Brian Cox on how black holes could unlock the mysteries of our universe

Summary

In this insightful discussion, Professor Brian Cox delves into the enigma of black holes, proposing them as the key to unlocking a quantum theory of gravity. He explores the historical roots of black hole theory, the concept of event horizons, and the perplexing nature of singularities. Cox highlights Stephen Hawking's discovery of Hawking radiation, which suggests black holes are not eternal but have a lifespan, potentially returning matter to the universe. The 'Black hole information paradox' is addressed, pondering whether information is preserved or lost within black holes. The discourse hints at a deeper reality where space and time may not be fundamental but emergent from quantum entanglement, offering a glimpse into the fabric of the universe.

Takeaways

• 🔑 Black holes might be the key to understanding a quantum theory of gravity, which would unify quantum theory and general relativity.
• 🌌 The event horizon of a black hole is a boundary where our understanding of physics is thought to be complete, yet it clashes with our current theories of physics.
• 🕳️ Black holes challenge our understanding of space and time, suggesting a deeper theory may be needed.
• 📚 Brian Cox, a professor of particle physics, believes black holes are crucial for understanding the universe.
• 📖 The concept of black holes dates back to the 18th century with ideas about escape velocity by Mitchell and Laplace.
• 🌟 The escape velocity of an object increases with its mass, leading to the concept of black holes where the escape velocity exceeds the speed of light.
• 🕒 The event horizon is considered the boundary of a black hole, where time appears to stop according to Einstein's theory of relativity.
• 🌀 The nature of the singularity, or the center of a black hole, remains a mystery and is considered the 'end of time'.
• 🌡️ Stephen Hawking's work showed that black holes emit radiation, known as Hawking radiation, suggesting they have a temperature and are not eternal.
• 🔄 The concept of black holes led to the 'Black hole information paradox', questioning whether information is lost within a black hole.
• 🌐 Current research suggests that black holes do not erase information, hinting at a deeper understanding of gravity and the nature of space and time.

Q & A

What is the significance of black holes in the quest for a quantum theory of gravity?

Black holes are significant because they represent a place where the event horizon challenges the clash between quantum theory and general relativity, potentially leading to a deeper understanding of space and time.

What is the 'event horizon' of a black hole?

The event horizon is the boundary surrounding a black hole that separates the external universe from its interior, where even light cannot escape the gravitational pull.

Why did Mitchell and Laplace's concept of 'escape velocity' lead to the concept of black holes?

Mitchell and Laplace theorized that if a celestial body's gravitational pull was strong enough to make the escape velocity exceed the speed of light, it would become invisible, leading to the concept of black holes.

What is the 'singularity' in the context of black holes?

The singularity is an infinitely dense point at the center of a black hole where the laws of physics as we know them break down, and it's considered the end of time.

How does the concept of Hawking radiation challenge the traditional view of black holes?

Hawking radiation challenges the traditional view by showing that black holes are not completely black but emit particles, suggesting they have a temperature and can evaporate over time.

What is the 'Black hole information paradox'?

The Black hole information paradox is the question of whether information about matter that falls into a black hole is lost forever or can be recovered through Hawking radiation.

What does the current consensus suggest about the conservation of information in black holes?

The current consensus suggests that black holes do not erase information from the Universe, and it might be possible to reconstruct the information about everything that fell in through Hawking radiation.

What is the 'emergent spacetime' theory?

The emergent spacetime theory posits that space and time are not fundamental but emerge from quantum entanglement or some other underlying quantum structure.

Why are black holes considered the key to understanding the Universe according to Brian Cox?

Black holes are considered the key to understanding the Universe because they force us to delve deeper into the nature of space and time, potentially revealing the underlying structure of reality.

What is the role of quantum entanglement in the context of black holes?

Quantum entanglement plays a role in the production of Hawking radiation, suggesting a link between the quantum world and the gravitational phenomena of black holes.

How does the study of black holes contribute to the understanding of the origin of the Universe?

Studying black holes contributes to understanding the origin of the Universe by providing insights into the fundamental nature of space and time, which are critical to theories of cosmic origins.

Outlines

00:00

🌌 Black Holes: Gateway to Quantum Gravity

Brian Cox, a professor of particle physics, delves into the concept of black holes as a potential key to understanding a quantum theory of gravity. He discusses the event horizon and the clash between quantum theory and general relativity. Black holes are significant because they challenge our understanding of space and time, pushing physicists to develop a unified theory. The historical origins of black holes are traced back to the 18th century with Mitchell and Laplace, who pondered the idea of escape velocity and its implications for massive celestial bodies. The concept of a black hole as a region where time stops, according to Einstein's theory of relativity, is also explored.

