok what?" Kind of look…that infact made me become very inquisitive(sorry if i spelt the word wrong) and i came on your post and found so much of valuable information about QM that I never knew…I would strongly request you to do more videos in detail such as this to give general idea about many things that people dont understand! I am SUBSCRIBING TO YOUR PAGE RIGHT THIS VERY MOMENT!!!

  21. Lìstening to this guy is a bit like "and then the clock struck 13"- and it probably does in the Quantum world. Thinks one thing in one sentence, and in the very next contradicts himself. One minute it's understandable, the next it's impossible to know. Very Quantum. The absurdity of his position. You can't understand that which you CAN'T know.

  22. My Professor says it fine if we do not fully understand the Quantum Theory, but he confused me further when gave me a fail for my final exam!!

  23. Ok guys, here's the thing in a nutshell from a guy whose job is to teach the thing to youngsters : there is no absolute truth as far as humans are concerned, but try and devise precise cristal balls called sciences that fit, and describe, the observable physical world. So, don't try and make it what it is not, a religion. If you want absolute, go see a priest, Imam, guru or Rabbi.

  24. Me thinks you scientific types have made it too complicated and invented terms and math to try and fit into your idea of what's happening. If what you are saying about electrons being random then crt televisions wouldn't work.

  25. Amazing video overall, explaining complex ideas in a compact and understable way. My only criticism is the ending: "will we ever actually understand quantum physics, or is it just too abstract for our human brains to comprehend." Quantum physics, as all scientific theories are, is based on experimental observation, and the limit to theories generally comes from the lack of experimental data to draw conclusions from. It's not a conceptual issue, it's not that quantum mechanics is just too much for our brains to understand.

    That's not to say that science never goes against intuition, it often does, our subjective experience of reality generally revolves around non-relativistic big things. Other factors like relativity and quantum mechanics come into play when we stray too far from this small band we call everyday life, but that doesn't mean we can't gain new intuition about these things. Humans are flexible like that.

  26. this makes me feel so dumb. i just started chemistry (you know that means messing with metric system) and found that 0 degrees kelvin is impossible (physically) to reach because quantum mechanics are evolved and its confusing for most scientists, and now i feel like im soooo behind and that if like 15 year olds now are doing this, and other harder math and English and science and stuff and im at the regular basics, how am i ever gonna get into a good school like Howard, or NYU or Georgia tech. let alone multiple schools. im a JR in high school and this is all making me scared. its almost depressing to me… i could really use a boost in drive because i feel so hopeless rn (no im not going to kill myself, im just confused on what i should do, and i have like all the qualities of the bad characteristics infinity stones laziness, unfocused(easily sidetracked), distracted, not a hard worker. i want to be all the things im not and i knowledge my weaknesses but im so overwhelmed… i just went to off track about what i was originally talking about (quantum mechanics) anyways if someone could at least tell me something to raise my spirits. im not looking for pity i just really need help and im not really in the best position to talk to any of my "family"

  27. You are here and you are also there, the world is in you and you are in the world, you don't travel in time, you are time and distance itself, moving forward backward up down and around by not moving at all….

  28. Quantum mechanics is well understood but I'm afraid I don't think that understanding is conveyed here* and there are errors: 1) The familiar classical sort of correlation – "Bertlmann's socks" – rather than quantum correlation (entanglement) is described (see also https://arxiv.org/abs/1809.01751 ). 2) The "measurement problem" is interpretation-dependent and only a genuine problem for those interpretations that do attribute some degree of reality to the state (see e.g. https://www.mdpi.com/1099-4300/17/11/7374/htm ).

    Edit: More on error 1)… "Take any explanation of Bell inequalities or quantum non-locality [entanglement], and substitute ping pong balls for every quantum particle in the account. Then, if what the author is selling as paradoxical still remains true, he/she isn’t telling you anything about quantum mechanics after all." https://arxiv.org/abs/quant-ph/0107093

     * One might start by explaining, e.g. by describing the form of multiparticle states or by drawing on arguments contained in Schrodinger's "cat paper" (https://www.jstor.org/stable/986572 ) , exactly why, irrespective of preferred interpretation, one can't think of the quantum state – the "wave function" – in naively realistic ways; as representing the electron or whatever. Ideally though, one would start with the modern developments in (and understanding of) probability theory which lead directly to the conclusion that it's fair to say that QM is well understood these days https://twitter.com/SchreiberUrs/status/1154074907325718528 (see also: http://blogs.discovermagazine.com/cosmicvariance/files/2011/11/banks-qmblog.pdf and https://arxiv.org/abs/math-ph/0002049 ).

  29. Не частица ведёт себя как волна, а пространство приобретает волновую функцию при взаимодействии с частицами и в горизонтальной и в вертикальной плоскостях. Другими словами волна, это форма взаимодействия частиц и пространства. И абсолютно не имеет значения атомы это или вакуум. Если вы не изучили свойства пространства, то не нужно рассказывать сказки про какое-то мифическое поведение частиц. Да. Взаимодействие частиц и пространства разумно. Но давайте без мистицизма, иначе это уже не наука получается, а псевдонаучный бред. Любое движение частиц в пространстве зависит от свойств пространства. Вот почему вы не говорите о том, что вакуум практически ничем от атомов не отличается. Вот это вопрос. Не хотите опозорить нобелевский комитет за то, что они раздают премии налево и направо?

  30. I'm truly shocked…..
    WHAT??? U say I'm just a wave ??? Or the waves out there are particles ????
    Ok whatever it is, I'm glad GTA 5 exists

  31. Pentagon Wave Corporation, we apply Quantum physics through experiences with humans to reach a higher conscious level in a fast way. Now delivering ENQUIRY in Colombia.

  32. What i understand is that everything in the universe is at every location and so is time. The PAST, THE PRESENT AND FUTURE ARE JUST OUR way of explaining events. Time is an abstract entity . There is only ONE time. There is only ONE of everything. Zero and infinity are concepts. Both are SAME.
    Wish you a happy UNITY.

  33. All of the Google search philosophers are out talking about something they honestly do not comprehend. Literally no one believes that you are an authority on this subject. So get off your high horse, no one is impressed.Actually, it is rather cringeworthy.

    The comment section is suddenly filled with experts. Yeet!

  34. This is false on so many level. You don't need to be a Quantum Physicist to know that a probability distribution is the integration of a probability density over a domain. With regards to the probabilistic position of an electronic wave function over, say the line, this has nothing to do with the amplitude square as this is a defined number for a wave vibrating at that particular frequency.

  35. Everything is a wave. Even us. When we cry our emotions are so strong that it literally creates a wave.. WATER. Same goes when we are happy. What about during SEX? Like they say its the motion of the ocean, pretty much the wave you create and when you feel it strong enough ahhh creates another liquid. This is why girls squirt and why sometimes they feel orgasms in waves. When you look at something all that happens is the light wave is seen by your eyes and that same wave flows through your brain and creates a thought that thought.

  36. Quantum processor is basicly a computer that can know what the outcome of a single particle such as molecule or protons if combined with its own algorithm
    And throughout this discovery we can debunk everything in the universe

  37. I just remember my chem professor talking about how If you did nothing but walk at a wall for eternity youd eventually phase through it.

  38. isn’t it possible everything already exists in every dimension at every vibration but only manifests in the dimension or vibration with which it is matched at any given moment?

  39. I think there is a little problem with saying everything is made from quantum physics.(00:57)
    The logical thing to say would in my opinion be: "Things around us can be explained using quantum physics"

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