Caught in a Tractor Beam

How can light pull microscopic objects? What are the different ways scientists can use light to move stuff? What are some applications of these tractor beams?

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Episode Transcript

Speaker 1 (00:00):
Brought to you by Toyota. Let's go places. Welcome to
Forward Thinking. Hey everyone, and welcome to Forward Thinking, of
the podcast that looks at the future and says there's
a light in the darkness of everybody's life. I'm Jonathan Strickland,

(00:21):
I'm Lauren Folke Obama, and I'm Joe McCormick. And today
we wanted to talk a bit about tractor beams. As
it turns out, tractor beam. Yeah, tractor beams. So, so
we're talking about science fiction. No no, no, no, no no,
that would be a later podcast. Right now, we're talking
about science fact, science fact factor. Tractor beams. Yeah, tractor
beams are a real thing. Yeah, using fact like f

(00:42):
a k T fact exactly like f a k T.
So you're you're telling me, they're telling you're telling me
they're a real tractor beams in the world. It's amazing
to me that you don't know this because you wrote
the script for that particular episode and I've already recorded it.
But yes, there are. Do you just not believe your
own research. We're playing a little fantasy game. I'm sorry, Okay, yes,

(01:03):
what tractor beams? Well, I'll admit that even though I
did write a script about it. It's still blowing my mind.
You know what. It blows my mind too, because you're
sitting there talking about a phenomena that is incredibly counterintuitive,
right right, Well, I mean, you know when when we
see it in Star Trek, it looks like this beam
of light is pulling something towards it. And how does
how does that work? Because light pushes on right, Well,

(01:25):
we actually are talking about light. I don't want to
nerd out on you, but in star in wait, did
you say Star Treker star Wars? Oh? Then you're right,
You're totally right. You're totally right. I'm so sorry. I
thought you said Star Wars and I was gonna be
You don't see anything, okay, you just feel it. You're
just being pulled in, right, They got us locked in,
that's true. Yeah, they got us locked out of the track.

(01:45):
You don't see waiting until one is right there over
at the tractor beam controls that are rightly located next
to the enormous pit, that big beam going up and down. Yeah. Okay,
so I will save that for the next podcast, all
the sci fi stuff. Just just let it be known, okay,
for the like one person in the world who doesn't
know what a tractor beam from science fiction is. It's

(02:07):
a force that pulls you toward it, right, right, So
in science fiction it's often used for a ship to
be guided into the docking bay of some other vessel
or spaceport, or it's some way of capturing another object
peacefully without blowing it to smithereens and kind of grabbing

(02:27):
it taking it with you. Yeah. Yeah, so it's kind
of like a nons like a like a beam winch right, right. Yeah.
If you don't want the equivalent of having to fire
out grappling hooks from the side of your spaceship so
that you can pull some other spaceship in so you
can board it and and be space pirates, then you
need some sort of electronic electromagnetic version of that. And

(02:49):
and tractor beams tends to be the go to um
magical thing that we talk about to have this happen.
And as it turns out, we actually have developed a
type of tractor beam, a couple of different types of
tractor beams, but they're on a very small scale and
they use light. Astonishing, Yeah, they use light. They use light,

(03:10):
so they can shine light and pull something toward the
light source, which is incredibly counterintuitive. Like you were saying, Lauren,
I mean the light is something that pushes, right, It
has momentum. It behaves as both a particle and a way. Yeah,
it's even that's not totally intuitive, right, we should stop in.
Some people might be going, wait a minute, what light pushes? Yeah,

(03:31):
it does. It does have momentum. It has a relativistic mass,
which mostly means it as a mass that works out
in math, if not in what we would consider real
life situations. But it does have momentum. It can press
against something. Yeah, you call this the term is radiation pressure.
So you if you imagine the Sun, it's got raised

(03:54):
coming out of it in all directions. It's also got
solar wind. So you can understand why solar wind would
push because that's massive particles. So that's a little lasting
particles out into space. So if you have something like
a solar sale, which is a spaceship that's designed to
ride the force of the Sun outward from the solar system,
that's taking some of the force from that solar wind