05:01

🔥 Black Holes and Hawking Radiation

The paragraph discusses the revolutionary idea that black holes are not static but emit particles, a phenomenon known as Hawking radiation. Stephen Hawking's papers suggested that black holes have a temperature and can evaporate over time, leading to the concept that they are not eternal prisons. This challenges the traditional view of black holes and raises questions about the fate of information swallowed by them. The 'Black hole information paradox' is introduced, questioning whether information about matter that falls into a black hole is lost forever or if it can be recovered through Hawking radiation. The current consensus leans towards the idea that information is not lost, suggesting that black holes do not erase information from the universe.

10:01

🌐 Emergent Spacetime and the Nature of Reality

This section speculates on the deeper implications of black hole research for our understanding of space and time. It suggests that space and time may not be fundamental but emerge from a deeper theory, possibly related to quantum entanglement. The concept of 'emergent spacetime' is introduced, indicating that our classical notions of space and time could be derived from more basic quantum phenomena. The discussion points towards the necessity of understanding the true nature of space and time to answer fundamental questions about the universe, such as its origin. Black holes are portrayed as natural phenomena that compel us to ask these profound questions and seek a quantum theory of gravity.

Keywords

💡Black holes

Black holes are regions in space where gravity is so strong that nothing, not even light, can escape from it. They are formed from the remnants of massive stars after a supernova explosion. In the video, black holes are central to the discussion of quantum gravity and the nature of space and time. The concept of black holes being the 'key to understanding the Universe' is highlighted by Brian Cox.

💡Event horizon

The event horizon is the boundary around a black hole beyond which nothing can escape its gravitational pull. It is considered the 'point of no return'. The video discusses how the event horizon is a place where our understanding of physics is challenged, and it plays a significant role in the concept of black holes and the information paradox.

💡Quantum theory

Quantum theory, or quantum mechanics, is a fundamental theory in physics that describes nature at the smallest scales of energy levels of atoms and subatomic particles. The video suggests that quantum theory clashes with general relativity when applied to black holes, which leads to the quest for a quantum theory of gravity.

💡General relativity

General relativity is a theory of gravitation proposed by Albert Einstein, which describes gravity not as a force but as a curvature of spacetime caused by mass and energy. The video discusses the conflict between general relativity and quantum mechanics when trying to understand black holes.

💡Singularity

In the context of black holes, a singularity is a point of infinite density where space and time cease to exist. The video mentions the singularity as a central problem in understanding black holes, where traditional theories of space and time break down.

💡Escape velocity

Escape velocity is the minimum speed needed for an object to escape the gravitational attraction of a celestial body without further propulsion. The video script uses the concept of escape velocity to explain the idea of black holes proposed by Mitchell and Laplace.

💡Hawking radiation

Hawking radiation is a theoretical prediction by physicist Stephen Hawking that black holes emit radiation due to quantum effects near the event horizon. This concept is pivotal in the video as it challenges the idea that black holes are eternal and introduces the concept of black holes having a lifespan.

💡Information paradox

The black hole information paradox arises from the apparent loss of information about matter that falls into a black hole, which contradicts the principle that information must be conserved in physical processes. The video discusses how this paradox has been a central question in black hole research.

💡Quantum entanglement

Quantum entanglement is a phenomenon in which the quantum states of two or more objects have to be described with reference to each other, even though the individual objects may be spatially separated. The video suggests that quantum entanglement might be related to the emission of Hawking radiation and the resolution of the information paradox.

💡Penrose diagram

A Penrose diagram is a graphical representation of the spacetime used to visualize the geometry of the universe in general relativity. The video mentions Penrose diagrams in the context of understanding the distorted nature of space and time inside a black hole.

💡Emergent spacetime

Emergent spacetime is a concept in theoretical physics suggesting that space and time are not fundamental but emerge from some more basic, underlying reality. The video discusses this idea as a possible resolution to the paradoxes of black holes and as a step towards a quantum theory of gravity.

Highlights

Black holes may hold the key to a quantum theory of gravity and a deeper understanding of space and time.

The event horizon of a black hole is where physics seems to have full control, yet there's a clash between quantum theory and general relativity.

The unification of quantum theory and general relativity is considered the holy grail of theoretical physics.

Black holes are forcing a deeper understanding of what space and time are.

Brian Cox is a professor of particle physics and author of 'Black Holes: The Key to Understanding the Universe.'

