Evening ladies and Gentleman, welcome to the Moncure Conway - memorial lecture.
these lectures have been going on since 1910.
with not many interuptions--
there where a couple during the second world war.
although in fact there where occassions
on which lectures where held here
you'd be very pleased to know
that uh, during the course of one of them
a bombing raid occured
and a local church nearby was bombed
but not --- Conway hall.
*Light chuckle from audience*
(???)It's been uh-uh--uh a series of lectures by some  --amazingly distinguished people in the past
Bertrand Russell. (1872 - 1970)
A.J. Ayer. (1910 - 1989)
uh-- you name them really, they have been here and lectured here.
uh-- so these walls have had some interesting things.
and uh we have the very very great pleasure tonight indeed
to have my good friend, Lawrence Krauss
very distinguished physicist
and great communicator --uh about physics.
somebody who has done very important work in physics.
you will know those of you who have done your homework.
on Lawrence or have been avid readers of his for sometime.
that he was one of the theoreticians,
who spotted that there might be dark matter and energy in the universe
and then some folk, later on, went to make the observation, got the Nobel Prize for it
but they wouldn't have got it if it handn't been for Lawrence
And Lawrence is still active, still working, still busy in physics itself
But also busy as an activist
At the moment he's trying to bring down Donald Trump, before Donald Trump gets up.
*audience chuckle and applause *
But he's an indefatigable communicator about this very, very great adventure
the greatest adventure, really, of humankind
which is, the natural sciences
our understanding of the structural properties of the material universe
Here's somebody who knows something about it, who's going to tell us something about it right now
and by the way, this introduces
Lawrence's latest book. Not yet out on the shelves
but it soon will be.
And he will tel you about it in a minute.
Lawrence Krauss!
thank you
thanks
It is a pleasure to be back here
and it is an honour to be here during this lecture. It indeed, has had a distinguished history
as i was telling:
they ran out of the distinguished peopled and now they had to go for physicists like me.
But, uhm
So... I put this up - I'll come back to it, but the title of the story
which is the title of my new book, which is "The greatest story ever told" so far
and, uhm
and so i thought that I'd begin
as a good storyteller, in fact a good British storyteller
so i figured it's the best of times
And... And... And...
By that I mean that the large hadron collider is operating and has not created a black hole that would destroy the  world
But it is indeed also the worst of times
well, let's get rid of him, but... it's okay
And...
and
I put this up because physics lectures take us away from the myopic crap that we have to deal with
But also, what i want to talk about is really the greatest intellectual adventure humans ever taken
and in some sense the greatest aspect of being a human
And so, this is the worst aspects of being a human
and it's so nice that we can periodically rise above
the awful experiences we are having right now
and you will
Anyway, so let's go, now, back to the picture that I've started with
which is Van Gogh's "Starry night",
which is one of my favourite images of his
when i look at this
i wonder, what he was thinking, when he painted it, because
did he really see this image?
Picasso has famously said that he pained what he saw
and obviously lied
But you know, Van Gogh was kind of unstable
And so the question is:
is this what he saw, or is this the hidden reality that he saw was underneath?
when he looked at the sky, this is what he felt was underneath?
It's that hidden reality, which is the title of this lecture, that is interesting to me
because, we are hardwired to want there to be more to the universe than we can see
and science has certainly provided the fodder for that
The science has discovered many aspects of the world that we can't see, some of which I'll talk about.
It's also been responsible for religion.
But it's this notion that there really is a tip if a cosmic iceberg that we're somehow seeing
and the question i have is: what if this is what he really saw?
okay
what if the world was an illusion?
what if the world that we see now is the illusion?
And that's the subject that i want to talk about,
because it really is! The world we see is an illusion.
And a better example of that
is this image which i'll come back to
which is icicles on a window
which may, again, it may get cold enough one day here to have
... although not if Donald Trump has anything to do with it.
So...
They're beautiful. And it's interesting to look at this pattern on a window.
