Time Travel

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Time Travel

• L1 Introduction to Time and Time Travel

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Apologies

• This lecture owes a lot to youtube.com
• Visuals are very useful when trying to understand
  4-dimensions

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Afraid of the Dark?

• Who remembers trying to race against light so you
  could get in bed before it got dark?
• Turned out light was really fast
• If only we had a time machine

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Proof of Time Travel

• Theoretically, the indeterminacy of sub-atomic
  particles could create very strange effects on
  our level
• possibly including effects that could allow
  time travel
• and heres the proof!

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Einsteins Great Idea

• The speed of light is constant(ly very fast)
• If we had very fast spaceships, this would allow
  us to observe some crazy things
• For example
• The twin paradox
• But we dont need a spaceship
• A regular passenger jet will do
• Or even just a tower! (Visual explanation)

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Backwards Time Travel

• Going forward in time is (relatively) easy
• Going back is much harder
• But Einsteins theory of general relativity seems
  to allow it
• It depends just how much space-time can curve

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Making a Worm Hole

• Black holes warp space-time a lot because of
  their intense mass
• Flying a spaceship through one would be pretty
  risky
• And, who knows where it would take you even if
  you could make it through
• But, there may be a more convenient way

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Dr Ronald Mallett

• Mallett thinks that light can warp space-time too
• Hes currently trying to get funding to see if
  his time machine will work
• Previous video
• Coffee analogy

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Possibilities for Backwards Time Travel

• Malletts light machine
• A naturally occurring closed time-like loop in
  space-time
• A visiting alien race with a time machine on
  board their ship

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Being Specific about Time Travel

• Actually going to the future or past
• Not just some replica of it
• Its all relative
• For me to time travel, there would need to be a
  difference between the speed time passes for me
  and the speed time passes for someone or everyone
  else

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What is Forward Time Travel?

• Forward time travel my time goes slower than
  yours (like aging slower than everyone else)
• My time goes slower than yours as my speed
  increases (relative to yours) and/or if I am
  closer to mass than you (and if that mass
  increases)

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What is Backwards Time Travel?

• What to me, it seems like your time is reversing
  into our shared past
• How space-time (where I am) is warped so
  significantly that it creates a closed time-like
  loop or wormhole to our shared past
• The loop allows me to travel faster than the
  speed of light (not absolutely, but relative to
  our past as we know it or you watching me go
  through it)

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A Closed Time-Like Loop
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This is not a Physics Course

• Dont worry if thats confusing
• the exam question will be based on the logical
  paradoxes of time travel
• Any questions on what time travel is?
• (Not how to do it on a student budget!)

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Take-Home Lessons

• Time is not like what it seems
• If you have an assignment to do, you should do it
  on the top floor of the library instead of the
  bottom because youll work faster! (As long as
  you can get there and back quickly)
• To stay young-looking compared to your friends,
  make sure you take more long-haul flights than
  them!

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Next Time

• Read
• The Case of Jocasta Jones p207
• By Jonathan Harrison
• Get ready to discuss
• Some logical paradoxes of time travel

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Time Travel

• L2 The (Easy) Paradoxes of Time Travel

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Time Travel is Possible!!!

• This might be a hoax, but time travel really is
  possible
• In fact, many of us have already done it

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What is Time Travel Again?

• Actually going to the future or past
• Not just some replica of it
• Its all relative
• For me to time travel, there would need to be a
  difference between the speed time passes for me
  and the speed time passes for someone or everyone
  else

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What is Forward Time Travel?

• Forward time travel my time goes slower than
  yours (like aging slower than everyone else)
• My time goes slower than yours as my speed
  increases (relative to yours) and/or if I am
  closer to mass than you (and if that mass
  increases)

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What is Backwards Time Travel?

• What to me, it seems like your time is reversing
  into our shared past
• How space-time (where I am) is warped so
  significantly that it creates a closed time-like
  loop or wormhole to our shared past
• The loop allows me to travel faster than the
  speed of light (not absolutely, but relative to
  our past as we know it or you watching me go
  through it)

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A Closed Time-Like Loop
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This is not a Physics Course

• Dont worry if thats confusing
• the exam question will be based on the logical
  paradoxes of time travel
• Any questions on what time travel is?
• (Not how to do it on a student budget!)

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The Case of Jocasta Jones

• Follow the story and keep your eye out for
• Weird happenings
• Illegal acts

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The Case of Jocasta Jones
Jocastas 2000
Jocastas 2019
Jocastas 2001
Jocastas 1900?
Jocastas 1910?
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Fathering Yourself is Impossible

• How is it possible for someone to be their own
  father??

