Einstein 101: what Einstein 101: what isis space ? space ?

Peter CobboldPeter Cobbold

Ruthin U3ARuthin U3A

28 Feb 201728 Feb 2017

Einstein 101Einstein 101

● “101” an elementary introductory course● 101 years since General Relativity published in

1915● 101 years later – 'what is space' today

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Nothing in this talk is sci-fi

PLAN of TALK ● Newton: fixed space and time.

● Faraday, Maxwell: speed of light is a constant.

● Einstein: time and space are not fixed. Special Relativity 1905, General Relativity 1915

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● Space updated to 2017:

● Quantum Gravity - the big puzzle

● Clues from Black Holes

● Space according to the Holographic Principle:

● Space is 'emergent', not fundamental.

WHAT WHAT ISIS SPACE ? SPACE ?

Space is Space is everywhereeverywhere

● 'Outer space' ● Space we move in● Space inside us

What isis space?

Newton's concept of space in 1687

Newton's fixed space and time are our Newton's fixed space and time are our common sense.common sense.

Einstein showed space and time are not Einstein showed space and time are not fixed. fixed.

Einstein's two theories of Relativity defy Einstein's two theories of Relativity defy our common experience of space and our common experience of space and time............Einstein had a reply......>>time............Einstein had a reply......>>

Einstein's two theories of RelativityEinstein's two theories of Relativity

1905 1905

Special RelativitySpecial Relativity

- effect of motion on - effect of motion on space and timespace and time

1915 1915

General RelativityGeneral Relativity

- effect of mass on - effect of mass on space and timespace and time

Einstein's theories of Relativity have Einstein's theories of Relativity have been confirmed by many measurements.been confirmed by many measurements.

Einstein built upon a mid-1800s discovery in electricity and magnetism.

Einstein had pictures of Michael Faraday and James Clerk Maxwell on his study wall.

Faraday and MaxwellFaraday and Maxwell Faraday provided the experimental measurements of electricity and magnetism, and the concept of electrical and magnetic fields.

● Maxwell formalised these data in e-m field equations. From this he derived a wave equation containing a constant number:constant number: c c

● c was equal to the speed of light● Maxwell had discovered light is an

electromagnetic wave, in the same spectrum as x-rays, radio waves and microwaves

C● c is the speed of light in vacuum

(same for radio, microwaves, X-rays. All are electromagnetic waves)

● 186,000 miles per second● 300,000 km per second● 7 turns around the equator in a second● 671 million mph.● light is a bit slower in air, much slower in glass (120,000

mi/sec)

SPECIAL RELATIVITYSPECIAL RELATIVITYEinstein's postulateEinstein's postulate

'The Constancy of the speed of light'. 'The Constancy of the speed of light'.

The speed of light in empty space is The speed of light in empty space is an absolute constant of nature and is an absolute constant of nature and is

independent of the motion of the independent of the motion of the emitting body.emitting body.

SPECIAL RELATIVITYSPECIAL RELATIVITYEinstein's postulateEinstein's postulate

'The Constancy of the speed of light'. 'The Constancy of the speed of light'.

The speed of light in empty space is The speed of light in empty space is an absolute constant of nature and is an absolute constant of nature and is

independent of the motion of the independent of the motion of the emitting body.emitting body.

Special Relativity: Special Relativity:

Time and space change in concert Time and space change in concert to keep the measured light speed to keep the measured light speed

constantconstantwhatever the relative speed of whatever the relative speed of

observer and observed.observer and observed.

Interactive site: http://www.pbs.org/wgbh/nova/physics/spacetime-trip.html

Thought experiment: we are standing on the roadside and observe a car

driving past us very fast

● The car will be shorter in the direction it is travelling. Its height and width will be unaltered.

● This is NOT an optical illusion. The car is shorter because of 'Length contraction' of space in the direction it is moving. Space in all the car's atoms shortens.

Observer outside cab and car are both stationary:

Car moving relative to observer at 0.8c 536million mph

0.95c 636million mph

99% of light speed

LENGTH CONTRACTIONLENGTH CONTRACTION● The car will be shorter in the direction it is

travelling, its height and width will be unaltered ( ignoring GR).

● This is NOT an optical illusion. The car is shorter because of 'Length contractionLength contraction' of space, including within all its atoms.