But when you do,
you notice that the crystals are all in different directions, there'ss nothing particularly special about them
But ask yourself:
What if you lived on once of these ice crystals?
what if you lived on this one right here?
what if you're a physicist living on this ice crystal?
What would the world seem like to you?
Well it would be obvious, first of all, that there's one direction that is very special
That direction there.
And the laws of nature would be very different in that direction, than they would on the perpendicular
... to that line.
And so, the experience you'd have is that it was natural, ingrained that the very central property of your existence
was the fact that this direction was special.
And religions would be based on that.
That somehow that direction was ordained by god
and designed so that you could live in the world in which you're living.
And the point is:
this is an illusion.
And it's the illusion we could see because we are outside of that system.
Wouldn't it be amazing if scientists on that crystal could somehow divine that the real world is quite different than the world they're seing?
And that's the story that I want to tell you about.
That the revolution that's really taking place over the last century
in our fundamental understanding of the universe, of matter and of energy on its small scales
that has revealed
this illusion we have.
But also revealed that things that we hold dear,
including our very existence,
are an accident.
That...
the illusion of design, among other things that we see, is an accident.
So that where i want to go.
And that's the story I wonna tell
and I do think that it's the greatest intellectual journey that humans have ever taken.
And it saddens me that it's no very well understood.
And i'm very happen that I've written the book, the last book about it, because
many people think of the 20th century revolutions that have taken place
(Einstein, quantum mechanics)
but there's actually a period much more recently,
where in fact, I think in the far future, when people look back
they'll say that the most revolutionary period of the 20th century
was not 1905,
was not the 1920-s
but it actually much later.
But that is not well known and i want to relate it to you now.
Okay.
This is our universe.
As seen in a rather grainy image right now.
But this is the Hubble Deep Field image.
We already know...
My last book in some sense
was about the fact
that this image in some sense on the larger scales is sort of the illusion.
That the important stuff is not the stuff we see, but the stuff we can't see.
And that really dominates the universe.
And in fact I've lectured in this hall, this very hall about that subject.
But i want to go back to saying
"well when we look at this universe, that inspires us to think about what cause all this.
And I go back
and it's not just because my friend Anthony Grayling introduced me, that i want to begin with philosophy
But as many of you know, I'm a grat lover of philosophy
And I begin with this fellow.
And whenever I ask who this is
and i'm not going to do this
because I don't want to embarass you.
Everyone says "Aristotle".
And it isn't.
And it's... Plato.
And uhm...
for me Plato was profoundly important because I was forced to read him when i was
in highschool.
I grew up in Canada, where they educate you
And uhm...
*audinece chuckles*
And they...
And so...
I read Plato's "Republic"
there was a
part of "republic" which has stayed with me ever since:
the allegory of the cave.
It...
And so i went back to my highschool book
and i found a drawing from it, which is this
So Plato
argued that we are in fact what we s...
REALITY is not what we see.
What we see is the shadow of reality.
And he used this example of a cave...
He likened humans to being individuals in a cave,
...chained to a cave, so that they could only see the walls of the cave
and the outside was here and
the light form outside came back
and also there was a fire behind them and they could see people on this roadway
but they could only see the shadows
So their world was just a shadow of reality.
And he said "well you know"
"the job of the philosopher-mathematician is to discern"
"based on those shadows, what reality really is"
...The job of modern physicists...
And he said that if you
...You can try and do that, but if you ever dragged out to the sunlight, not only would it be incredibly painful
and disturbing to see the true nature of reality
but if you ever
did settle down and see it, if you came back and tried to relate to the people back in the cave
what you'd seen - they'd think you're crazy.
And as a physicist I'm familiar with that feeling.
Because, the esoteric nature of particle physics
is so far removed form human experience - that many people give up,
but also say, you know...
"What's the point" and "it doesn't make sense"
The other thing in the image, by the way, which is interesting:
this is dated. It dates me.
Because this book is from late 1950s.
And you notice that the people that are bound
here on the wall
are scantly clad women in bikinis.