(04:16):
those massive particles coming out, but some of the force
pushing it is just all it's light Yeah, it's photons.
It's just photons pressing against that solar sale. And because
you're not dealing with gravity in any in any appreciable sense,
once you get out into interplanetary space, as long as
you're not getting too close to any particular large body,

(04:39):
then you can use that to accelerate your spacecraft and
and travel and use that as a propulsion force. In fact,
that's one of the ones that that scientists have proposed
as a potential propulsion force once we're building spacecraft in space.
In fact, you don't even have to look at a
hypothetical spacecraft to see the force of radiation pressure in
our solar system. Right, you can look at like a comet. Right,

(05:03):
Comets tails always point away from the Sun. Yep, yep.
That tail is always going to be pointing away. And
that's because of this this pressure that we're talking about.
So that's Kepler discovered that, by the way, which which
comes up a lot in a lot of these articles. Yeah,
Kepler was a smart cat, let me tell you. So
we're getting into a smart human being. But yeah, well

(05:26):
Shortinger had a smart cat only half the time. So anyway,
the the the whole point of this is that if
you're thinking about an energy that has a pressure, like
it's pressing against something, how could that then draw an
object toward the source of that pressure. I mean, that
is very much counterintuitive, right, And the thing is is

(05:47):
that physicists have figured out ways of getting around this,
so that what's really happening is the light is pushing
on objects from behind and and thereby making the appearance
that it's pulling that object towards right. So so really
what's happening is that there's some sort of pressure building
on the back side of an object in relation to

(06:08):
where the source of light is, so that that pressure
on the back is pushing it towards that light source.
It's not truly pulling, Like It's not like if I
grabbed Joe and then just started to pull him towards me,
that that would be one thing. But this is more
like I signal to you, Lauren, and I pushed Joe
and towards you. By the way, this happens constantly in

(06:28):
our podcast, and I meant to bring that up earlier
suggest that we not do that, But really, I guess
it's a discussion for another Come on, guys, the examples
you're using are different in like eighteen ways. I want
to see the proof. What does this really look like
in the lab? What are they doing? All right, Well,
there's a couple of different ways that scientists have looked
into using light to uh to pull objects. First of all,

(06:51):
we should say that for a couple of decades now,
scientists have been using light to immobilize tiny, tiny, tiny
object right, So they're they're not wiggle. So in this
case you're using light. You're using light, it's not it's
not drawing it towards the source of light. It's just
there to either move something laterally, or you're just immobilizing something.

(07:15):
This is really important if you're dealing with really really
really tiny objects, like in organic chemistry or any kind
of biomedical research, you would need to be able to
to uh isolate and and uh and immobilize these tiny
tiny particles. I imagine we're talking about like the microscale
nanoscale is Yeah, microscale nanoscale is really what we're talking about.

(07:38):
Not keep in mind not so a nanometer is one
billionth of a meter, uh, a micrometer is one million.
So we're talking between the a few hundred nanometers to
a couple of microns in size. Uh. Now, one of
the ways that UH scientists have used is relying on
something called a bessel beam, which is a very peculiar

(08:00):
type of light. Yeah, a vessel beam. Uh. If you
see a vessel beam shined against a wall, you would
probably see something that looks like a target. It's like
a bull's eye with concentric circles coming out. Um. But
and that that's the way I've seen it in all
the videos and images I've seen online. But the essential

(08:20):
thing about a vessel beam is that it's non refractive, right,
so it stays focused over a really long distance. And
so if you're using a laser beam, we think of
laser beams as being really really concentrated beams of light
that don't tend to diffuse, but they do over great distances,
whereas a vessel beam maintains that coherence. Yeah. And the

(08:40):
other really weird and kind of interesting thing about a
vessel beam is that, if I'm correct, I think it
reforms after passing over an object. Right. Right, It's a
series of concentric circles of light that are formed around
a single dot, and that center point is created by
the light from the concentric circles, so it can it
can your form when something want to encounter something that's

(09:02):
path because it's not entirely being covered some of these
I see, So some of the outer circle is getting
around that object and therefore can reform that dot part
on the back side of that object. So it's not
the same thing as if it were to encounter, say
an enormous wall. It's more like if it had a