The concept of black holes dates back to the 1780s and 1790s with Mitchell and Laplace's idea of escape velocity.

Escape velocity is the speed needed to escape the gravitational pull of a planet or star.

Mitchell and Laplace speculated about stars so massive that their escape velocity exceeds the speed of light, making them invisible.

A black hole's event horizon is the boundary between the external universe and the interior of the black hole.

The event horizon is also described as a place in space where time stops, according to Einstein's theory of relativity.

The nature of what lies at the center of a black hole, the singularity, is still not understood.

Stephen Hawking's work showed that black holes emit particles, known as Hawking radiation.

Hawking's theory suggests that black holes are not eternal and have a lifetime, eventually returning all that fell in back to the Universe.

The Black Hole Information Paradox questions whether information is conserved in the Universe, even when it falls into a black hole.

Current research suggests that black holes do not erase information from the Universe.

The concept of 'emergent spacetime' suggests that space and time are not fundamental but emerge from quantum entanglement.

Understanding black holes may provide insights into the origin of the Universe and the nature of space and time.

Einstein's philosophy of delving deeper into nature to catch a glimpse of something deeply hidden is echoed in current black hole research.

Transcripts

- Could black holes be the key

to a quantum theory of gravity?

A deeper theory of how reality, of how space and time works?

Black holes are interesting

because we have a place called the 'event horizon'

where we think that we have full control of the physics.

We understand what's happening,

but there is a fundamental clash

between our two basic theories of nature:

both quantum theory and general relativity together.

And the quest to unify those two great pillars

of 20th- and 21st-century physics

into what's often referred to as

'a quantum theory of gravity'

is in some sense the holy grail to theoretical physicists.

So black holes are forcing us

into a deeper understanding of what space and time are.

And in that sense, I think it is fair to say

that black holes are the keys to understanding the Universe.

I'm Brian Cox,

I am a professor of particle physics

at the University of Manchester,

and the Royal Society Professor

for Public Engagement in Science,

and amongst other things

I'm the author of the book,

"Black Holes: The Key to Understanding the Universe."

The idea of black holes goes back a long way actually,

back into the 1780s and 1790s.

There were two physicists, mathematicians,

natural philosophers, whatever you want to call them,

working at the time that had the same idea,

apparently independently of each other.

One was a clergyman called Mitchell

and the other was the great French mathematician, Laplace.

And they were both thinking

in terms of an idea called 'escape velocity.'

The escape velocity is the speed you have to travel

to completely escape the gravitational pull of something,

a planet or a star.

So for the Earth, for example,

the escape velocity from the surface of the Earth

is around eight miles a second.

If you go bigger, you make a bigger, more massive thing,

let's go to a star, for example, like the Sun,

it's somewhere in the region of 400 miles a second.

The escape velocity increases

because the gravitational pull at the surface increases.

What Mitchell and Laplace thought,

and I think it's a very beautiful idea,

is they imagined in their mind's eye,

"Well, can you go bigger?

Can you imagine more and more massive stars,

giant stars such that the gravitational pull

is so large at the surface

that the escape velocity exceeds the speed of light?"

And then you wouldn't be able to see them.

To understand why black holes

cause so many conceptual problems,

it might be worth just describing very, very briefly

what a black hole looks like.

So a black hole, what do you see from the outside?

Well, there's an event horizon surrounding the black hole.

In some sense, it defines the boundary

between the external universe

and the interior of the black hole.

And if you go across the boundary

into the interior of this sphere,

then even if you can travel as fast as the speed of light,

you can't escape the gravitational pull of the black hole.

But another description of the event horizon

which confused people

all the way through the history of black hole research

actually, was the idea that the event horizon

when viewed from the outside

is a place in space where time stops.

And that's a direct prediction

of Einstein's theory of relativity.

From the external perspective,

there is a central problem though

which is still not solved,

which is what lies at the center of a black hole?

You might think of it as an infinitely dense point

to which this massive star collapses.

So what are we picturing?

It's this thing called the 'singularity.'

Actually, it's not right to talk

about the center of a black hole really.

Just even in pure general relativity,

when you look at a nice map of a black hole,

a so-called 'Penrose diagram' named after Roger Penrose,

what you see is that space and time is so distorted,

that in some sense, their roles swap,

the singularity is not really a place in space at all,

it's a moment in time, and actually it's the end of time.

But the nature of that thing was not

and is still not understood,

and for many, many years actually

until quite recently, then people thought,

"Well, there we are,

we have a problem with the singularity.

We don't really have any access to it.

We don't have the conceptual tools to explore it.

