Regularly once a month or so I've had an email saying "Have you come across gauge blocks?
Do you know what gauge blocks are? You know they stick together? How do they stick together?
Do they do..what's going on there? Is it due to a vacuum? Is it due to grease? Is it due to something else?"
(Brady) So, so Phil what are gauge blocks? I don't even know you talking about.
Great, so I had very little knowledge of what a gauge block was until actually this morning. When I did, I decided
I'd finally take a look, and go down to the workshop and talk to our wonderfully talented technicians.
And they have got a number of boxes of these gauge blocks.
So these are like measurement standards. Very precisely machined to be a certain number of millimeters.
So the surfaces are incredibly smooth, incredibly flat. Machined to be really, really flat and
what you can do is you can take two gauge blocks and just by pushing them together get them stick. No glue, no
jiggery-pokery, no magnetism. They'll just stick. (Brady) And what are they made of?
Just pure steel, which seems quite magical and so I want to try and attempt to do this.
It's a bit of a skill sometimes it seems to work sometimes it seems to not work.
I am sure the Brady has ever will leave in all the attempts that don't work.
But let's let's see. What I'm going to do first of all is just just put a little bit of acetone on
And clean off any crud that's on
On the smooth face. That's relatively clean now, and let's clean this one off. (Brady) You're drying it so there's no acetone left?
No, there's no acetone left now. I'm using the acetone to just take off any crud that's on there.
No, I don't think this is gonna work that time. No that time didn't.
No! So the way you're meant to do it is actually twist around to 90 degrees, but I've never
nearly!
I think I can get that to work this right before. There we . . .[expletive]
We'll just clean it again.
(Brady) Technicians know of the trick?
Yeah, no technicians use it all the time
It's not just a trick, it's
a way of stacking them up. And the reason why
it was introduced like this is because they didn't want to have a whole set of different calibration gauges
and this makes it much more straightforward to just add them up--if you can get it a bloody work!
Almost . . .
there we go! (Brady) Keep still! Keep still for me.
(Brady) So they're like stuck there, Phil? (Phil) They're stuck together, yep, and you know, force of gravity doesn't care. So that's you know,
it's a fairly hefty block and it's being held on there against the force of gravity. [Laughter]
What makes it happen? So that's been a question now people have--I'm getting quite okay with it now--
That's a question that people have asked a lot, an awful
lot over the last century, a 120 years or something like that, as to what the heck is going on.
So it's an effect that you see
when you have very smooth surfaces. Now, it just doesn't have to be steel.
Over here
I've got a couple of silicon wafers. These are very smooth as well, and what I'm going to do is
I'm going to put one on top of the other and apply a bit of pressure,
hopefully without cracking that.
Here we go.
Okay same idea.
(Brady) What's going on there? Two very smooth surfaces?
(Phil) Two very smooth surfaces. So there are number of different things. First of all, everything around us to a greater or lesser extent is covered
with a thin film of water.
Depends on how
hydrophobic--how much it doesn't like water--or hydrophilic a surface is. To a certain extent all
surfaces were covered with a molecularly thin film of water.
So that's one aspect of this on a molecular level that acts as a sort of glue, but even beyond that what's remarkable,
great
aspect of, how will we put it--the statistics of quantum physics in action.
But in this case the silicon wafers for example have got a thin film of oxide that's relatively hydrophilic. It likes water.
Similarly with the metal here,
relatively hydrophilic, quite likes water. However in the case of the silicon, what you can do is you can take a silicon wafer,
dip it into hydroflouric acid,
strip off all the oxide, and end up with a very hydrophobic surface, so as soon as you put water on it,
it beads up.
Those will still bond. And the reason they still bond, and these will still bond in vacuum even when you remove the water, the
reason they still bond is over here you've got fluctuating electrons, over here
you've got fluctuating electrons, and it's something called the van der Waals effect. In any given instance of time, there's a little dipole.
There's a little imbalance of charge so that you've got a region
which is slightly more positive compared to another region.
And those dipoles interact and snap things together so a whole area in the semiconductor industry called wafer bonding based on this.
(Brady) It's not like one's positive and one's negative? (Phil) No, no, absolutely not. It's exactly the same effect happens in atoms. So xenon,
for example,
you can condense that to form a xenon solid, and that's not because electrons are being shared,
or electrons are being transferred as in a covalent or an ionic bond. What's happening is it's this van der Waals effect.
It's, it's because there are fluctuations of the electrons, which
means that it's not like you've added a positive charge. It means that if the
fluctuations of electrons then this bit slightly got more electrons over here than it is over here,
so there's a tiny, tiny dipole. And it's those dipoles that give rise to this, this force.
Even though there's no transfer of charge, even though there's no sharing of electrons,
it isn't an ionic bond. It isn't a covalent bond. It's called the van der Waals force.
It's exceptionally important.
And that's what's certainly a contributor alongside any liquid film that might be there to what's holding these things together.
So you might be wondering why doesn't it sort of work in the opposite direction as well?
Why doesn't it correlate so that they just fly apart in terms of the way the charges line up?
So a key thing that can happen is that the dipole that forms here, on that instant moment of time, it can induce, it can
influence the electrons over here and includes them in such a way so that the net attraction that that happens there.
(Brady) Why did the surface have to be so smooth? Why don't you and I stick to each other?
(Phil) So that's a really good question. So you need those smooth because you want those--if you have asperities there, if you have sharp bits,
then what happens is your forces don't add up in the right way.
You don't get the interactions. Moreover, if the liquid film is important, the fact that you've got a
very rough surface means that that water film that liquid film can't act as a glue in the same way.
In some state called an entangled state
That's all we need to go into you
Send one particle to one end of the universe if the universes ends the other particle to the other end of the universe you make
A measurement on this one and here's the weird bit the bit, but course causes so many physicists so many sleepless night