You Use Quantum Physics to Smell
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You Use Quantum Physics to Smell

Our nose uses quantum physics to smell at
least according to our best theory of how smell works. Now how our noses work was always a bit of
a mystery to be but I recently learned how they worked and so I thought I would make
a video about it. When you sniff, odour molecules get sucked
into your nose and then get captured by a layer of mucus, and are then taken to a postage
stamp sized area in the top of your nasal cavity called the olfactory epithelium. This contains bundles of neurons containing
special receptor sites which detect the molecules and send signals to the brain. It has been difficult to know exactly how
receptors work because nobody has worked out a way of looking at them while they are in
a living nose. You can take them out of a nose and look at
them, but they loose their structure when they are not supported by the cell membrane
that they sit in, it would be like taking a jellyfish out of the sea which just collapses
into a mush. We know that the sensation of smell is caused
by odour molecules being caught by the receptor sites which causes those neurons to fire. But, because we can’t directly look at the
receptors, we have to infer how they work from indirect evidence. Now there’s two main theories about how
smell receptors work: shape and vibration. The shape theory says that the smell receptors
have specific shapes that fit the odour molecules, kind of like a key fitting into a lock. However this theory doesn’t quite work because
we know that we don’t have one kind of receptor for every type of odour molecule. We have about 300 different kinds of receptors,
but we can detect about 10,000 different smells, so there is something more complicated going
on. The latest theory is that each receptor is
built to fit just one section of a molecule, so any molecule that has that part has a similar
smell, so any molecule that has a sulphur hydrogen bond will smell like rotten eggs. This matches with the evidence because you
can get many different shaped molecules that end up having the same smell because they
have got a similar molecular group. However this theory can’t explain everything. There’s certain molecules that are made
of the exact same groups but are just arranged in a different way, but they smell very different
to each other. For example, vanillin, which smells like vanilla,
has all the same molecular groups just in a different order to isovanillin, which has
a very nasty sickly medicinal smell. So there is an alternative theory of smell
receptors, the vibration theory. In the vibration model of smell, the smell
receptor can tell the difference between different molecules based on how they vibrate. Each chemical bond has a certain resonant
frequency that it naturally vibrates at. Kind of like how an open guitar string always
resonates at the same frequency and so always gives you the same pitch. So different molecules have a different signature
set of vibrational frequencies which depend on what atoms they are made from and how they
are all connected. In the past, scientists have harnessed this
property to figure out the chemical composition of molecules using light, in a process called
Raman spectroscopy. When you shine laser light through a bunch
of molecules some of the light is absorbed to make these molecular bonds vibrate, and
then light with different energy, and hence, a different frequency is emitted. You can then look at the frequencies of this
new light, which we see as their colour, and work out what the molecules are made of. And it’s worth mentioning that when it comes
to light each specific colour relates a specific frequency which has a specific energy, there
is a one to one to one mapping between them. This has been a great way to detect different
kinds of molecule, so perhaps our smell receptors are doing something like this. But for many years the vibration theory of
smell was not very popular because there is no way our noses can do Raman spectroscopy
as, unfortunately, our noses don’t emit lasers beams, and we can’t be using natural
light because we can smell in the dark. But there is another method to detect the
vibrations of molecules that uses electrons instead of light which comes from the realm
of quantum physics. It’s a form of quantum tunnelling. Quantum tunnelling is the phenomena where
quantum particles like electrons can travel to places that normal ‘classical’ particles
can’t. They can jump through walls by disappearing
from one side and immediately appearing on the other. This is one of the counter intuitive behaviours
of quantum particles and is a consequence of quantum particles behaving as spread out
waves. In a specific situation electron tunnelling
can actually be used to find the resonant frequencies of molecules. If we take two metals and separate them by
a small barrier and then apply a voltage to make an electron get pushed to one side. Normally in classical physics the electron
can’t get across this barrier, but if the gap is very small it can quantum tunnel to
the other side. But there is an additional condition. An electron in a metal has a certain energy,
and it can only tunnel to the other side if there is an empty hole which has got the same
energy. But if the hole on the other side is at a
lower energy the electron can’t tunnel because there is no where for the spare energy to
go. But if we introduce a molecule into the gap
something interesting happens. If the energy difference between the electron
and the hole is just the same as the energy needed to vibrate one of the resonances of
the molecule, then the electron is allowed to tunnel across, and it drops its extra energy
into vibrating the molecule when it goes across. Scientists have built machines that use this
property to probe molecules, the technique is called inelastic electron tunnelling spectroscopy. You can put in different molecules, change
the energy difference between the electron and the hole and see where the electron tunnels,
which tells you about the resonances of the molecule and so tells you what it’s made
from. So perhaps our nose is doing the same thing. Perhaps our smell receptors are behaving like
that metal and the gap, which is waiting for an odour molecule to come in, which allows
an electron to pass across the receptor and trigger the nerve. To find out scientists did some very clever
experiments. This theory makes a very specific prediction,
that the odour of a molecule depends on the frequencies it vibrates at. So if you could change the frequencies of
a molecule you’d also change it’s smell. So that’s exactly what they did. They took a molecule, but replaced all of
the hydrogen atoms with a heavier from of hydrogen, called deuterium, which instead
of just having one proton in the nucleus the’ve got a proton and a neutron. Deuterium has all the same chemical properties
as hydrogen, but is much heavier. The scientists got a bunch of the normal molecules,
and the heavier ‘duterated’ molecules and got different subjects to sniff them to
see if they could tell the difference, humans, fruit flies and white fish. They found strong evidence from these creatures
that these two different forms of the molecule actually smelled different! This is really cool because it is really good
evidence that our noses use quantum physics to smell the world, which I find utterly amazing! Quantum physics shouldn’t play much of a
role in our warm complicated bodies, so it’s crazy that it does. But as successful as the vibration model is,
it can’t explain everything. You may have heard of chiral molecules which
are molecules that are made of all the same stuff but arranged as mirror images of each
other. For example carvone has a left handed and
right handed form. Because these are made of the same atoms and
bonds they have all the same vibrations, so will look identical to vibration tests like
Raman spectroscopy and inelastic electron tunnelling. So according to the vibration theory they
should smell the same, but they don’t. One form smells like caraway or dill and the
other smells like spearmint. So what can we conclude from all of this? It seems like you need both the shape model
and the vibration model to explain how we smell. Perhaps our receptors first check the shape
of the molecules, and then if they get past that barrier they are checked for their resonance
vibrations through quantum tunnelling. But we won’t know exactly how this works
until we can figure our a way of directly observing the receptor sites in action. But isn’t it crazy to think that these experiences
of smell we have of a flower, or coffee or freshly baked bread, or a newborn baby, this
experience of the world came to your brain through something as strange as quantum tunnelling. So quantum physics which seems for many people
to be so strange and abstract, well, its going on right up your nose. Just like all my other videos I’ve made
a poster for this one you can either buy it or get it for free, check in the description
to see where to get those. Also, um, if I have made any mistakes in this
video, which does happen I have put that in the description too, so if you spot anything
check there and if it is not there then leave a comment and I’ll address that. Other than that, I’m going to be making
a tonne more videos now under the banner of Domain of Science so I’ll see you on the
next one.

