What is time?

Dr. Demetrios Matsakis

Masterclock, Inc.

dmatsakis@gmail.com

2

The second has an exact definition

No longer related to the Earth’s rotation

Is this time?

“That coordinate which can be most simply related to the evolution of closed systems”

• Demetrios Matsakis, 1999
• http://www.britannica.com/science/dynamical-time

Another way:

“The value of a coordinate that can be most simply related to a sequential ordering of events”

• Demetrios Matsakis, these days

Quotes and Misquotes

• “If nobody asks, I know what time is. If anyone asks me, then I know it not”
• Saint Thomas Aquinas, 1225-1274
• “Time is nature’s way of making sure everything doesn’t happen at once”
• Prof. John Archibald Wheeler, from bathroom wall
• (Yogi Berra? Woody Allan?)
• “Space is nature’s way of making sure everything doesn’t happen to you”
• Also John Wheeler/Yogi Berra/Woody Allan/Bathroom

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Newtonian Mechanics

• Time flows evenly throughout the universe
• Always has and always will
• And by the way, I invented calculus

5

Isaac Newton: 1643-1727

Picture from Wikipedia

Gottfried Wilhelm Leibniz: 1646-1716

Time is Relative

• Otherwise, why did God create the universe in 4004 BC?
• And by the way, I invented calculus too
• And my version is better than yours

Picture from Wikipedia

Newton’s Theory of Light

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Light picture from ww.learnnext.com/nextgurukul/wiki/concept/Karnataka/IX/Physics/Newton-s-and-Huygens--Theories.htm

Robert Hooke (1635-1703) thought it was a wave

Hooke picture from https://en.wikipedia.org/wiki/Robert_Hooke

Nature, and Nature’s Laws lay hid in Night

God said, Let Newton be!

And all was light.

- Alexander Pope

1688-1744

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But science progressed

• In 1861, Maxwell showed that light was waves
• Changing electric fields make magnetic fields (electromagnets)
• Changing magnetic fields make electric fields (electric generators)
• Changing electric and magnetic fields will switch back and forth indefinitely
• Making light waves
• The math correctly predicts the speed of light!
• BUT if it is a wave, there must be an ocean (aether)

9

http://fab.cba.mit.edu/classes/862.06/students/alki/GA.html

Michelson-Morley Experiment 1887

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What was the velocity of the Earth with respect to the aether?

The answer is zero! (Nobel Prize, 1907)

Photo by Demetrios Matsakis; painting at US Naval Observatory

Einstein tried to imagine …

• What would a light wave look like if you were traveling alongside it, at the speed of light?
• It would look stationary
• Electric Field would not be changing
• Magnetic Field would not be changing
• How could electric fields be turning into magnetic fields and back again?

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http://fab.cba.mit.edu/classes/862.06/students/alki/GA.html

• Matter can not travel at the speed of light
• Nothing can go faster than light
• All observers will measure identical values for the speed of light.
• No matter how fast or in what direction they are moving

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Special Theory of Relativity, 1905

Therefore,

• Time and Space get mixed up
• Honorable observers will disagree about
• What is stationary
• How long length is
• What is simultaneous
• i.e. what came first
• How fast time moves
• But any physics freshman can calculate what different observers will observe

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Source: http://www.crystalinks.com

/bikeinstein.jpg

And the freshman says:

A stationary observer will think a moving observer’s

• Yardstick shrinks
• Mass is greater
• E=mc²

• TIME RUNS SLOW
• Clocks run slow

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Hafele-Keating experiment, 1971

Nothing can go faster than light?

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Source: http://win_corduan.tripod.com/physics.html

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Time = Causality

• Events are the same for everybody
• My talking to you is an event
• Observers can assign them coordinates in space, and in time
• They can be different
• If light had time to travel from Event A to Event B
• Event A can influence event B
• All observers will agree about which event was first
• Some will think they happened at the same place
• If light did not have time to go from Event A to Event B
• Event A cannot influence Event B
• Observers will disagree about which was first
• None will think they happened at the same place
• TIME ORDER IS INSEPARABLE FROM CAUSALITY

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Causality Example

• Which event happened first?
• Event 1: Albert Einstein awarded Nobel Prize in Stockholm
• On December 10, 1922, Greenwich Mean Time
• Event 2: Supernova 1987A explodes in Large Magellanic Cloud
• It took light 200,000 Earth-years to reach us
• Seen on Earth on February 24, 1987, Greenwich Mean Time (UTC)

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Source:http://www.nobelprize.org/nobel_prizes/

physics/laureates/1921/einstein-facts.html

Source: https://en.wikipedia.org/wiki/SN_1987A#/media/F

ile:Composite_image_of_Supernova_1987A.jpg

But all observers would agree that Earthlings saw Supernova 1987 AFTER Einstein got the Nobel Prize

