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Time

Before we can discuss awesome things like

time travel and causal loops we need to

determine what time is first

What do you guys think?

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Presentism

Only the present moment exists, the past and

future do not.

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Clarification

Conventionally, time is divided into three distinct regions;the past, the present, and the future. the past is

generally seen as being immutably fixed (i.e. it is totallyunchangeable), and the future as undefined and nebulous(i.e. unclear, vague).

As time passes, the moment that was once the presentbecomes part of the past; and part of the future, in turn,

becomes the new present. In this way time is said to pass, with a distinct present

moment "moving" forward into the future and leaving thepast behind.

What are the implications of this viewpoint for time travel?

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Four-dimensionalism/Eternalism

Future events are "already there",

there is no objective flow of time.

The entire universe is contained

within the block

It is sometimes referred to as the

"Block Time" or "Block Universe"

theory due to its descriptionof space-time as an unchanging

four-dimensional "block"

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Clarification

Eternalism considers all points in time to be

equally valid frames of referenceor equally

"real.

Essentially all moments in time are in existence

we simply do not have access to them.

The concept of the past present and future still

exist but are states of bring and are dependent ofthe direction from which you are observing it.

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The Past Where are you standing relative to this van?

Assume you are stationary.

You are located behind it, you are able to see

it traveling away from you. This is like the past

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The Future Where are you standing relative to this van?

Assume you are stationary.

You are located in front of it, it is coming towards you.This is like the future, it is already in existence and istravelling towards you at a rate of can anyone guess

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One SecondPer

Second

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Time travel

What would a presentist say about time

travel?

What would an eternalist say about time

travel?

What does science say about time travel?

Though the science in fascinating we are focusing

on philosophy here though there is some

support for the eternalist viewpoint.

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Time travel

Let us assume an eternalist perspecitve:

If we do so time travel is possible

I cant waitor perhaps I am already back from the

future and therefore know all the secrets about

the universe

What are some of the problems we now face?

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Problems

How do I age if I go back in time?

What happens to everyone elses time if I go

back to the past or forward into the future?

What happens if I change something in the

past?

Any others.

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Lets start with what happens if I change something

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Causal loops

Before we discuss this problem in a little more

detail lets talk about one of my favorite topics

in all of philosophy

Best explained through an example

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Example

Imagine if no one wrote Motzarts symphonies:

What do you mean you askwell imagine if Mozart was my favorite composerof all time and I really wanted him to sign a copy of my book containing all hissymphonies. So I build a time machine and travel back to see him taking thisbook with me. Now I slightly miscalculate and arrive before he has writteneven one of his pieces, but I ask him to sign them anyway. Unfortunately upon

my return to the time machine I left my book in Mozart's house and as Itraveled back to today my time machine broke so I was not able to go backand collect my book. Now Mozart looked at these symphonies and thought tohimselfwow these are great, he slowly copied and released them over therest of his life.

In essence we have a case where there is no composer of the music. I believe

Mozart wrote it, however there was no creativity in the process, the musicmerely materialized out of this loop.

Who wrote them?

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The Grandfather paradox

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How can we solve this problem

Perhaps as suggested in the clip there are

multiple parallel universe theory

Every time we go back in time we create another universe

in which another reality takes place

Perhaps there is a mysterious additional law of

physics which have not yet uncovered.

Perhaps this in itself proves that time travel isimpossible

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Back to the Grandfather paradox

Is there any resolution?

All we can do really is employ the

same solutions to our causal

loops.

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Could you encounter yourself?

Is it possible that there are 3 versions of

myself in the same room at the same time?.

We normally think of time as consisting of

temporal parts i.e. as having a Continuity

Connectedness Causation

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Personal time

External time exists on a one dimensional plane (it is linear)and continues forward at a constant uninterrupted rate ofone second per second.

Conversely but not in contradiction with the notion ofexternal time is time as experienced by the individual.

This is known as personal time, it is in essence experiential.Though the time traveller will continue to age at the rate ofone second per second, he/she moves through externaltime appearing out of sequence with its ostensible linearity,thus external time is of little consequence whenconsidering his/her physical age and not a limiting factorwhen considering personal time.

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A time traveler seen from the standpoint of an

external observer.

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Cool idea to leave you with

Many years from now, a transgalacticcivilization has discovered time travel. A deep-thinking engineer wonders what would happen

if a time machine were sent back to the

singularity from which the big bang emerged.His calculations yield an interesting result: thesingularity would be destabilized, producing an

explosion resembling the big bang Needlessto say, a time machine was quickly sent on itsway.