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Fathering Yourself is Backwards Causation

• To father yourself, you would have to procreate
  with your mother, but that probably requires a
  few shots and backwards causation doesnt it?
• Surely it would be causing a change in the past,
  which is impossible!
• The past has already happened, so how can we
  change it?

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Backwards Causation

• We normally think of effects as following their
  cause
• Study (usually) causes the effect of a good grade
• The history of Europe has caused the borders
  between nations to be recognised as they are
  today
• But, if you father yourself then the effect of
  that procreation is also the cause!
• Like getting a good grade causing you to have
  already studied!

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The No Destination Objection

• If you havent thought through all of the
  implications of 4-D space-time, then you may
  still believe
• That the past no longer exists
• That the future doesnt exist yet
• That only the present time exists
• If these points are true, then time travel is
  impossible because there is no other time to
  travel to

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Reply to the No Destination Objection

• 4-Dimensional space-time
• It only seems like the past and future dont
  exist because we are not aware of them
• We the event that is our consciousness at this
  current time and place in 4-D space-time
• 4-Dimensional space-time is widely accepted in
  physics and
• Einstein came up with it

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Time Discrepancy Paradoxes

• If you missed the first lecture, you may still
  believe
• That time or the passage of time is a constant
• That time passes the same for everyone and
  everything everywhere
• That Newtonian or absolute time exists
• If these points were true, then time travel is
  impossible because it involves differences in how
  time passes between the time traveller and
  everyone else

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Reply to the Time Discrepancy Paradoxes

• 4-Dimensional space-time
• It turns out that time (and the spatial
  dimensions) are relative
• Time is not fixed or absolute or constant
• The speed of light is constant, but time is
  relative to speed and proximity to mass
• Physicists have proven this and
• Einstein came up with it

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The In Two Places at Once Paradox

• No one person can wholly be in two places at once
• Wholly is important here
• If you believe this, (which you should) then
  doesnt that mean time travel is impossible?
• (because it would allow you to go and wish
  yourself many happy returns at your last birthday
  party)

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Reply to the In Two Places at Once Paradox

• Big spatial objects have different parts that
  make up its whole.- e.g. the North Island
• But, despite what Aucklanders think, the North
  Island is never wholly located in one part
• All objects are really spatio-temporal objects
• In this moment, I am not the whole of me
• Right now I am just a spatio-temporal part of the
  whole that is me throughout space-time
• Just like tectonic plates (different parts of the
  earths crust) can rub against each other, Its
  possible for me(present part) to shake my(past
  part) own hand at my last birthday

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Visiting Myself
My last birthday party
Me existing through space-time
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Take-Home Lessons

• If you time travel into the past, avoid your
  parents at all costs
• Newton was very smart, but he was wrong time is
  not a constant
• The past exists and part of us (and parts our
  parents) currently exist in the past
• So, assuming your parents had at least one cool
  moment in their lives, they are, in a way, still
  partly cool

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Next Time ( Exam Tip!!!!)

• Read
• The Paradoxes of Time Travel p208
• By Ken Perszyk Nick Smith
• Get ready to attempt to solve the logical
  paradoxes of time travel, including the
  Grandfather Paradox which will be very useful
  to know for the exam

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Time Travel

• L3 The (Hard) Paradoxes of Time Travel

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Time Travel is Possible!!!

• John Titor came from the
• future and provided truth
• (available on youtube and
• at www.johntitor.com)
• This might be a hoax, but is backwards time
  travel really possible?
• Physicists say that it is but what about the
  logical contradictions that would result?

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The Paradox of Changing the Past

• If you could go back in time, you could do more
  study for the test and get a better mark
• But, you already have a mark! You cant change
  it its part of history now!
• P1) If time travel is possible, then you could
  change the past
• P2) It is never possible to change the past
• C) Therefore, time travel must not be possible

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Replying to the Paradox of Changing the Past

• Denying P1 Time travel is possible, but it does
  not and cannot change the past
• When you time travel, you create a new alternate
  universe
• So you can change things, but not things from the
  past in our universe
• When you time travel, you can affect the past
  because you already did
• You dont change history you had already
  affected it!
• An accurate history book would already have a
  record of you being there!

