Einstein and Godel on Time Travel

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Questions and Answers

What do the inner and outer cylinders represent in Godel's model of time travel?

The limits of the universe

Two separate time periods

Different dimensions of space

Two interconnected space-time regions (correct)

What represents the motion of a person traveling through space-time in Godel's model?

A straight line

A zigzag path

A circular pattern

A swirling line (correct)

What happens when the traveller reaches the edge of the inner cylinder?

They disappear into a black hole

They pass into the outer cylinder of space-time (correct)

They stay in the same region indefinitely

They enter an entirely different universe

What does moving anti-clockwise around the outer cylinder represent?

Traveling to a later time Signup and view all the answers

As a traveller moves from point A to point B in the outer region, what temporal effect occurs?

They move backwards in time relative to the inner region Signup and view all the answers

What is the primary factor affecting the warping of space-time according to Einstein's theory?

Massive objects Signup and view all the answers

Which of the following concepts suggests the potential for time travel?

Black holes and worm holes Signup and view all the answers

In Einstein's model, what happens to an object's existence in relation to time?

It can exist and cease at different points in time Signup and view all the answers

What does the curvature of space-time imply about time's progression?

It can loop back on itself Signup and view all the answers

What critical question does the discussion of time travel lead to?

Is it compatible with the laws of nature? Signup and view all the answers

What is the consequence of killing your grandfather as a boy according to the grandfather paradox?

You will never be born. Signup and view all the answers

What can time travelers do to the past according to the grandfather paradox?

Only influence the past as it was. Signup and view all the answers

Why is it impossible to kill grandfather from the perspective of the paradox?

Because it would create illogical contradictions. Signup and view all the answers

What is the primary issue with the traditional view of time travel as described?

It necessitates the existence of paradoxes. Signup and view all the answers

What is a requirement for a time traveler to kill someone in the past successfully?

The person must have already been killed by someone else. Signup and view all the answers

Which concept allows for preventing changes to the original timeline during time travel?

Parallel timelines Signup and view all the answers

What remains an unanswered question raised by the grandfather paradox?

What prevents time travelers from changing the past. Signup and view all the answers

What is the focus of the discussion on time travel as stated?

Traveling to the past of the original timeline Signup and view all the answers

What is the grandfather paradox primarily concerned with?

The possibility of erasing one's existence. Signup and view all the answers

What does the new timeline concept permit in the scenario of time travel?

It prohibits changes to the past. Signup and view all the answers

What does Lewis's theory suggest about the identity of a person over time?

A person consists of different temporal parts. Signup and view all the answers

What is a consequence of applying Leibniz’s Law to time travel identity?

If two versions of a person exist, they must share all properties. Signup and view all the answers

How might one resolve the contradiction of meeting one's younger self while considering them identical?

By defining their properties based on their respective locations. Signup and view all the answers

What metaphor does Lewis use to explain his concept of identity over time?

A road composed of various sections. Signup and view all the answers

What is the suggested issue with considering You25 and You15 as the same person?

They must share all properties including wisdom. Signup and view all the answers

What do causal loops in time travel suggest about the origin of certain events or items?

They indicate that some items or knowledge come from nowhere. Signup and view all the answers

Which view argues that causal loops are merely strange but not impossible?

The perspective that accepts the existence of causal loops as an acceptable consequence. Signup and view all the answers

In the second example of a causal loop involving a time machine, where does the knowledge of how to create the time machine originate?

It seems to come from nowhere. Signup and view all the answers

What is one of the objections to the possibility of time travel related to causal loops?

They create scenarios where events can occur without a source. Signup and view all the answers

According to one of the views discussed, what could prevent time travel from resulting in causal loops?

Time travel must avoid causing changes to the original timeline. Signup and view all the answers

Study Notes

Einstein’s theory of space-time

Einstein believed that the speed of light is constant for all observers
Einstein's theory of general relativity states that space-time can be affected by the mass of objects within it.
Massive objects warp the topography of space-time
The warping of space-time can create black holes and worm holes, making time travel possible.

