IB Physics Topic A.5.4 Space-time Diagrams Revision Notes (HL)

IB Physics Topic A.5.4 Space-time Diagrams Revision Notes (HL) | RevisionDojo

Spacetime Diagrams: Visualizing Events

A spacetime diagram is a graphical tool that helps us understand how events are perceived in different reference frames.

The Axes

Time Axis ($ct$): Represents time, scaled by the speed of light ($c$) to ensure both axes have the same units (meters).
Space Axis ($x$): Represents position in space.

Tip

Plotting $ct$ instead of $t$ ensures the axes have the same units, making it easier to interpret worldlines and light cones.

Worldlines: Tracing Paths in Spacetime

Definition

Worldline

A worldline is the path an object traces in spacetime.

Object at Rest: Its worldline is vertical, as its position doesn’t change over time.
Object in Motion: Its worldline is slanted, with the slope indicating its velocity.

Example

A photon’s worldline forms a 45° angle with the axes because it travels at the speed of light.
This angle is a universal feature of light in spacetime diagrams.

Light Cones: Defining Causality

Light cones illustrate the boundaries of causality:

Future Light Cone: Events that can be influenced by a signal from the origin.
Past Light Cone: Events that could have influenced the origin.
Outside the Light Cone: Events that are causally disconnected from the origin.

Note

The light cone’s shape reflects the fact that nothing can travel faster than light.
This constraint defines the limits of cause and effect in spacetime.

Space-Time Diagram Example: Explanation

This spacetime diagram represents the motion of objects in different reference frames, with the horizontal axis ($x$) representing position in kilometers and the vertical axis ($ct$) representing time in kilometers of light-travel distance (since $ct$ is used to maintain consistent units between space and time).

Axes and Scale Interpretation

The horizontal axis ($x$) measures the position of events in space, marked in kilometers.

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IB Physics A.5.4 Space-time Diagrams Notes

Spacetime Diagrams: Visualizing Events

The Axes

Worldlines: Tracing Paths in Spacetime

Light Cones: Defining Causality

Space-Time Diagram Example: Explanation

Axes and Scale Interpretation

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Spacetime Diagrams: Visualizing Events

The Axes

Worldlines: Tracing Paths in Spacetime

Light Cones: Defining Causality

Space-Time Diagram Example: Explanation

Axes and Scale Interpretation

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Topic A - Space, time and motion5 subtopics

Topic B - The particulate nature of matter5 subtopics

Topic C - Wave behaviour5 subtopics

Topic D - Fields4 subtopics

Topic E - Nuclear and quantum physics5 subtopics

IB Physics A.5.4 Space-time Diagrams Notes

Topic A - Space, time and motion5 subtopics

Topic B - The particulate nature of matter5 subtopics

Topic C - Wave behaviour5 subtopics

Topic D - Fields4 subtopics

Topic E - Nuclear and quantum physics5 subtopics

Spacetime Diagrams: Visualizing Events

The Axes

Worldlines: Tracing Paths in Spacetime

Light Cones: Defining Causality

Space-Time Diagram Example: Explanation

Axes and Scale Interpretation

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Spacetime Diagrams: Visualizing Events

The Axes

Worldlines: Tracing Paths in Spacetime

Light Cones: Defining Causality

Space-Time Diagram Example: Explanation

Axes and Scale Interpretation

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Duis aute irure dolor in reprehenderit

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