100 thoughts on “You Use Quantum Physics to Smell

  1. If you don't know why you are subscribed to this channel, I just changed the channel name from DominicWalliman, so you probably subscribed after my Map of Physics or Map of Mathematics videos. Even though I changed the name, everything else is the same, and I'll be doing more of the same kind of videos! Sorry for any confusion.

  2. Happens that nature doesn't differences between quantum and regular physics, they are all physics, so electrotunneling is just another tool, just as sound listening, doesn't gets labeled as quantum or not by nature

  3. Hello I have one question for you Domain of Science. Why when I smell the fragrance of perfumes. Or gas. Plastic. And other. And why the scents create me Nausea and vomit. Explain to me what doctor can help me

  4. Does that mean if we combine inelastic electron tunneling spectroscopy with partice-shaped holes,we could create an artificial nose for our future robots?

  5. I don't find this fact of quantum smelling as interesting as evolution, which can explain why life can develop anything that uses the laws of nature to its survival benefit.

  6. "Odor molecules,"?!? Do you mean free floating molecular discharge radiating from most all material structures….. Or are there dedicated molecules of odor loitering around things?

  7. Hi @Domain of Science mybe you can answer my questions

    Does the resonant frequency of molecules change when we increase the temperature?

    I have read a lot about thermodynamics lately and on most forums people write "if we increase the temperature of a substance, the frequency of vibration increases"… but what I have found in a few scientific papers is "actually its the amplitude of atomic vibrations which gets stronger if we increase the temperature of a substance and the frequency stays constant". The second quote would make more sense to me if I look at potential energy curves of molecules… what do you think?

