- Hi, everyone, Jade here.
Today I'd like to introduce you to a new
and exciting field of research.
It's still quite speculative,
but it's growing rapidly in popularity.
It's called quantum biology
and it asks a very interesting question.
Are there biological processes
which need quantum mechanics to work?
Now, this question is surprising for a couple of reasons.
Quantum processes generally need
very specific conditions to work.
When physicists explore quantum effects,
they work in pristine conditions,
usually at temperatures of near absolute zero
with very expensive equipment in complete isolation.
So it seems odd that these same processes take place
in the hot, wet, messy world of life.
But experiments over the past decade
have shown mounting evidence that this is in fact the case.
Quantum biology is also interesting
because it brings together physicists and biologists.
A friend of mine, Pat Kelly,
who runs the biology channel called Corporis,
actually came to me with this idea.
Together we've crafted a three part mini series
which explores different instances of quantum biology.
This first episode is about how plants
may use quantum mechanics
to perform perhaps the most important
biological process on earth, photosynthesis.
On Pat's channel,
we talk about how the engines that run our bodies, enzymes,
may use a process called quantum tunneling.
And finally, in the third episode,
we talk about my favorite phenomenon,
how some birds may use quantum entanglement
to navigate the globe.
So then, let's get started.
How some plants may use quantum mechanics.
The story starts in April, 2007,
where a group of MIT physicists
were sharing science articles they'd found that week.
One of the articles was suggesting
that plants were mini quantum computers.
The group exploded into laughter.
The world's brightest minds
had been trying to create a quantum computer for decades,
and now it was being suggested
that some dumb plant had outsmarted them?
But as we'll soon see, they were foolish to laugh.
First, let's talk about
why someone would even make that claim.
Plants as quantum computers?
It does sound a bit farfetched.
Well, to understand this,
we first need to understand a very old puzzle in biology.
Why is photosynthesis so efficient?
Pat can explain this much better than I can
so I'm gonna let him handle it.
- Life on earth is only possible because of photosynthesis.
You've heard of this phenomenon before.
It's the synthesis of energy out of light or photons.
Trees do it, green algae do it,
all kinds of plants do it all the time
to produce over 15,000 tons of biomass every second.
And even on such a big scale,
photosynthesis comes down to just a chemical reaction.
A plant or green algae takes carbon dioxide,
water and sunlight,
and turns those ingredients, sugar, oxygen
and usable energy for the organism itself.
Sunlight along with the whole process of photosynthesis,
happens in an organelle
within plant cells called chloroplasts.
Inside the chloroplast or stacks of discs called thylakoids,
that are filled with little green pigments
called chlorophyll.
To understand how sunlight goes from a photon
to usable energy,
we need a little background on the chemistry of chlorophyll.
These molecules have a long carbon and oxygen backbone,
with a big grid of carbon
and nitrogen surrounding a lone magnesium atom.
This makes it so magnesium has a single electron
in its outer most layer that's just barely hanging in there.
So when a photon comes into the thylakoid,
it's energy knocks that electron off the magnesium.
Here's where things get a little abstract.
Usually we think of that magnesium ion as a whole,
as positively charged, it just lost an electron.
But for all this to make sense
we need to reframe it a little bit.
Think of it more like a neutral magnesium,
a negative electron and a positively charged hole
where the electron used to be.
This is called an exciton, and it can store energy.
Those negative and positive poles
make it work like a battery.
But in order to make energy out of sunlight,
the plant needs to get that exciton to a reaction center
for a process called charge separation.
This involves taking the electron from magnesium
and transferring it to some nearby molecule,
so that it can create a stable molecule.
From there,
the chemical process of photosynthesis can happen.
But transferring that exciton is the hard part.
Chloroplasts can transfer energy
from chlorophyll to chlorophyll
until it gets to a reaction center
but that might be really far away.
Plus, chlorophyll are packed together super densely.
So how does the excites on know which way to go?
For years, we thought it randomly stepped
from molecule to molecule
until it landed at a reaction center.
But if that were the case,
the excitons were more likely to get lost
than to perform photosynthesis.
And that was kind of a problem,
because in the real world,
photosynthesis happens with nearly 100% efficiency.
Almost zero electrons ever get lost,
and that's more efficient than any human technology
we've ever come up with.
Plus, classical chemistry couldn't explain
how such an efficient process was.
- This is a longstanding puzzle in biology,
and the article that the MIT physicists
were all laughing at,
was suggesting that plants use quantum mechanical effects
to get around this.
See one of the main ideas in quantum mechanics
is called superposition,
and it's the idea that a particle can be
in more than one place at a time.
In the macroscopic world we're accustomed to,
if something is in one spot,
it definitely can't be in any other spot,
but in the quantum world, things aren't so straightforward.