● The clock on the car's dashboard will be seen by us to go slower compared with our watch. This is “Time dilationTime dilation”

Special Relativity in a nutshell

Brian Greene on Special RelativityBrian Greene on Special Relativity:

“Time and space are relative. Each of us carries our own clock, our own monitor of the passage of time. Each clock is equally precise, yet when we move relative to one another, these clocks do not agree.

The same is true of distance. Each of us carries our own yardstick, our own monitor of distance in space. Each yardstick is equally precise, yet when we move relative to one another, these yardsticks do not agree.”

(Brian Greene continued)

“If space and time did not behave this way, the speed of light would not be constant and would depend on the observer's state of motion.

Space and time adjust themselves in an exactly compensating manner so that observations of light's speed yield the same result, regardless of the observer's velocity.

This is not dexterous wordplay, sleight of hand, or psychological illusion. This is how the universe works.”

Brian Greene 'Fabric of the Cosmos' ( DVD, youtubes, books)

http://www.pbs.org/wgbh/nova/physics/special-relativity-nutshell.html

Faster than the speed of light ?

Faster than light > negative time > causality paradox.

● There was young lady named BrightThere was young lady named Bright

Who drove far faster than lightWho drove far faster than light

She set off one day, in a relative way,She set off one day, in a relative way,

And arrived the previous nightAnd arrived the previous night

General Relativity General Relativity 19151915

General RelativityGeneral Relativity

""Mass tells space-time how to Mass tells space-time how to curve, and space-time tells curve, and space-time tells mass how to move.mass how to move.""

Einstein replaced Newton's 'force of gravity' Einstein replaced Newton's 'force of gravity' with a geometric concept: curvature of with a geometric concept: curvature of spacetime by matter.spacetime by matter.

Gravity is curved spacetime.Gravity is curved spacetime.

Imagined lines of space converging near mass

Cartoon of mass curving space ( confusing mix of 3D and 2D)

Spacetime Curvature by masseshttps://hardscienceainthard.files.wordpress.com/2016/03/gravitational-gif-0.gif?w=640

Space contracts near mass Space contracts near mass Time flows slower near mass Time flows slower near mass

Eddington 1919: confirmation of General Relativity- starlight displaced by sun's mass

PLAN of TALK ● Newton: fixed space and time.

● Faraday, Maxwell: speed of light is a constant.

● Einstein: time and space are not fixed. Velocity dilates time,shortens length. Gravity is time and space warped by mass.

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● Space updated to 2017:

● Quantum Gravity - the big puzzle

● Clues from black holes

● Space according to the Holographic Principle:

● Space is 'emergent', not fundamental.

Relativity is not the end of the story...Relativity is not the end of the story...

● SR and GR are proven theories with many supporting measurements.

● But Relativity is classical physics. There is no mention in the theories of Relativity of the quantum world of fundamental particles. Yet these particles are the building blocks of nature.

● Einstein tells us nothing about “Quantum Gravity”

We now move on to present day science >>>>>

The quest for a quantum The quest for a quantum theory of gravitytheory of gravity

The quest for Quantum GravityThe quest for Quantum Gravity● Quantum Mechanics dates from the first half of the 20th

Century.

● QM describes the behaviour of the smallest components of nature: atoms, and their fundamental particles such as quarks and gluons; photons; electrons

● Three forces of QM influence the particles: the Electromagnetic Force, the Strong Nuclear Force, and the Weak Nuclear Force,

● Gravity does not appear in the equations Gravity does not appear in the equations of Quantum Mechanicsof Quantum Mechanics

So...how can particles warp space ???

Black holes:Black holes:

Quantum Mechanics meets Quantum Mechanics meets General Relativity and GravityGeneral Relativity and Gravity

Black holes contain enormous amounts of matter Black holes contain enormous amounts of matter ( mass) in a tiny volume. ( mass) in a tiny volume.

So their gravity is So their gravity is extremeextreme

Black holes:Black holes:

Quantum Mechanics meets Quantum Mechanics meets General Relativity and GravityGeneral Relativity and Gravity

Black holes contain enormous amounts of matter Black holes contain enormous amounts of matter ( mass) in a tiny volume. ( mass) in a tiny volume.

So their gravity is So their gravity is extremeextreme

Black holes lead to a new concept of Black holes lead to a new concept of gravity and spacegravity and space

The extreme mass density of a BH bends spacetime such that not even massless photons of light can escape. So black holes are a good place to look for gravity interacting with the quantum world.

● An unexpected outcome is a totally new concept of space and gravity.