    So basically an IR-Spectrum of a substance must be the same at different temperatures right?
    My second thought was: if I have an Infrared Laser of a specific wavelength and theres a substance which absorbs exactly that wavelength of light, its temperature raises as the atoms begin to vibrate more vigorously… but the stronger vibrating molecules still keep absorbing that light and get hotter and hotter, so the vibrational frequency must stay constant right?

    Thanks so much, it would be a big help

  8. Great video! Can't the fact that the proteins that participate in quantum tunneling are chiral account for the different smells of enantiomers? Like having a chiral Raman spectrophotometer?

  9. hallo i found your excellent channel a few weeks ago. i'm following your creations about 3/4 times a week. but unfortunately my english is bad and the only traslation i find is the "simulataneous" in ht e options of subtitles. it's not very good. do you think you can incude italian subtitles for all videos in the future? i hope yes. i wish and i hope to show your works to kids and children an discuss about with them so, a good translation should be very useful. thank you, bye, Antonio.

  10. My theory is : Nose is using external light to vibrate the molecules, even in dark, because we are never into "absolute darkness" there are always a few photons roaming around, even on the vast darkest places on universe

  11. What about the sense of smell in other animals? Do the same theories apply, or are there different ways of smelling? Maybe it would be easier to investigate how receptors work in some animal noses rather than in humans?

  12. Molecular vibration is not smell. Smell is Venus Flytrap style of many receptors in combination. No vibration needed.

  13. Hi,
    The answer to the shape/vibration/chirality problem is birefringence. The polarized light contains spin information. Problem solved.

  14. Did you make this video after compiling research papers or read it from a book? Read the book "The Life on the Edge" by Jim Al Khalili which talks about more such amazing phenomena.

  15. I love your videos and the posters are so good! Never did I have a clearer picture (quite literally) of all kinds of sciences. This is amazing, thank you so much for divulging knowledge to those who are not experts in this field, great work.

  16. This theory I developed based on differentiation may provide some pointers to explaining the inexplicable aspects of olfracation. Although perhaps a bit sucky, it perhaps deserves some merit (it's only a theory):

  17. You said, "Our nose uses…". This is incorrect: we don't all share one nose. Regarding carvone: when does carvone not smell like carvone? Answer: Obvious! When it doesn't smell like carvone! (Do you understand what I am saying?) No doubt, outside observation helps us DIFFERENTIATE the wood from the trees; and see farther, as Newton is famously quoted: if you view all known existence (infinite earths; infinite universes etc.) as one unit, then that is always a good place to start.

  18. I like that this has quantum tunneling involved in not just human, but many animal's ability to smell. It shows that these organisms seem to use the same molecular apparatus to identify the molecules and I just think it's awesome that quantum physics takes place inside my face every time I breathe in.

    But what's even more awesome is that if this is possible here in this one example, what else could be possible through quantum technology? Other senses? There's always quantum computers, which seem to be getting on nicely. But what I find truly crazy is the potential for organisms on other planets around other stars – and what they might have done differently with such a crazy versatile tool. Then again, we're getting smarter and learning about it so I suppose it's now one of our new tools to explain things and test against – Hooray for progress!

  19. Quantum tunneling actually describes how an electron approaches the interface (at some energy) and can appear at both sides simultaneously. That is the "tunneling" effect, kind of like it is depicted in science fiction movies. Whether the particles does bleed into and through another dimension, that is yet to be debated. As of the moment, there has been a lot of computing and modelling work based on classical and quantum equations which guys like Einstein, Bohr, Schrodinger have formulated, but no one really understands this stuff. I have been working in gas sensing technology and interfaces for over a decade (Ph.D. and all) with about 50 publications.

    There also thermodynamic and magnetic components that we haven't even conceived of, let alone electron spin-up or spin-down. It becomes very very complicated to model, however for simplicity, 'the nose works'. We have yet to really scratch the surface…

  20. Meanwhile, hemeopathists and paranormal beliefs are on the rise all across the world… perfect, fucking wonderful; and such and optimistic approach to the future

  21. So how does this relate to the function of human pheromones or animal pheromones and sexual selection? How does quantum tunneling allow for "most suitable mate" determination?

  22. You talk about Raman Spec but you completely forgot to even mention IR spec, that is a legitimate and viable way we can smell, though it leaves a lot to be explained like the carvone example, the + and – forms would have the same spec. anyway, thanks for sharing

  23. I think now it's time to make a poster for the "PARTICLE PHYSICS" and in the last topic of this poster will be Higgs Boson..!😎🇮🇳

  24. But why do we do we smell the flowers . As it is in solid state how does they travel and what are molocule travell

  25. If we smell through are nose and take in molecules than according to that we can smell the whole thing until it gets smallest thing?