Which i think is...
Although i understand actually
Donald Trump's labour secretary uses that now in his ads as well
But uhm...
But it is historically wrong
because in Plato's time it would have been young boys
But in any case
Those individuals would have seen a reality that is different to the reality that we're privileged to know about
cause we live outside the cave.
But we can imagine some of the misrepresentations about reality that they may have had
And one of them is this:
they'd have no idea of length
We know what length is. Things have fixed length
and we were familiar with that here
In the cave, length would have no meaning to them
Because they might see that the shadow of a plastic ruler, say, behind them
would (???)
And at some times of the day it would look like that
and in some times of the day it would look like that, and they'd say
"well, clearly, objects change their lengths randomly"
And then
if there was a sufficiently intuitive
and thoughtful philosopher
that person might say
"you know what? Actually, we're seeing the shadows of reality"
"And what we're really seeing is a 2-dimensional projection of a 3-dimensional universe"
And so, just as...
Let's see... Oh yeah, Okay!
So, you know
my arm is this long here, but you see if I
rotate my arm it gets shorter
and if you couldn't see that, I'll just show you with this
here
so if we look from above here
if i have a ruler that is parallel to the wall - the shadow of the ruler is that long,
but of course, if i rotate the ruler in this extra dimension
then the projection of the shadow on the wall becomes smaller
So, if
the philosopher, mathematician, scientist eventually was smart enough to realize this, he'd say:
"really there is such a concept of length"
"but the real world is 3-dimensional and we're only seeing a 2-dimensional projection"
"And so length has physical meaning."
So that would have been interesting.
And that gives you an example of the kind of things
that you have to think of about that go beyond your experience.
and we'll come back to this in a bit.
Cause I want to jump ahead.
to this guy here
and you're a British audience, so you may know who this is
who is it?
Michael Faraday, that's right.
The greatest
The greatest experimentalist of the 19th century.
An amazing individual in many, many ways
in fact
But not least, because he achieved his eminence without any formal education.
he was a book binder's apprentice.
And i was just telling the students
at Anthony's College, that they uhm...
there's a valuable lesson to be learnt from Michael Faraday if you're a student
which is to suck to your professors
he attended the lectures of Humphry Davy that was head of the Royal Instituation
Not far form here.
And he
He attended those lectures and he took beautiful notes
and then bound them in a book
which he then presented to Humphry Davy and said "can i be your assistant"
And of course, he became his assistant.
And eventually rose to become the head of the Royal Institution
And in fact, i think he may have even established the Christmas lectures, I'm not sure.
Which he gave for many years.
But Faraday
because he wasn't trained
as a
Had no formal education - wasn't comfortable with mathematics.
...in general. In fact he said that he only wrote down only one equation in his life.
but of course, he discovered
the laws on which
everything in this room is based.
Ultimately the laws of electricity and magnetism that govern our lives.
And he did it with the laboratory with lots of esoterica
Which I also...
This is a story I like to politicians, because
it didn't seem very practical at the time
and there's at least an apocryphos story, or two or three: I've heard different versions of it
About... someone like Gladstone coming into his labratory and looking down and seeing these
frogs jumping, and all these other things happening
...wheels, and...
And... and... and...
"So what use is any of this?"
And there's two answers that
Faraday used... Well, two different answers I've heard that Faraday was supposed to give.
And one was: "of what use is a newborn baby?"
well, that's okay...
But the better one he said is
(???)
this is so useful that one day you will tax us for this
and he was absolutely right because he established the laws that the electric power is based on.
And we get taxed for it now.
Now he
he had problems with maths, as I say, and he
therefore used
crutches. Mental crutches to try and understand
pictorially, what was happening.
Say, with the simple repulsion of two electric charges
And in a sense, he answered the question that Newton himself
had left aside.
Newton
discovered the laws of gravity, of course, but never answered the question:
"how does the Earth know, where the sun is, to fall towards it?
just figured out how glad he would
but didn't worry about the wh...
you know, why the Earth knew the sun was there
And in fact
So this is same problem with two electric charges
How does one electric charge know the other electric charge is there?