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Telling Myself to Study
When I should have been studying
Me existing through space-time
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The Case of Jocasta Jones
Jocastas 2000
Jocastas 2019
Jocastas 2001
Jocastas 1900?
Jocastas 1910?
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Jocastas Son/Husbands Lifeline
Jocasta is born
1980
2000
2019
1900
1910
Jocasta
The guy
The guy is born
The guy dies
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The Grandfather Paradox

• If you could go back in time, you could kill your
  grandfather before he could produce any offspring
• But, if you did that, then there would have been
  no you to make a time machine and go and kill
  him!
• Which means that you cant have killed him

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The Grandfather Paradox (Cont.)

• P1) If time travel is possible, then you could
  kill your grandfather (before he had kids)
• P2) It is impossible for you to have existed if
  you succeed in killing your grandfather (before
  he had kids)
• C) Therefore, time travel must not be possible

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Replying to the Grandfather Paradox 1

• Denying P1 Time travel is possible, but you do
  not and cannot kill your grandfather
• When you time travel, you create a new alternate
  universe
• So you can kill some old guy but its not your
  grandfather (not from your past)
• But does time travelling to an alternate universe
  really count?
• Is it time travel or inter-universal travel?
• For time travel to be meaningful does it have to
  be to our own past?

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Replying to the Grandfather Paradox 2

• Denying P1 Time travel is possible, but you do
  not and cannot kill your grandfather
• When you time travel, you can affect the past,
  but only because you already did
• This works in the Jocasta Jones case, but
• This justification doesnt work this time
• E.g. If you had already been there and killed
  your grandfather then you would never have
  existed

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Replying to the Grandfather Paradox 3

• Denying P1 Time travel is possible, but you do
  not and cannot kill your grandfather
• When you time travel, you can attempt to kill
  your grandfather, but you will never succeed

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Replying to the Grandfather Paradox 3

• Denying P1 Time travel is possible, but you do
  not and cannot kill your grandfather
• When you time travel, you can attempt to kill
  your grandfather, but you will never succeed
• It doesnt have to be magic or Time Guardians
  that prevents the impossible from happening
• Because its impossible to kill your grandfather
  its necessarily true that you didnt kill him
• (however that came about)

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OK Fine, but where are the Time Travellers, then?

• P1) If time travel ever becomes possible in the
  future, then time travellers would most likely
  have visited our past already
• P2) But there is no evidence of time travellers
  in our past
• P3) It is very unlikely that the time travellers
  could have left no evidence
• C) Therefore, its very unlikely that time
  travel ever becomes possible

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Replying to the No Evidence of Time Travellers
Problem 1

• Accept the argument
• Its true that there are no time travellers but
  only because
• Global warming, or
• Nuclear war, or
• Super-viruses, or
• The robotic uprising of the (very) late nineties
• killed off all of the humans before we got
  around to making time machines!

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Replying to the No Evidence of Time Travellers
Problem 2

• Denying P2 There is evidence of time travellers!
• John Titor www.johntitor.com
• That guy who went under his sink (Hakan
  Nordkvist)
• www.youtube.com/watch?vE2sp-clMk8sfeaturerelate
  d
• That mullet guy

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Replying to the No Evidence of Time Travellers
Problem 3

• Denying P1 Only when time travel becomes
  possible (by a human creating and turning on a
  time machine a closed time-like loop) would we
  expect to start seeing things appear from the
  future (recall what Dr. Mallett said)
• So, we wont expect to see anything until the
  first closed time-like loop is set up

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Replying to the No Evidence of Time Travellers
Problem 3

• But what about naturally occurring closed
  time-like loops?
• If these exist in the future, then they could be
  used to travel to our past
• Sure they could but they would have to
  conveniently connect the right two
  location-moments in space-time
• This is just like aliens possibly existing
• They may just be too far away in space-time for
  us to ever meet

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Take-Home Lessons

• Time travel in movies is usually illogical, but
• Time travel is theoretically and logically
  possible in real life
• But if you have homicidal intentions towards your
  ancestors
• then make sure that you look out for banana
  skins

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How to Find out More

• Want to know more about time, time travel and how
  they impact on other topics from this course
  (like free will)?
• Enroll in the metaphysics course next year (or
  the year after) PHIL225/325
• Keep up with the latest science news
• C.E.R.Ns L.H.C. (Large Hadron Collider)
• http//lhc.web.cern.ch/lhc/
• Dr. Ronald Mallet (real time machine maker)
• http//www.physics.uconn.edu/mallett/main/main.ht
  m

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Next Week
The Meaning of Life