Earth would become a black hole if all its mass were collapsed to the size of a grape

● Nothing can exit a black hole once it has fallen through the Event Horizon ( the skin of the grape).

● The surface will be utterly black and a perfect sphere.

Black hole and light

Extreme spacetime curvature by mass prevents anything escaping, including light, once at the event horizon

The story of how Black The story of how Black HolesHoles

led to the led to the 'Holographic Principle', 'Holographic Principle', the dominant concept of the dominant concept of

Space and gravity todaySpace and gravity today

The story begins in 1970s: what happens to matter that falls into a black hole ?

● In 1970s Stephen Hawking showed Black Holes can evaporate, as 'Hawking radiation'. If so, matter and information would be lost.

● But loss of information is absolutely forbidden: matter and its information cannot be destroyed.

● This is the black hole 'Information Paradox'

Paradox resolved:

Jacob Beckenstein and later Gerard t'Hooft and Leonard Susskind proposed that the information of infalling matter remained on the black hole event horizon and could escape the black hole as it evaporated. Information was preserved on the horizon, not lost.

Stephen Hawking

● < Gerard t'Hooft● Nobel 1999

● Leonard Susskind

Jacob Beckenstein >

Leonard Susskind

published 2009 >>

Beckenstein / t'Hooft equation brings together Einstein, Newton and Quantum

Mechanics

The first insight intoThe first insight into

Quantum GravityQuantum Gravity

A quandary:

Information describing matter in an object is captured on the event horizon: matter is preserved.

Yet the object also falls into the black hole:matter is lost.

Doesn't that mean there are two lots of matter??

Susskind >>>>

Paradox: matter falls into a black hole AND its information stays on the event horizon.

'Susskind's duality': Alice and Bob● Alice decides to explore a

black hole by entering it. She falls past the event horizon and notices nothing unusual. Information about Alice cannot be seen by Bob: no messages can get out of a BH.

● Bob stays orbiting the BH at a safe distance. He watches Alice fall towards it. He sees her freeze in time at the event horizon, and go dimmer and redder on the event horizon. Information about Alice is not lost.

Susskind's Duality

Susskind's black hole duality ( Alice and Bob) suggests that information about a physical object can exist both on a 2D surface – the event horizon – and within a 3D space enclosed by the area.

●

Susskind: “The black hole horizon is a “The black hole horizon is a scrambled hologram of everything inside”scrambled hologram of everything inside”

Black Hole information duality Black Hole information duality as a model for the Universe:as a model for the Universe:

The Holographic The Holographic PrinciplePrinciple

Brian Greenehttps://www.wired.com/2012/05/geeks-guide-brian-greene/

● “Over the course of many years,” says Greene, “they developed an idea that when an object falls into a black hole, yes indeed, it falls in, but a copy of all of its information content gets in some sense ‘smeared out’ on the surface of the black hole, on the horizon of the black hole. Smeared out in some sense like a series of 0’s and 1’s, the way information is stored in a typical computer.”

And if three-dimensional objects inside a black hole can be represented by two-dimensional data spread across its surface, the same might be true of our universe as a whole.

Leonard Susskind on the Holographic Leonard Susskind on the Holographic PrinciplePrinciple“the three-dimensional world of ordinary the three-dimensional world of ordinary experience—the universe filled with galaxies, experience—the universe filled with galaxies, stars, planets, houses, boulders, and people—is stars, planets, houses, boulders, and people—is a hologram, an image of reality coded on a a hologram, an image of reality coded on a distant two-dimensional surface. This new law of distant two-dimensional surface. This new law of physics, known as the Holographic Principle, physics, known as the Holographic Principle, asserts that everything inside a region of space asserts that everything inside a region of space can be described by bits of information can be described by bits of information restricted to the boundary.restricted to the boundary.”

What is 'holographic' ?

Photographic Hologram Information recorded in diffracted light on a flat (2D) photographic film can be projected to create a 3D image

● CURI, Glyndwr.ac.uk

The Holographic Principle: the universe as a holographic projection

Susskind on the Holographic Principle● “the three-dimensional world of ordinary the three-dimensional world of ordinary

experience—the universe filled with galaxies, experience—the universe filled with galaxies, stars, planets, houses, boulders, and people—stars, planets, houses, boulders, and people—is a hologram, an image of reality coded on a is a hologram, an image of reality coded on a distant two-dimensional surface. This new law distant two-dimensional surface. This new law of physics, known as the Holographic of physics, known as the Holographic Principle, asserts that everything inside a Principle, asserts that everything inside a region of space can be described by bits of region of space can be described by bits of information restricted to the boundary.information restricted to the boundary.”