And Faraday
resolved this, in a way, with his mental crutch.
he pictured an electric charge as having these
lines going outside of it
and the number of lines would be proportional to the magnitude of the electric charge
and called that "the electric field".
And then he could understand what happened.
He said, "well if I put another charge down somewhere in space
it doesn't know that charge is there
it feels the field lines coming from that charge.
So if I put a metal positive charge here, it would be repelled in the direction of the field lines.
And it gets even better, because if I put
two charges together, they both have field lines, and the field lines repel,
so i can sort of
imagine how you draw them
And the interesting thing is:
these were exactly right!
they reproduced the mathematics, the algebra of the electric field perfectly.
So they're an exact representation.
This crutch gave him all the answers.
So you know, for example,
if you put a positive charge right there - it's going to zing off in that direction.
And in fact, there's twice more field lines there, as there.
So the force would be twice as big as that
And it all warps out beautifully.
So that was just a mental crutch for him, these electric fields.
So hold that fact for a second
The other thing he discovered was...
(and i think the reason we really remember him)
was that...
Up to that point is was well known
that there was some relationship between electricity and magnetism
That if you moved a charge
and had an electric current you create a magnet.
That was well known. The French had shown that.
And, uhm... Uhm...
And so - fine! And so people said
Well if a magnet can create an electric force,
in itself, an electric force can create a magnet,
okay
and make a charge move along - and it makes a magnet,
and then it can attract another magnet,
(so moving charge can create a magnetic field)
Can a magnet affect a charge?
It should be reciprocal in some way.
And people have tried for the longest time and couldn't.
And, you know, they brought very strong magnets
(???) charges, and they couldn't get anything happening
And Faraday, by accident of course, discovered the relationship.
He had two current loops: one connected to a battery and another one - not.
(???)
And he turned on...
And he connected to the battery, so current began to flow a little
and it became a magnet
suddenly a charge flowed in that other loop.
what he discovered was that a changing magnetic field
because of that becomes a magnet
it starts out of zero and becomes stronger
a changing magnetic field could produce an electric force in that (???)
So...
So indeed there was a reciprocal relationship, in some sense:
A moving charge could produce a magnetic field,
and a changing magnetic field could produce a force on a charge.
And ultimately
that created
an important step.
Which in fact, the next person I want to show you finished.
This is the most famous theoretical physicist of the 19th century
and the greatest.
Who's this?
Actually, I love the fact that we have a literate audience - it's great.
okay.
James Clerk Maxwell, who was an amazing guy.
Scott.
And...
there's interesting history: he died very young, but he still did...
(younger than many people in this room)
but he still did an incredible amount in that time
And...
He...
he was a mathematician. He was mathematically literate.
And so... What he did... Was he...
realized that in order to make the discoveries that Faraday has made,
to make it all consistent
you had to fix things up,
and he made what we now call "Maxwell's equations"
The four Maxwell's equations that
undergraduate physics students have on their chest
(???)
The four equations, then, "let there be light"
because
because not (???), but Maxwell demonstrated how there would be light.
Because what Maxwell discovered
and it is indeed American in the most
exciting calculation you can do as an undergraduate physicist, i think.
It is...
he realized the (???)
If I take a charge and shake it
okay
...then...
What's happening?
Well i'm having a current that's...
...that's...
first of all, I have a current, so I'm producing a magnetic field here
but the current is changing
so the magnetic field I'm producing here is changing
But if I ch...
The changing magnetic field - this changing magnetic field is going to produce electric field here
which is changing
but that change in electric field here is going to produce a magnetic field there
...that's changing...
...that's going to produce an electric field here...
*unintelligible accelerating speech*
And...
You're going to get a disturbance
that travels out
and the amazing thing is: by measuring
the strength of the force between two electric charges
in the laboratory
and then by measuring the force between two magnets in the laboratory
measuring those to fundamental constants of nature
he could calculate what the speed of that disturbance would be
and learn... well when you do that calculation you discover it's the speed of light.
that was measured...
