Space is where things happen, and time is when things happen. We can measure where things are and when things occur, but in modern physics, we realize when and where are actually part of the same question. To understand the universe, we need to replace the concept of three-dimensional space plus time with a single concept: four-dimensional space-time.
We’ll explore and explain space-time in this series of animations. Animations are a useful tool to visualize the concept of space-time. For instance, if we have a character moving from one point to another, we can track their movement and speed through a series of panels. Each panel records the character’s position at a different time, creating a visual representation of their journey through space and time.
By drawing multiple panels and stacking them up like a flip book, we can record the character’s movement. This is how animation, or even movies, work. For instance, if it takes two seconds for the character to get past each fence post, and they’re spaced four meters apart, we can calculate the character’s velocity as two meters per second. We can work this out from the panels without even flipping through them. From the edge of the flip book, we can see all the copies of the fence posts and the character in slightly different positions in each panel.
The edge of this flip book is known as a space-time diagram of the character’s journey through space and time. We call the line that represents the character’s journey their world line. If the character jogs instead of walking, their world line becomes more tilted, indicating they’re moving twice as fast as before. We can tell this without flipping the panels.
In physics, it’s always good to view things from other perspectives. After all, the laws of physics should be the same for everyone. So, let’s rethink our animation and have the camera follow the character as they jog along. This rearrangement of the panels is known as a Galilean transformation, and it lets us analyze physics from someone else’s perspective. In this case, the character’s perspective.
However, this method has its limitations. If you’re a cosmic ray moving at the speed of light, our flip book of your point of view falls apart. To prevent this, we’ll have to glue panels together. Instead of a stack of separate panels, we’ll need a solid block of space-time, which we’ll explore in the next animation.
Draw a series of panels showing a character moving through space and time. Use a notebook or stack of index cards. Each panel should show the character at a different position. Flip through the book to see the character’s journey. This will help you visualize how movement is recorded in space-time.
Using your flip book, measure the distance between two points (like fence posts) and the time it takes for the character to travel between them. Calculate the character’s velocity. This activity will reinforce your understanding of how space and time are related through movement.
On graph paper, plot a space-time diagram of your character’s journey. The x-axis will represent space (distance) and the y-axis will represent time. Draw the world line of your character. This will help you understand how space and time are combined into a single concept.
Redraw your space-time diagram from the perspective of the moving character. This means adjusting the diagram so that the character appears stationary and the world moves around them. This activity will help you understand how different perspectives can change our view of space-time.
Using modeling clay or building blocks, create a 3D model representing a solid block of space-time. Each layer of the block represents a different moment in time. This hands-on activity will help you grasp the concept of space-time as a continuous entity rather than separate panels.
Understanding – the ability to comprehend or grasp the meaning of something – She had a deep understanding of the complex scientific theories.
Space – a continuous area or expanse that is free, available, or unoccupied – The children played in the open space next to the playground.
Time – the indefinite continued progress of existence and events in the past, present, and future regarded as a whole – The clock on the wall indicated that it was time to leave.
Concept – an abstract idea or general notion – The concept of time travel has fascinated people for centuries.
Four-dimensional – involving or relating to a space or system with four dimensions – The artist’s sculpture was a four-dimensional representation of a complex mathematical equation.
Space-time – a four-dimensional continuum comprising three dimensions of space and one dimension of time, forming the fabric of the universe – The theory of general relativity explains the interaction between matter and space-time.
Animation – the process of creating a moving image by displaying a sequence of static images in rapid succession – The animated film captivated audiences of all ages.
Panels – a flat or curved component, typically rectangular, that forms or is set into the surface of a door, wall, or ceiling – The solar panels on the roof generated enough electricity to power the entire building.
Character – the mental and moral qualities distinctive to an individual – She was known for her kind and compassionate character.
Perspective – a particular attitude or way of regarding something; a point of view – From his perspective, the decision seemed like the best course of action.