(09:23):
smaller object that would normally block that little dot, but
some of that concentric circle gets around, some of the
outer bits get around and behind. So the interesting thing
here is that you've got a laser beam that for
very tiny objects is uninterruptible, like it'll just it'll. If
you were to interrupt that light, it reforms on the
other side. It almost seems like magic when you think

(09:44):
about it, because it's like, uh, you've you've blocked off
that little dot from the source, and yet it still
reappears on the other side of the object. So if
a beam of light can reform on the other side
of an object, I wonder if there's a way to
time it so that when the beam hits the object,
it's at a low energy in its wavelength, and when

(10:06):
it reforms on the back of the object. It's at
a high energy. Well, gosh, Joe, it's almost like you
read that script you road, because in fact, that's exactly
what scientists have managed to do. They've managed to exactly yeah,
well with with with with two of these vessel beams.
When you when you yeah, yeah, when you when you
when you bend two of them together and kind of
focus them correctly, right right. What happens is you you

(10:27):
create a greater amount of pressure on the back side
of this tiny, tiny object. Remember we're talking about on
the micro scale here here. Uh, then you can create
enough force to push it toward what is the source
of that light. So, uh, it's exactly what you said, Joe.
You've got a lower amount of pressure on the front
side and a greater amount on the back side, and

(10:48):
that's what creates this movement. So this is one way
that scientists have discovered where you can actually use light
to move objects. Now keep in mind this is tiny,
tiny scale. We'll get into scalability issue. I know, Joe,
you're chopping at the bit to talk about that, But
we have another unusual and exotic way of using light

(11:09):
to manipulate objects. And in fact, it's this the second
method is incredibly technical, and we're really just going to
give an overview of it because to go into great
detail would one require that we'd actually bring someone in
who is a particle physicist, a particle physicist, because that's
how complex an optical physicist, Yeah right, you know, photons

(11:29):
of particles. But or we could uh this fight later,
geek fight um, or we can uh you know, so
we've had to either bring in an expert or we
would spend a lot of time gesticulating wildly in an
audio podcast room, which does not translate so well in
audio format. It's it would be fine for us, but

(11:50):
y'all listening might be a little bit, right, Yeah, so
we'll do our best here. Let's let's talk about this.
So it's this is from uh some some researchers who
are working out of both Scotland and the Czech Republic.
It's kind of a it's a it's a consortium of
of scientists and engineers who are working on this. And
and then this was just first published in on January.

(12:12):
So this is really cutting edge. Yes, this is really
really new and exciting stuff. But it's also the closest
thing to the Sci Fi tractor beam that we've seen yet.
It is and what's being used. They're using a Gaussian
laser beam. A linearly polarized polarization is referring to if

(12:34):
you think about the movements of a photon, they tend
to move generally speaking, this is really simplifying, but they
tend to move into planes, a horizontal plane, in a
vertical plane. Polarized light you can you can polarize light
in such a way so that it all moves within
a single plane, and then you can manipulate that plane
so that you are working with a very specific type
of light. We actually use this in UH practically in

(12:57):
three D applications. If you have passive three D glasses
that are the polarized lenses, then those lenses are polarized
in such a way to allow one type of light
through the lens while blocking another type. This allows you
to get two different um UH types of light in
you know, one in each lens, so that your brain
then combines the images that you're receiving into a single

(13:19):
image that gives you that illusion of depth. Right, So
it's it's tricking your brain into thinking that there's depth
there when really you're just looking at two different flat images. Okay,
but how do they use it so and to move
a little balls. All has to do with the geometry
of the light. First of all, we should say what
they are doing. They are moving tiny, tiny, tiny little

(13:41):
balls a little little styrene spheres that are suspended in fluid.
And I think one thing that's interesting is a lot
of these tests they seem to be dependent on the conditions, right,
so like we can move something this size in air,
or we can move something this size and a vacuum,
or and in this they were talking about suspended in water,

(14:02):
right And and this would obviously be something that would
be interesting again in biomedical UH applications, where you're talking
about lots of different fluids and particles that you might
want to be able to move around. One of the
cool things about this is depending upon the geometry of
the light that they used, they could manipulate certain sized
objects while leaving everything else alone. So you could be