  26. do vanillin and iso-vanillin (@ 2:28) have different characteristic frequency ??? if not, then this case will not fit either of these theories…..
    same confusion goes with @ 7:53 for me… as its structure & frequency is identical, then how can we differentiate it using shape theory either 🤔🙄

  27. Are there odors which human can’t smell but other species can as you hypothesized the smell as an spectrum like the light UV & IR could we have invisible scents

  28. Wonderful. Amazing. Our sense of smell is nothing compared to that of dogs 🐕! You mean, if we, the supposedly great species with the largest brain, use "quantum physics" to smell, what do amazing dogs use? They 🐶 can smell cancer in a human breast! What's beyond "inelastic electron tunneling spectroscopy"? 😁

  29. This is amazing and so well vulgarized. While I am a neuroscientist, I am far from having a good understanding of physics. You have helped me in this respect so thanks. So, I have an "out-there" question. Can humans detect smells that arise from basic human emotions, specifically fear and could we measure it. Ex: expose a participant to stimuli that induce a fear response while wearing a simple cotton t-shirt. take another blind subject and expose them to the odour and ask what emotion they think the person wearing the shirt was feeling. I know this sounds crazy but I do have a rationale behind it.

  30. Would it be similar to the way we see, then? I have this idea that the world as we percieve it, is our brain's interpretation of vibrations. Everything in the universe vibrates and our brain translates it as "colour", "smell", "taste", "heat", etc. Is that right? (thank you for the video)

  31. “Retronasal Olfaction” by Dr. Linda Bartoshuk of University of Florida.

    Is this theory is true?

    I think this theory is not true. I tried to test this theory by my body. But I never could realize tracing experiment of this method.

    1) This theory says the “smell air” from food in the “mouth cavity” goes to “throat” and go UP to “nasal cavity” and go out “outside air”. This “smell air” gives stimulation to “odor sensors” in “nasal cavity” and “signal” reaches to “cranial nerves” and feel “smell”.

    Is this true? I could not. “Retronasal Olfaction” effect. This theory shows “smell air flow” at following drawing. I add “circle” at “air turn” point. I could not control this turn in my body. Try and make sure you can lead your “smell air” from food in the “mouth cavity” goes to “throat” and go UP to “nasal cavity” and go out “outside air”

    I list up wrong points of this theory.

    1) “Smell air” go UP to “nasal cavity” DIRECTRY? This is wrong. “Smell air” go DOWN to “lung”.

    2) Two both motions of “smell air” goes UP and moves to “nasal cavity” cannot do it at continuous activity. These motions needs separate activity through “lung” with one pause.

    I can show “truth” by my body experiment.

    1) “Smell air” went DOWN to “lung” and after “one pause”, I kept out the “mixed air” of “smell air” and with existing air in lung. “Smell air” became diluted.

    2) “Orthonasal Olfaction” can feel DIRECTRY from food at outside mouse. This is strongest smelling.

    3) Once entered “lung smell” from “in mouth food” go up to “nasal cavity” is smallest smelling with mixed air.

    You can imagine this activity is “tobacco smoking”. “Smoke with nicotine drug arousal” enters “from closed lip” to “mouth cavity”. This “smoke” flows DOWN to “lung”. This “addiction nicotine smoke” is absorbed into “lung blood vessel”. “Blood” delivers “Nicotine” to “brain”. “Nicotine” makes balance of “brain record” and erases “nicotine hunger”. One hour later “nicotine rate” in “blood” go down. “Brain record” asks smoking to make balance of “nicotine” in the “blood”.

    “Smoke” that did not absorbed in the “lung” go UP to “nasal cavity”. This “smoke” gives stimulation to “odor sensors” in “nasal cavity” and “signal” reaches to “cranial nerves” and feel “smell”. This is same action to feel smell from “food” in “mouse cavity”. To feel “smell” from “food” in “mouse cavity”. It needs 2 steps motions. 2nd motion from “lung” needs “lung breathing” and needs to close the “lips”. “Retronasal Olfaction” is the “fictitiousness”.

    Toshinaga Urabe

    [email protected]

  32. Imagine you can transform smell into data.. how smart artificial would become. Btw I was researching on AI and this thought suddenly hit and I ended up to your videos.
    Very informative. Thanks alot

  33. Okay, so this kinda explains why my grandma ripping ass smells so putrid

    Now I need to find a video on what the hell is going on inside her that's causing this smell….

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