Light is an incredible traveler, moving at the astonishing speed of about one foot per nanosecond. This means that when you hold your hand a foot away from your face, you’re actually seeing it as it was a nanosecond ago. This fascinating concept applies to everything we observe; everything we see is, in fact, a glimpse into the past. The further away an object is, the older the light we see from it.
Consider the Sun: we don’t see it as it is right now, but as it was about eight minutes ago. Similarly, when we look at Alpha Centauri, the closest star system to us, we see it as it was 4.4 years ago. The Andromeda Galaxy, a staggering 2.5 million light-years away, appears to us as it was millions of years in the past.
With the aid of powerful telescopes, we can observe galaxies whose light has been traveling for over 13 billion years. These galaxies appear to us as they were in a young universe, where gravity was just beginning to shape stars and galaxies. But there’s something even more ancient that we can observe.
If we look far enough, beyond the galaxies, we can see parts of the universe so distant that their light has taken nearly the entire age of the cosmos to reach us. Observing the most distant parts of the cosmos reveals regions so far back in time that they are still in the final stages of the Big Bang. These areas are filled with a dense, turbulent plasma, the fiery remnants of creation.
While we are not the center of the universe, we are at the center of our own perception. As light reaches us from all directions, we find ourselves surrounded by layers of cosmic time, like nesting dolls. Each layer represents a different era, showing the evolution of matter much like geological strata.
The most distant layer of time we can observe is the cosmic microwave background. This light has been traveling since the moment the primordial fire began to cool, enveloping us in every direction. We exist within these shells of cosmic time, with the final layer being the fiery remnants of the universe’s birth.
This exploration of cosmic time and light is inspired by a collaboration with Katie Mack, also known as astrokatie. If you’re curious about how we measure the distances to stars and galaxies, Brilliant.org offers an interactive course on this topic. It covers concepts like trigonometric parallax, standard candles, and supernovae. For a daily dose of science, Brilliant also provides a short problem of the day to challenge your understanding of math and science. You can explore these resources at brilliant.org/minutephysics, with special offers for early sign-ups.
Engage in a simulation that allows you to visualize how light travels across different distances in space. Adjust the distance to various celestial bodies and observe how the time it takes for light to reach us changes. This will help you understand the concept of seeing the past through light.
Create a physical model representing the layers of cosmic time surrounding us. Use different materials to symbolize various eras, from the Big Bang to the present. This hands-on activity will reinforce your understanding of how we perceive different periods in the universe’s history.
Conduct research on the cosmic microwave background and its significance in cosmology. Prepare a presentation to share your findings with your peers, highlighting how this ancient light provides insights into the early universe.
Delve into the methods used to measure astronomical distances, such as trigonometric parallax and standard candles. Participate in a workshop where you apply these techniques to calculate the distance to various stars and galaxies.
Join a discussion forum where you can debate and share perspectives on the implications of observing the universe’s past. Discuss how this understanding influences our perception of time and space, and what it means for our place in the cosmos.
Light – Electromagnetic radiation that is visible to the human eye and is responsible for the sense of sight. – Example sentence: The speed of light in a vacuum is approximately 299,792 kilometers per second, a fundamental constant in physics.
Time – A continuous, measurable quantity in which events occur in a sequence proceeding from the past through the present to the future. – Example sentence: In the theory of relativity, time is relative and can vary depending on the observer’s velocity and gravitational field.
Universe – The totality of known or supposed objects and phenomena throughout space; the cosmos; everything that exists, including all matter and energy. – Example sentence: The Big Bang theory is the prevailing cosmological model explaining the early development of the universe.
Galaxies – Massive, gravitationally bound systems consisting of stars, stellar remnants, interstellar gas, dust, and dark matter. – Example sentence: The Milky Way and Andromeda are two of the most well-known galaxies in our local group.
Gravity – A natural phenomenon by which all things with mass or energy are brought toward one another, including planets, stars, and galaxies. – Example sentence: Gravity is the force that keeps planets in orbit around stars and governs the structure of the universe on a large scale.
Cosmic – Relating to the universe or cosmos, especially as distinct from the Earth. – Example sentence: Cosmic microwave background radiation provides crucial evidence for the Big Bang theory.
Stars – Luminous spheres of plasma held together by their own gravity, undergoing nuclear fusion reactions in their cores. – Example sentence: Stars are born in nebulae and evolve over millions to billions of years, eventually becoming white dwarfs, neutron stars, or black holes.
Plasma – A state of matter consisting of a gas of ions and free electrons, typically found in stars, including the sun. – Example sentence: The sun’s outer layer is composed of plasma, which is responsible for solar flares and other solar phenomena.
Background – The cosmic microwave background is the thermal radiation left over from the time of recombination in Big Bang cosmology. – Example sentence: The discovery of the cosmic microwave background radiation in 1965 provided strong evidence for the Big Bang theory.
Evolution – The process by which different kinds of astronomical objects develop and change over time. – Example sentence: The evolution of stars is a complex process that involves changes in their structure and energy output over time.