A single particle can simultaneously exist
in many different places with different probabilities.
It's kind of like if you have a hedgehog in a box
and you have to guess where it is.
You might say a 70% chance it's where the food is,
a 20% chance it's on the bed,
and a 10% chance it's on the treadmill.
These probabilities represent the likelihood
of finding the hedgehog when you take a look.
But the thing is,
the hedgehog isn't really in all of these places,
it's only in one, you just don't know which.
But quantum particles at different,
before they're measured,
they really are in all places at once
with different probabilities.
We can view these probabilities as a spread out wave.
At every point in space there's a different probability
of finding the particle there.
An important point is,
this probability wave only remains intact
before it's detected.
As soon as it's measured,
it collapses into a single particle at one location.
Yeah, there's a reason quantum mechanics
has a reputation for being weird.
Now this idea of being in many places at once
can be extended to taking many parts at once.
If a particle reaches a fork in the road,
it doesn't need to choose, it can take both.
If it's presented with many paths, it can take all of them,
like a wave spreading out over space.
This is exactly what the paper was proposing.
That the exciton takes all possible paths
to the reaction center,
and that's how it gets there so quickly.
This explanation actually kind of makes sense
when you think about it.
So why were all the quantum physicists
laughing their heads off?
Well, the biggest enemy of all quantum processes
is something called decoherence.
(air whooshing)
Remember how we talked about how the superposition
only lasts until a particle is measured?
Well in quantum talk,
measured doesn't mean the same thing
that it means in everyday language.
Here, measured means when this wave particle
comes into contact with anything else,
like another particle, a molecule, anything.
When it's in this wave state,
it's said to be in a state of coherence.
When it's broken or measured, this is decoherence.
Decoherence is the reason
physicists need to work in such specific conditions
when they're dealing with quantum mechanical effects.
In the macroscopic world we're used to,
there are so many particles and molecules bouncing around,
so much jostling and wiggling due to the heat,
that *coherence doesn't last long enough to be detected.
This is why we don't see quantum mechanical effects
in our day-to-day lives.
It's also one of the main struggles
with the creation of quantum computers.
Physicists come up with all kinds of clever
and expensive ways to shield their precious particles
from the evils of the outside world,
cooling them to near absolute zero temperatures
and attempting to keep them in complete isolation.
But so far, nothing has worked to keep decoherence at bay.
And now this paper was suggesting
that plants could ward off decoherence,
at normal temperatures and conditions?
It didn't make sense.
The MIT physicists sent one of their members, Seth Lloyd,
to investigate this claim.
What he came back with, surprised everyone.
Let's take a look at this paper which caused such a stir.
An experiment was performed
at the University of California, Berkeley.
Using a technique with the very impressive name
of Two-dimensional Fourier-transform Electron Spectroscopy.
The research team was able to probe into the inner structure
of a photosynthetic complex.
They fired three successive pulses of laser light into it,
which generated a light signal,
which was then picked up by a detector.
If there really was coherence among the excitons,
they should be able to see interference
between the different pathways or so-called, quantum beat.
(upbeat music)
The leading author on the paper, Greg Engel,
spent the entire nights ditching together the data,
and found exactly what he was looking for.
A rising and falling signal,
likely interference pattern produced when waves interfere.
In other words, this quantum beat showed that
the exciton wasn't taking a single route
through the chlorophyll maze,
but was following multiple routes simultaneously.
This was a huge shock to the scientific community.
The MIT physicists were forced to admit
that they may have laughed too soon.
Numerous experiments have been performed since then
confirming this result.
However, the story is far from over.
Although this quantum beat keeps showing up,
there's still debate over how to interpret it.
Some experts in the field
think that the beats are caused by molecular vibrations,
not coherence.
Others think the observed coherence
was too small in amplitude to have originated in excitons.
And then there are others who think
that this quantum beat is in fact direct evidence
for quantum biological processes.
Let's just say there are mixed vibes.
Research is still going on to understand
how photosynthesis is so efficient,
and may lead to insights to create quantum computers
and other technologies.
Quantum biology is an amazing area of research,
rich with possibilities.
This video was about the biological processes
that plants use,
but what about the processes that govern our own bodies?
In the next part of this series over on Pat's channel,
we'll see how a quantum biological process
may be responsible for the engines
that run our own bodies, enzymes.
I've linked to it in the description.
Make sure to check it out and subscribe to Pat
while you're over there.
I will see you in the next episode of Up And Atom,
where we talk about how birds may use quantum entanglement
to navigate the globe.
As always a huge thank you to all my Patreons on Patreon
who help make these videos possible.
Thank you for watching,
and I'll see you in the next episode.
Bye.