...speed of light...
Thereby answering the question: "what was light?"
(which had been around since before Newton)
And discovering that light was a wave of electric and magnetic fields.
And...
that was amazing!
Because electric an magnetic fields were an intellectual crutch
that Faraday developed in his mind, because he could not do the math.
But they weren't just the invention of the human imagination
they were as real as a hand in front of your face
because you wouldn't see the hand in front of your face
It's the electric fields, it's light itself.
So...
This imaginary thing that Faraday developed turned out to be essential.
But it also meant that they completed this most amazing unification
(the first amazing unification in physics)
Two things which seemed very different
an electric field and a magnetic field
which seem to be really - different aspects of exactly the same thing
One person's electric field - would be another person's magnetic field
It just depended upon what you were doing
if you're standing next to electric charge, and you're a charge - you feel electric force.
but if you're running compared with that electric charge
that charge is moving with respect to you, and you feel a magnetic force.
So really they're different faucets of the same thing.
And that is the hallmark of progress in science
When disparate parts of our universe are seen to be reflections of the same thing.
Just like for Plato's people.
That in fact different length object are seen to be different reflections of the same thing.
that's the hallmark of progress.
and that's what you generally look for and understand as being real development.
So that...
...that beautiful development of Maxwell's
completed the great unification - the first great unification of physics.
That was in the 19th century.
And...
Then we now move to the 20th century.
Ah, I just have a picture of the electric field, but let's skip that because...
...there it is...
But we will skip it eventually when this thing stops.
There you go.
This guy! we'll you all know who that is. I don't have to ask.
okay
You've all heard of him.
And... And... And... It's intersting
uhm...
He is a...
a paradigm, for people.
And he affects many of us in many ways.
In my case, everyday I get about five emails
from people
who tell me the following:
everyone says I'm crazy
they say.
But everyone said Einstein was crazy.
Therefore...
*audience laughing*
And then they say... And this is the real kicker
cause this is when I know to press "delete".
they say "everything you think you know - is wrong"
"all of modern physics is wrong."
"And just like Einstein, I can show you that it's all wrong"
"cause that's what Einstein did - he showed it's all wrong".
But they
demonstrate: it's a profound misunderstanding of science!
Scientific revolutions do not do away with what went before them.
In fact, what survives the test of experiment -
will always survive the test of experiment.
It will always be, in some sense, true.
Newton's laws - simple laws of motion
having been supplanted at scales...
small scales by quantum mechanics, large scales - by general relativity,
but they're absolutely true for the motion of baseballs and cannonballs
...and cricket balls (to the extent that anyone cares about that)
uhm...
And... and...
And...
and so...
What Einstein actually...
The brilliance of Einstein was quite the opposite.
What Einstein realized was that there were two aspects of reality that have survived the test of experiment
that were inconsistent with each other.
What was he going to do?
He didn't throw them out...
What he did was find a way to make them consistent.
So what are they?
Well, one - I've already given you.
I've already prepared your mind.
That's Maxwell.
Maxwell said, "If I shake a charge..."
"...an electromagnetic wave would go out..."
"...and the speed of that wave would be determined by measuring the strength of electricity,..."
"...the strength of the force of two electric charges in the laboratory..."
"...and the strength of magnetism"
Ok? So... that's there.
Now the other one, that was tested by a hundred years of observation, was Galileo
Galileo's great discovery
was that
that Aristotle was wrong, yet again.
At Anthony's i had 'this' debate, because
I'm profoundly influenced by that fact that it seems to me that Aristotle was almost never right.
When he talked about the physical world.
But Aristotle did, what, you know,
what human experience tells us.
Common sense...
Which is that all objects like to go to rest.
You move them - and they stop.
So being at rest is of special significance.
But what Galileo realized was that that's just an accident of our circumstances.
Because, you know, he gave these examples of...
