So I have a question:

who here remembers when they first realised they were going to die?

I do. I was a young boy and my Grandfather had just died.

and I remember, a few days later,

lying in bed at night trying to make sense of what had happened.

What did it mean that he was dead?

Where had he gone?

It was like a hole in reality had opened up and swallowed him.

But then the really shocking question occured to me,

if he could die, could it happen to me to?

Could that hole in reality open up and swallow me?

Would it open up beneath my bed and swallow me as I slept?

Well, at some point all children become aware of death.

It can happen in different ways, of course and usually comes in stages.

Our idea of death develops as we grow older,

And if you reach back into the dark corners of your memory,

you might remember something like what I felt when my grandfather died

and when I realized it could happen to me too.

That sense that behind all of this, the void is waiting.

And this development in childhood reflects the development of our species.

Just as there was a point in your development as a child,

when you sense of self and of time became sophisticated enough

for you to realize you were mortal.

So at some point in the evolution of our species

some early humans' sense of self and of time became sophisticated enough

for them to become the first humans to realize: "I'm going to die".

This is, if you like, our curse:

it's the price we pay for being so damn clever.

We have to live in the knowledge

that the worst thing that can possibly happen, one day surely will.

The end of all our projects, our hopes, our dreams, of our individual world.

We each live in the shadow of a personal apocalypse.

And that's frightening! It's terrifying, and so we look for a way out.

And in my case, as I was about five years old,

this meant asking my Mum.

Now when I first started asking, "what happens when we die?",

the grown-ups around me at the time answered with a typical English mix

of awkwardness and half-hearted christianity.

And the phrase I heard most often was that Grandad was now

'up there looking down on us'.

And if I should die too, which wouldn't happen of course,

then I too would go up there.

Which made death sound a lot like an existential elevator.

Now this didn't sound very plausible.

I used to watch a children's news programme at the time

and this was the era of space exploration.

There were always rockets going up into the sky,

up into space, going 'up there'.

But none of the astronauts when they came back

ever mentioned having met my grandad.

Or any other dead people. But I was scared.

And the idea of taking the existential elevator

to see my Grandad sounded a lot better

than being swallowed by the void while I slept.

And so I believed it anyway, even though it didn't make much sense.

And this thought process that I went through as a child,

and have been through many times since including as a grown-up,

is a product of what psychologists call a 'bias'.

Now a bias is a way in which we systematically get things wrong,

ways in which we miscalculate, misjudge, distort reality

or see what we want to see.

And the bias I am talking about works like this:

confront someone with the fact that they are going to die

and they will believe just about any story that tells them it isn't true

and then can instead live for ever.

Even if it means taking the existential elevator.

Now, we can see this as the biggest bias of all.

It has been demonstrated in over 400 empirical studies.

Now these studies are ingenious but they're simple, they work like this:

you take two groups of people who are similar in all relevant respects

and you remind one group that they're going to die but not the other;

and then you compare their behaviour.

So you're observing how it biases behaviour

when people become aware of their mortality.

And every time, you get the same result:

people who are made aware of their mortality

are more willing to believe stories that tell then that they came escape death

and live forever.

So here's an example: one recent study took two groups of agnostics,

that is people who are undecided in their religious beliefs.

Now one group was asked to think about being dead,

the other group was asked to think about being lonely.

They were then again asked about their religious beliefs:

those who had been asked to think about being dead

were afterwards twice as likely to express faith in God and Jesus.

Twice as likely.

Even though before they were equally agnostic.

But put the fear of death in them and they run to Jesus.

Now, this shows that reminding people of death biases them to believe,

regardless of the evidence.

And it works not just for religion but for any kind of belief system

that promises immortality in some form,

whether it's becoming famous, or having children, or even nationalism

which promises you can live on as part of a greater whole.

This is a bias that has shaped the course of human history.

Now the theory behind this bias in nearly 400 studies is called

terror management theory. And the idea is simple, it's just this:

we develop our world views, that is the stories we tell ourselves

about the world and our place in it,

in order to help us manage the terror of death.

And these immortality stories have thousands of different manifestations.

But I believe that behind the apparent diversity, there are actually

just four basic forms that these immortality stories can take.

And we can see them repeating themselves throughout history.

Just with slight variations to reflect the vocabulary of the day.

Now I am going to briefly introduce these four basic forms of immortality story

and I want to try to give you some sense of the way in which they're retold

by each culture or generation,

using the vocabulary of their day.

Now, the first story is the simplest: we want to avoid death.