Mathematical support for the Holographic Principle

● Juan Maldacena 1997● the most highly cited paper in theoretical physics,

ever.● Provided the first mathematically rigorous

support for the Holographic Principle.● Unintelligible to us, even the title:

“Anti de Sitter / Conformal Field Theory Correspondence “

Maldacena AdS/CFT

The idea is as follows:

A quantum gravity theory in the interior of an anti–de Sitter spacetime is completely equivalent to an ordinary quantum particle theory living on the boundary.

The Holographic PrincipleThe Holographic Principle- Particles and forces on the bound, but no gravity

- Space (the bulk) is a projection with gravity arising from its curvature

https://www.youtube.com/watch?v=XoP0lzBC9mo

Space is 'emergent'

What does 'EMERGENT' mean?

● An example: Temperature is 'emergent'. It is not a fundamental property of particles but an ensemble measure of how fast they are moving.

● Pressure is also 'emergent': it is how close the particles are squeezed together on average.

● Single particles cannot have 'temperature' or 'pressure', neither is a fundamental property.

SPACE is 'SPACE is 'EMERGENTEMERGENT''

According to the Holographic Principle the third dimension of space – which gives it volume – emerges from the interactions between particles and forces acting on a distant 2-dimensional bound beyond the observable universe.

● Gravity is also emergent through 3-D space curving according to particles and forces acting at the 2-D bound, so satisfying General Relativity.

A revolution in physics?A revolution in physics?The Holographic Principle is the dominant The Holographic Principle is the dominant

hypothesis of quantum gravity and space. It hypothesis of quantum gravity and space. It remains to be seen how theories develop. remains to be seen how theories develop.

BUT....BUT....

Thank you

A pdf of the talk complete with further reading will be posted on Ruthin U3A website.

The first observational test of the Holographic The first observational test of the Holographic PrinciplePrinciple

● January 2017. Skenderis et al use HP to describe CMB

● The Cosmic Microwave Background, measured by telescopes, dates back to the Big Bang, 13.7B year ago.

● The quantum pattern in CMB, vastly expanded by “inflation” led to todays' pattern of galaxies across the universe.

“The glue that holds the universe together”

● Particles and information may be correlated across the bulk of the universe from the bound, infinitely fast, by ENTANGLEMENT and WORMHOLES

● Black Holes again provide the clues....

● That means that every particle of Hawking radiation, no matter how far away it is from where it started, is directly connected to a black hole’s interior via a shortcut through spacetime. “Through the wormhole, the distant stuff is not so distant,” Susskind says. (recall Alice and Bob)

Perhaps entanglement links the universe's holographic bound to the bulk.

A revolution in physics?A revolution in physics?The Holographic Principle is the dominant The Holographic Principle is the dominant

hypothesis of quantum gravity and space. It hypothesis of quantum gravity and space. It remains to be seen how theories develop. remains to be seen how theories develop.

BUT....BUT....

Thank you

A pdf of the talk complete with further reading will be posted on Ruthin U3A website.

Further reading● Books written for a general but 'science curious'

audience:● Susskind's 2009 book on slide 50● Lee Smolin “Three roads to quantum gravity”

(2001)

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For beginners, Brian Greene's EXCELLENT youtubes, parts 1 and 3:

Brian Greene youtube, part1 of 4 :

https://www.youtube.com/watch?v=BnmrFrUkBv0

Maldacena (“The illusion of gravity” Sci Amer 2005)

● http://www.sns.ias.edu/~malda/sciam-maldacena-3a.pdf

Beckensteinhttp://www.phys.huji.ac.il/~bekenste/Holographic_Univ.pdf

● Skenderis CMB:

https://phys.org/news/2017-01-reveals-substantial-evidence-holographic-universe.html

● Inaugural lecture:

● https://www.youtube.com/watch?v=XoP0lzBC9mo

● WWW: Wikipaedias are mostly too specialised

● Entanglement:

● http://www.nature.com/polopoly_fs/1.18797!/menu/main/topColumns/topLeftColumn/pdf/527290a.pdf

● https://www.scientificamerican.com/article/tangled-up-in-spacetime/

● https://www.sciencenews.org/article/entanglement-gravitys-long-distance-connection