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Time-order is inseparable from causality

Gravity and Time

• How can gravity pass through empty space?
• How can the Earth pull on an apple?
• How can it pull on the Moon?
• Answer: the General Theory of Relativity (1915)

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Source: http://csep10.phys.utk.edu/

astr161/lect/history/newtongrav.html

Source: https://en.wikipedia.org/wiki/Moon

Special Theory of Relativity & Flat Space�

• Euclidian geometry applies
• Sum of the angles of a triangle are 180 degrees
• Straight line = shortest distance between two points
• Light moves in straight lines
• Matter moves in straight lines
• Unless accelerated by a force
• Gravity is just a force, like electricity

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Source: http://www.wikiwand.com/en/Euclidean_geometry

Curved Space

• Imagine a 2-dimensional ant walking around a sphere
• She is going in a circle
• She thinks gravity brought her back
• You and Einstein realize that her space was curved.

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• Euclidian geometry does not apply
• Plane geometry does not work on a sphere
• Things move straightest way possible
• Principle of Least Action
• Law of Cosmic Laziness

Source: Wikiedia

Ant on globe from http://cosmology.carnegiescience.edu/https@cosmology.carnegiescience.edu/sites/cosmology.ciw.edu/files/images/ball1.png

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Worm Hole

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Imagine these to be the 4-dimensions of space-time as seen from the fifth dimension

Source: http://beforeitsnews.com/power-elite/2013/08/rh-negs-the-universe-has-the-ability-to-change-our-dna-dna-produces-wormholes-in-space-much-more-2442944.html

Black Hole

Is entropy (randomness) time?

Entropy source: http://www.michelecoscia.com/?p=1041

Maxwell’s demon Sources

http://pespmc1.vub.ac.be/ENTROBOX.htmlfro

http://www.clipartpanda.com/categories/devil-20clipart

Ludwig Boltzmann

1844-1906

Does Time have a unique direction?

Smiling lady: www.nursinghomecare.ie 

Baby picture: www.motherandchild.co.uk

Middle-aged woman from https://thepressharold.files.wordpress.com/2014/09/smiling-middle-aged-woman.jpg

Does Time have a unique direction?

Smiling lady: www.nursinghomecare.ie 

Baby picture: www.motherandchild.co.uk

Middle-aged woman from https://thepressharold.files.wordpress.com/2014/09/smiling-middle-aged-woman.jpg

Metaphysical Time

http://www.mandalabooks.com/Metaphysics-and-the-Supernatural

Antiparticles

• Every elementary particle has an antiparticle
• Proton has anti-proton
• Electron has anti-electron
• Hydrogen (electron+proton) has anti-hydrogen
• They have opposite electrical charges
• They accelerate in opposite directions
• When they meet, they annihilate each other and create light (gamma-ray)
• We see this all the time at Fermilab

Are antiparticles time-reversed particles?

• Feynman speculated as much

Sexy Time Travel is time travel for you, but nobody else

^-

• All electrons/particles could be doing this

Does Relativity Enable Time-Travel?

Source: http://www.bloomberg.com/news/articles/2012-04-19/the-deloreans-time-leap

Tachyons

• Very unusual particles
• Can only travel faster than light
• Allowed by equations of special relativity
• Imaginary mass, as √-1
• They go faster as they lose energy
• Can they be used to communicate with the past?
• Emitting a tachyon looks like absorbing an anti-tachyon

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Source: http://spinoff.comicbookresources.com/2015/03/05/

tv-legends-revealed-spock-was-originally-supposed-to-have-red-skin/

• Not observed yet
• Yes, we have looked

Time Travel = Closed Time-like Curves

Source: http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/

time_travel_universes/index.html

Source: http://www.mcescher.com/gallery/back-in-holland/relativity/

Gödel and Einstein, ~1949

Wiggling Worm Holes

• Recipe
• Create wiggling worm hole
• Wait a bit
• Cross to the other end, get off
• Let it wiggle
• Get back on, go back
• Return home before you left

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Sagan picture :http://www.csicop.org/specialcollections/show/carl_sagan_collection

Thorne picture: http://www.orlandosentinel.com/entertainment/

music/strike-a-chord/os-jtutten-hans-zimmer-kip-thorne-

orlando-20160407-column.html

• Possible for time-travel
• Kip Thorne’s response to question by Carl Sagan
• Used by Jodie Foster in movie “Contact”

Grandfather Paradox

You go back and kill your grandfather ten years before your father was born => no father & no you

Stephen Hawking: Chronology Protection Conjecture

If you pass an idea to your past self,� is it still your invention?

Time

If you pass an idea to your past self,� is it still your invention?