(14:22):
very specific and hone in on exactly the size of
particle that you want to UH to manipulate while ignoring
all other particles. Wow, I bet that makes a lot
of people in medical apps salivate. Yeah, because you're talking
about sorting on an incredibly precise basis very exciting, like
a laser sifter, right right. What was really exciting to
me about this research is that they said that under

(14:44):
certain conditions, objects held by the beam would automatically rearrange
themselves to make the pulse stronger. I don't even know
what that means. That's yeah, it's we're getting into star
trek territory here with reversing the poet, and you're like
brain washing the balls the polystyrene spears, your brainwashing them

(15:09):
to do your bidding. Okay, all right, so these spears
tended to be but for the for this particular research project,
we're between about four and ten nanometers to one thousand
nanometers or one micron in size, and one thousand nanometers
that's huge to an atom. Yes, to us, it is

(15:33):
incredibly tiny. It's pretty big for being pulled by light. Yeah,
I being pushed around by photons. That's not bad at all. Yeah.
I can actually quote a little bit of this. So
here here's an example of how complex this gets, right
to the point where we would need to have a
specialist in here to really explain in Layman's terms, what's
going on there? We go The optical force originating from

(15:53):
the Galcian intensity profile normal distribution along the z axis
attracts the particles towards the center and so acts against
both the pulling or the pushing forces, as it was
explained in figures to A. B. C. Of the main text. Therefore,
if the beam is switched on or its polarization has changed,
the pulling or pushing forces propelled the particles to their
new equilibrium positions established in the Gaussian beams. To develop

(16:14):
an appropriate theoretical description of the geometry, we need to
take into account not only the Gaussian beam intensity profile
dragging particles to the beam center, but also the influence
of the scattered field reflected on the mirror back towards
the particle. This means that they were using a mirror
to um to help create interference within this Gaussian beam,
and Gaussian beams, we should say, are our beams that

(16:34):
are stronger in the center than they are at the
at the outsides. So again, it's similar to that vessel
beam approach where they were using two vessel beams in
order to interfere with one another and create that pressure
but in this case, you're using a beam to interfere
with itself, one beam in a mirror. Yeah. And the
other thing that's interesting that uh you you might not
have caught from that passage you read, but they can

(16:57):
change how the beam interacts with the particles by messing
with the polarity. Right, So if you tweak the polarity
of the beam, you could say push instead of pull. Right. Yeah,
So it gives you a lot of different options for
manipulating these these uh, microscopic or smaller objects. Now it's
you know, this lends itself to lots of different applications. Uh,

(17:20):
and that we're just starting to kind of consider right
now because we're still in the very much the early
early stages of developing this technology. But you could hypothetically
sort um different kinds of particulates out of something that
you didn't want in there. You could use it to
sort um diseased cells versus healthy cells, or or bacteria
versus healthy cells. Right. If the stuff you wanted to

(17:41):
take out of a solution, whether it was within a
person or in a you know, some some sort of
chemical whatever. Um, as long as that stuff was of
a very specific size, that was different from all the
stuff you wanted to leave in. This would be a
great way of doing it because you would know automatically
that your methodology you was not going to pick up
anything you didn't want. It was just gonna concentrate on

(18:04):
the stuff you wanted to remove. Because again, that geometry
only allows this light to interact with particles of a
specific size and it ignores everything else as far as
the pulling is concerned. You know, there's another good tangent
on what these types of lasers can do in in
tiny town. Uh, they said the vessel beams, So the

(18:24):
one from the first study we talked about that. They said,
those are really cool for what's called optical injection. So
what is that. That's where you use a laser to
stab a hole right in a cell and that allows
things that you're trying to put in the cell to
flood in. Gotch. So if you wanted to without necessarily
killing the cell. Right. So, So, if you're doing some

(18:46):
medical research and you really needed to be able to
manipulate cells on an individual basis and see what a
particular type of medication perhaps might do, or if you
just need to study the cell and you need to
insert some form of chemical so it will show up
on whatever imaging technique you're using. Then these could be