And the dream of doing that in this body, in this world, forever,

is the first and simplest kind of immortality story.

And it might at first sound implausible,

but actually almost every culture in human history

has had some myth or legend of a elixir of life,

or a fountain of youth or something that promises

to keep us going forever.

Ancient Egypt had such myths, ancient Babylon, ancient India,

throughout European history, we find them in the work of the alchemists

and of course we still believe this today.

Only we tell this story using the vocabulary of science.

So a hundred years ago, hormones had just been discovered,

and people hoped that hormone treatments were going to cure aging and disease.

And now instead we set our hopes on stem cells, genetic engineering

and nanotechnology.

But the idea that science can cure death

is just one more chapter in the story of the magical elixir,

a story that is as old as civilization.

But betting everything on the idea of finding the elixir

and staying alive forever is a risky strategy.

When we look back through history

at all those who have sought an elixir in the past,

the one thing that they now have in common is that they're all dead.

(Laughter)

So we need a back up plan, and exactly this type of plan B

is what the second kind of immortality story offers,

and that's resurrection.

And it's staged with the idea that I am this body,

I am this physical organism,

it accepts that I am going to have to die,

but says despite that, I can rise up and I can live again.

In other words, I can do what Jesus did.

Jesus died, he was three days in the tomb and he rose up and lived again.

And the idea that we can all be resurrected to live again is orthodox belief,

not just for Christians but also Jews and Muslims.

But our desire to believe this story is so deeply embedded

that we are reinventing it again for the scientific age.

For example with the idea of cryonics.

That's the idea that when you die, you can have yourself frozen,

and then at some point when technology is advanced enough,

you can be thawed out and repaired and revived and so ressurrected.

So some people believe an omnipotent God will ressurect them to live again

and other people believe an omnipotent scientist will do it.

But for others, the whole idea of ressurection,

of climbing out of the grave, is just too much like a bad zombie movie.

They find the body too messy, too unreliable to guarantee eternal life.

And so they set their hopes on the third more spiritual immortality story,

the idea we can leave our body behind and live on as a soul.

Now the majority of people on Earth believe they have a soul

and the idea is central to many religions.

But even though in its current form and its traditional form,

the idea of the soul is still hugely popular,

nonetheless we are again reinventing it for the digital age.

For example, with the idea that you can leave your body behind

by uploading your mind, your essence, the real you, onto a computer.

and so live on as an avatar in the ether.

But of course there are skeptics who say if we look at the evidence of science,

particularly neuroscience, it suggests that your mind, your essence, the real you,

is very much dependant on a particular part of your body

that is your brain.

And such skeptics can find comfort in the fourth kind of immortality story,

and that is legacy.

The idea that you can live on through the echo you leave in the world.

Like the great Greek warrior Achilies, who sacrificed his life fighting at Troy

so that he might win immortal fame.

And the pursuit of fame is as widespread and popular now

as it ever was.

And in our digital age, it's even easier to achieve.

You don't need to be a great warrior like Achilies or a great king or hero,

all you need is an internet connection and a funny cat.

(Laughter)

But some people prefer to leave a more tangible, biological legacy,

children for example.

Or they like, they hope, to live on as part of some greater whole

a nation, or family, or tribe, their gene pool.

But again there are skeptics, who doubt whether legacy really is immortality.

Woody Allen for example, who said,

"I dont want to live on in the hearts of my countrymen,

I want to live on in my apartment".

(Laughter)

And if you want to live on in your apartment

you need a elixir of course.

Which was our first kind of immortality story.

So those are the four basic kinds of immortality stories

and I've tried to give just some sense of how they're retold by each generation,

with just slight variations to fit the fashions of the day.

And the fact that they reccur in this way, in such a similar form

but in such different belief systems, suggests I think

that we should be skeptical

of the truth of any particular version of these stories.

The fact that some people believe

an omnipotent God will ressurrect them to live again,

and others believe an omnipotent scientist will do it,

suggests that neither are really believing this on the strength of the evidence.

Rather we believe these stories because we are biased to believe them,

and we are bias to believe them because we are so afraid of death.

So the question is, are we doomed to lead the one life we have

in a way that is shaped by fear and denial?

Or can we overcome this bias?

Well the Greek philosopher Epicurus thought we could.

He argued that the fear of death is natural but it is not rational.

Death, he said, is nothing to us,

because when we are here, death is not,

and when death is here, we are gone.

Now this is often quoted but it's difficult to really grasp, to really internalise,