Time

Quantum Mechanics & Complementarity

Source: https://stickmenwithmartinis.files.wordpress.com/2012/04/uncertainty-principle.jpg. Portraits from Wikipedia

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You can not know both position and momentum (velocity) to any accuracy

product of their uncertainties > Plank’s Constant 6 10^-26

i.e. position is complementary to momentum/velocity

Ditto for energy and time (lifetime) of a particle

Questioner: What is complementary to truth?

Bohr: Clarity

Niels Bohr

1885-1962

Werner Heisenberg

1901-1976

Quantum Unpredictability

Source: http://frontporchdenver.com/the-fate-of-the-flip/

• There is no way to predict an outcome to 100% accuracy
• You can compute the probability of an outcome
• It is always < 100% and >0
• It may be 99.999999999999%

Is unpredictability just ignorance?

Source: http://endeavoracademy.com/journal/the-universe-and-albert-einstein

Physical properties do not exist until they are measured

The Multiverse and �Shrodinger’s Cat Paradox

Source: http://abhishekk101.blogspot.com/2012/12/schrodingers-cat-paradox-for-dummies.html

50%

50%

Time

Does every possible “now” exist?

Did I lecture you wisely,

like Socrates of Athens in 399 BC?

Or did you try to burn me at the stake,

like Giordano Bruno in 1600?

Quantum calculations require you sum over all possibilities

(Richard P. Feynman, 1918-1988)

Socrates by Jacques-Louis David

Bruno from https://redeeminggod.com/burned-at-the-stake/

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Do time and space just impose order on the infinite set of possible “Now’s”?

• Event = atomic particles in proximity
• Each event is slightly different
• Order them so difference between consecutive events is minimized
• That order is space-time

Source: http://www.clker.com/clipart-jigsaw-puzzle.html

Time = proximity of “nows”?

“Nude Descending a Staircase”, 1912, by Marcel Duchamp via PD-US, https://en.wikipedia.org/w/index.php?curid=3922548

Virtual Particles

Cassimir Effect: http://www.nature.com/news/a-vacuum-can-yield-flashes-of-light-1.12430

They come out of nothing

They quickly disappear

They temporarily violate energy conservation

The larger their energy the quicker they disappear

We have detected their presence

The Quantum Foam

Quantum foam from https://www.pinterest.com/aaronbrady/quantum-of-understanding/

The Plank Scale

Size: 10^-35 meters

Duration: 10^-44 seconds

Mass: 2 10^-8 kgm

Energy: 2 10^-19 Gev

Are Space and Time�Accidents of Nature?

• The color of an object is not a fundamental property.
• Color just depends upon what wavelengths of light the object happens to reflect.
• Music is not a fundamental property of sound
• In the same way, time and space are not fundamental physical quantities.
• In black holes and the quantum foam, space and time can have no meaning.

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- Prof. J.A. Wheeler

Princeton University

43

When did Time start?

• Infinitely back in the past?
• At the Big Bang?
• When 2 multi-dimensional branes collided?
• Or are we somebody’s science experiment?
• Just now?

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Painting by Michelangelo

When will Time end?

• Never?
• When the universe collapses upon itself?
• When 2 multi-dimensional branes separate, ripping the fabric of space-time?
• With a whimper
• as the universe expands to a dilute gas?

Credit: Nicolle R. Fuller/Science Photo Library

The Big Bang

The outcome with highest probability

• Space will expand faster and faster
• In a google of years (1 google = 10¹⁰⁰)
• We will lose contact with our neighbors
1. Light from other galaxies won’t make it
2. Light from other stars won’t make it
• Everything will have decayed: from black holes to protons
• The observable universe will be dilute gas, swirling
• Termed “heat death”, it will actually be extremely cold
• No way to measure time => No way to have time

Immortality in a universe 10¹⁰⁰ years old

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Freeman Dyson

1923-2020

• Our minds must be mapped into whatever kind of matter exist
• As in many science fiction plots
• Define life as the ability to think thoughts
• Those thoughts can be used to control avatars
• Thinking takes energy and must release that as heat
• Brain-equivalents must always be hotter than universe at large
• Cooler brain-equivalents can think slower but more efficiently
• With a given amount of energy, brain-equivalents can:
1. Think and use thoughts to control avatars
2. Shut down until the universe cools enough to accept the waste heat
• Something like hibernating
3. Restart and go back to step 1
• The cycles will take longer and longer
• But the number of thoughts and actions will be infinite
• Does not work in accelerating universe though

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Science to the rescue?

• Most likely does not mean very likely
• Wrong physics
• New physics
• Mutable physics
• Higgs field spontaneously resets from current value of 256

=> 42?

• My favorite: Linde’s theory of baby universes
• Super-engineering
• Find a way to reverse the expansion
• Contact other parts of multiverse

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Time’s Up

Source: http://www.dogoilpress.com/FDS-552996.html