(19:07):
very useful techniques. It's kind of interesting stuff. So so Joe,
let's let's talk a little bit about scaling this up.
So we figured out that we can use light to
pull stuff what we want toward us. What if the
stuff what we want is really big, Like, let's say
it's not even that big. Let's say it's a I
don't know the size of a soccer ball or football

(19:30):
to our friends in Europe or or yeah, okay, or
or size like a podcast host or something like that.
Don't bring me into this. I don't want to get
burned up by your laser. Yeah. Part of the problem is,
uh so immediately, of course, when this study came out,
everybody is like, oh, yes, we've got tractor being. We

(19:50):
can reel in ships. We can, you know we can.
We don't have to worry about asteroids that because we
can just use the tractor beam to reposition it. Who
needs a tether for spacewalking anymore? Right? You know, you
go outside for a stroll. That's how the International Space Station.
You just take a walk. You get lost. Oh and

(20:11):
you're back home, and it makes that noise too, even
in the reaches of space. No. Part of the problem
is that, um, these beams require a lot of energy,
and if you were to scale them up so that
they were powerful enough to move heavier objects, they'd be
delivering more and more energy as you did that, which,

(20:32):
of course, when it strikes the object would turn into heat.
So you're essentially developing a thermal weapon as opposed to
a tractor beam. Yeah, it'd be like, well, it would
be more like a blaster if we want to stick
with Star Wars or a phaser. If we're talking story, Hey,
how about like a like a death Star planet killer
weapon and something like that. Instead of moving the asteroid,

(20:54):
you've just delivered a huge amount of thermal energy. Snow,
it's a really hot rock that's heading to our Maybe
maybe they were really just trying to move Alderan somewhere.
Maybe they didn't want to destroy it. I'm pretty sure
got off. Tarkin was pretty clear on his intentions, and
I don't even note see based on the scientists that
I read, I don't even know if it's technically possible
to pull things that at a huge scale, but I

(21:18):
know that this this heating up objection exists, so you
definitely destroy it in the process of pulling it, even
if you could pull it. So if you were if
you were a space station trying to pull a shuttle
into dock, then you would suddenly have this molten slag
coming towards your space station as opposed to you know,
that would be the best case scenario, right So anyway, Yeah,

(21:40):
so that that's why even with this amazing breakthrough, and
we don't mean to to diminish it at all. It
is phenomenal and really exciting stuff. It's it does not
mean that we are going to arrive at some sort
of science fiction future where we are going to have
these tractor beams in regular use, either here on Earth
or in space on the map acro scale. One thing

(22:01):
that I think it's really interesting is it's come up
multiple times now in this podcast. Is the place where
they're really thinking that tractor beam is going to be
useful is the small scale over and over inner space. Yeah,
I mean I wouldn't have even imagined that. Yeah, it's
it's super awesome and interesting. It's just not the way
that science fiction authors had envisioned it when they were first.

(22:23):
And really, you know a lot of the stuff that
science fiction authors create tend to be like placeholders, this
idea of there's this one problem that you would face
if you were out in space. How do we get
around that? What? What kind of what kind of technology
can we invent? So everything from artificial gravity to inertial
dampeners to warp drive things that help you get around
what would otherwise be huge problems When you get into

(22:46):
science fiction e. Space exploration type situations, Uh, you know,
you have to invent these these somewhat magical devices that
would counteract fundamental issues that you would run into otherwise.
Tractor beams are just one example of that. But there's
those fundamental physics are it's you know, still existent on
the small scale and are what we are much more

(23:07):
capable of of working with here on Earth. Yeah. Yeah,
And and there's no there's no reason to say that
tractor beams themselves will always be impossible on a macro scale.
They just won't be using lasers necessarily. We might be
using something else. But before we you know, dive into that,
I think we should say that for a completely separate discussion,
we're gonna talk about the science fiction of tractor beams,

(23:29):
how they've been used, and also some potential you know,
science fiction e kind of ways We might be able
to attain that in the future, assuming that the math
proves true and that some theoretical or rather hypothetical particles
actually exist. But that's that's something we'll say for the
next time. So guys, if you have any suggestions for
future episodes of Forward Thinking, please get in touch with us.

(23:52):
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