If you slide on ice you don't go to rest very much.
if I have a ball on a very smooth platform - it will go a long way.
So things don't naturally go to rest
You can imagine, in fact, that if you get rid of this extraneous thing called friction...
...that the objects will go on forever.
And what he said, which laid the basis for Newton: that the natural state of motion
is to not change its state of motion.
Being at rest - you stay at rest.
But there's nothing different from being at rest, when moving at a constant speed.
In fact...
The way we frame what he said now is: There is no experiment you can do
that will tell you if you're moving at a constant speed, ...
...or at rest.
You all had the experience of being on a subway train here in London
...in the station, and for a moment, the train on the other side starts moving...
...and you don't know if you're moving, or they're moving.
And the answer's that you can't do any experiment... Until you start shaking - so you're not moving at a constant speed.
Or when you're in an airplane, if the windows are closed, and you throw a baseball up
or a coin - it comes back down.
There's no way you can prove you're moving.
Ok, It's just like you're standing still, like you're doing here. Right?
Wrong! Ok?
We're moving around the sun at 30 km per second right now.
30 km per second.
The Sun's moving around the galaxy at 200km per second.
But we keep saying we're at rest.
That's cause it feels we're at rest, that's cause there's no way to tell the difference.
...if we're moving at a constant speed.
Ok, those are the two things.
There is no experiment that will tell you whether you're moving or standing still.
That's Galileo.
Maxwell: "Shake a charge - it moves at the speed of light, determined by those two fundamental constants of nature".
Now, the average person may not see those as being problematic.
But Einstein realized that they were completely inconsistent.
And I can explain this to you.
The example I'm going to present - I first thought of when my daughter was very young.
So I will use projectile vomit as the... 
*audience laughs*
I used to drive her in the car, when she was young, to the nursery school
and she didn't like the car very much.
So let's say we're driving along at some slow speed in traffic, say 20 miles an hour...
And, so someone watches me
I'm traveling 20 miles an hour and someone on the ground sees the car go by 20 miles an hour
And she's in the back seat, and she projectile vomits and hits the back of my head
from the back seat to the front seat
And it goes at 10 miles and hour in the car
So the vomit hits me at 10 miles and hour
But, of course, someone on the ground watching that, laughing,
Sees the car moving at 20 miles an hour and the vomit at 10 miles an hour in the car
therefore the vomit is moving with respect to them at
30 miles an hour. 
What a great audience!
OK, great.
No problem.
But now let's say my daughter is a 20th century kid
and she has a little laser that she plays with
and so she shoots a laser beam at the back of my head.
Laser beam travels at the speed of light.
What does the person on the ground see?
Well, the car's moving along at 20 miles an hour
the laser's in the car, and the laser's in the car, moving at speed of light
so the person on the ground sees the light ray
as traveling at the speed of light, plus 20 miles and hour.
That makes sense.
The problem is: that's inconsistent with Maxwell, in a way.
Because, Maxwell says: when I shake an electric charge, like I do in this laser,
A light ray goes out, and it travels at the speed of light
and that's determined by the fundamental strength of electricity
and the fundamental strength of magnetism.
But that's inconsistent with Galileo,
Because the person on the ground sees the light ray
as being the speed of light, plus 20 miles per hour.
That must mean, in their labratory
the strength of electricity and the strength of magnetism is different.
Because Maxwell tells me
that the speed of the light ray is determined
by the strength of electricity and the strength of magnetism.
Therefore, this person on the ground sees it as at a different speed, than the person in the car.
That person on the ground must make a different measurement in their laboratory
for teh strength of two fundamental forces.
But Galileo says - that's not possible!
Because there's no experiment you can do, that will tell you the difference of whether you're moving or standing still.
So they both can't be right.
It doesn't work.
And the brilliance of Einstein was to realize:
well, they're both right, because they're both ...
...for hundreds of years - for Galileo, and  less than 50 years for Maxwell...
...those things survived the test of experiment.
They can't be wrong - we can't throw them out.