Godel’s Time Travel Model

Godel demonstrated how time travel is compatible with Einstein's general theory of relativity.
Godel describes time travel by using two cylinders that represent two space-time regions wrapped around one another.
The traveller starts in the inner region of space-time and finishes at an earlier time in the inner region.
The traveller moves from the inner to the outer cylinder and back again

Why Time Travel is Logically Impossible

Some argue that time travel is impossible because it is logically contradictory.
“Second time around” refers to the idea that the traveller can witness an event twice, once without their presence and then again while they are there.
It is contradictory to say that an event happens twice.
Time travellers cannot change the past – if a traveller were to alter a past event, it would be a contradiction.

Summary

Massive objects warp the topography of space-time, according to Einstein’s theory of general relativity.
Godel's model shows how time travel could be achieved, but it is logically impossible, because events can only happen once, even for a time traveller.

Introduction

Time travel does not mean past events happen again.
It does not allow for changing the past.

Parallel Timelines

One conception of time travel allows for creating a new timeline.
Travelling to the past creates a new timeline, branching off from our own.
This does not allow for changing the past in our timeline but only allows for creating a different timeline.

The Grandfather Paradox

The most famous paradox about time travel is the grandfather paradox.
Imagine traveling back in time to kill your grandfather before he became evil.
You cannot kill your grandfather as a boy because it would mean that you, the time traveler, would not have been born.

The Grandfather Paradox: Contradictions

This creates contradictions: 1) you are born and travel back in time, 2) you are never born because your grandfather was killed, 3) your grandfather died peacefully in old age, 4) your grandfather was killed.
Time travelers can kill people in the past but cannot kill anyone who did not die in the past.
This means that you cannot change the past but can influence the past to be what it already is.

Grandfather Paradox Again

The grandfather paradox raises the question of what prevents you from killing your grandfather.
You might be able to kill the boy, having the gun, but you cannot kill him because he lived to be an old man.
No mysterious forces are required, according to Lewis. Ordinary events such as a banana peel, a jammed gun, or losing nerve will prevent you from killing your grandfather.

Improbable Time Travel

Horwich argues that Lewis' view makes time travel highly improbable.
It states that time travel will create a string of unlikely coincidences to prevent changing the past, which makes time travel improbable.

Mysterious Ring-fencing

Others argue that Lewis' view involves an unexplainable ring-fencing of the past, which prevents changing it.
It involves a mysterious force for keeping the past as it already is, which is a concept that is not easily explained.

Causal Loops

Time travel could allow causal loops where effects occur before their causes.
A common example is a time traveler bringing an object from the future, which then influences events that led to their existence.
Such loops create a paradox because the object seems to originate from "nowhere."
An alternative scenario involves someone learning of time travel in the future, returning to the past to teach their younger self, leading to the question of how the knowledge originally came about.
While causal loops might appear impossible, some philosophers argue they are merely "strange" not "impossible."
These loops can be compared to the inexplicable origin of the Big Bang; if we can accept its existence despite lack of explanation, we might do the same for causal loops.

Time Travel and Identity

Time travel introduces challenges to our understanding of personal identity.
The paradox arises when a traveler meets their younger self, potentially possessing different characteristics (e.g., wisdom vs. foolishness).
Identity relies on Leibniz's Law, which states that if two things are identical (e.g., two versions of the same person), they must share all properties. However, this seems contradicted by the time traveler having different properties at different points in their life.

Solutions to the Identity Problem

Lewis's Temporal Parts Theory:
- Suggests that individuals are "space-time worms" spread across time, composed of temporal parts.
- This allows for different temporal parts of the same person to have distinct properties without violating Leibniz's Law.
Relativized Properties:
- Proposes that properties are relative to locations in space-time, not absolute.
- If a traveler is wise in the future but foolish in the past, they possess wisdom at place A (future) and foolishness at place B (past).
- This allows for identical individuals to have seemingly contradictory properties.
Both solutions offer explanations for how identity can maintain within a time travel framework.

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Description

Explore the fascinating theories of time travel as proposed by Einstein and Godel. Understand the concepts of space-time warping, the effects of mass, and the logical contradictions surrounding time travel. This quiz delves into their groundbreaking ideas and implications for the universe.