So it may remain a mystery for a century to come;

it is not clear what to do.

The great revolution in black hole research

was to notice that actually there are conceptual problems,

not only in this extreme place at the singularity,

whatever that might be, but at the horizon.

What Stephen Hawking showed in a landmark couple of papers

is that if you consider quantum theory, quantum mechanics

in the vicinity of the horizon of a black hole

then you find that they glow,

they produce particles, they have a temperature.

This thing that we've pictured

in Einstein's theory is pure geometry,

just distorted space and time actually emits particles-

it's called Hawking radiation.

And Stephen, in his 1974 paper,

gives this hand-wavy description-

which is kind of a nice way to picture what's happening-

the idea is to zoom in

in the vicinity of the event horizon of a black hole.

You can picture what's happening

as a series of particles

coming in and out of existence all the time,

so-called 'entangled particles.'

And so one of those pairs of particles

is on the inside of the event horizon,

and one is on the outside.

And then it can happen that the one on the outside

instead of merging back with its partner again

can escape into the Universe,

removing energy from the black hole as it goes;

therefore, it's shrinking,

which means that one day it will be gone.

That has profound implications.

So black holes are not eternal prisons,

they have a lifetime.

One day, whatever's in there is returned to the Universe.

The question was,

the central question that was immediately raised

by those calculations is this:

What happened to all the stuff that fell in?

The way I've described it,

the way Einstein's theory describes it,

is somehow that stuff goes to the singularity,

whatever that thing is, the end of time,

the region of space time that's so convoluted and distorted

that we don't understand how to describe it at all-

But then one day the whole thing is gone.

All that's left in the far, far future is Hawking radiation,

those particles that were produced

in the vicinity of the event horizon.

The question is, is it possible

if you could collect all that radiation,

all the Hawking radiation through the whole life

of the black hole-

is it somehow possible in principle

that the information about everything

that fell into the black hole throughout its history

is imprinted in that radiation in the far future?

Is that true or is it not true?

You might say, why did I ask that question?

Seems like a bit of a random question.

It's a very important question.

Information is conserved in the Universe as far as we know.

So every law of nature that we have

says that information is conserved.

So let's say that I take a book

and I set fire to it, I incinerate it,

I destroy it in any way that I can.

In basic fundamental physics,

then it turns out

that if you could collect every piece of that thing

that I detonated or incinerated,

every quantum of radiation, every photon, every particle,

everything, in principle, if I could just collect it all,

then I could reconstruct the thing that I had destroyed.

The problem was black holes,

quantum mechanics, general relativity,

when you put them together

you have this apparent prediction

that these things erase information from the Universe-

this became known as the 'Black hole information paradox.'

It turns out if we fast forward to the present day

and a series of papers are still being written,

so this is still research that's happening as we speak,

but it turns out now that the general view

is that black holes do not erase information

from the Universe.

We now think you could collect all that radiation,

and in principle, put it into some quantum computer

and reconstruct the information

about everything that fell in.

But the implications of that,

that the mechanism by which that happens,

I would say it's profoundly exciting

because it really does seem to be given

as a glimpse of a deeper theory of gravity.

The simple way to say it,

let me say it in in one sentence:

It seems that space and time are not fundamental.

So one view, and I emphasize

that there are other views

where the cutting edge of research now,

but one view is a field

which has become known as 'emergent spacetime.'

And so the idea is that space

and time themselves emerge from what?

From quantum entanglement,

from some kind of smaller parts or pieces.

We don't know what those things are.

We don't know the nature of them

but it does seem that there's a deeper underlying theory

from which space and time emerge.

That is what we call the 'quantum theory of gravity.'

And my view is that

if we're gonna talk about the origin of the Universe,

even ask questions such as did the Universe

have a beginning in time,

which we don't know the answer to,

then it surely seems to me

that we have to understand what space and time are

before we can ask

and have any chance of answering such questions.

And black holes,

it turns out are the objects that we can see,

that we can observe that actually exist in nature

that force us down that route to ask questions,

sharp, well-defined questions actually,

about the nature of space and time themselves.

Einstein said that if you look at nature really carefully

and keep pulling at the intellectual threads

and keep going and just keep delving down

into what nature seems to be trying to tell us,

then if you're lucky and persistent,

you can catch a glimpse of something deeply hidden.

It's beautiful that, isn't it?

A glimpse of something deeply hidden,

which is the deep underlying structure of nature,

the deep underlying structure of reality itself.

And I think it's very beautiful.

No one really knows,

I think it's fair to say, where this is going,

but that hints of something deeply hidden.

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