Does cosmic expansion exceed light's velocity?
In short: The iron law of physics states nothing can travel faster than light. Yet, astronomers observe distant galaxies receding from us at speeds that appear to break this limit. The solution isn't found in the motion of galaxies through space, but in the mysterious behavior of space itself.
To understand this cosmic loophole, one must distinguish between movement through space and the expansion of space itself. The speed of light acts as a local speed limit, preventing objects like rocket ships from accelerating past it within a specific region. Nevertheless, special relativity imposes no equivalent limit on the rate at which vast cosmic gaps can grow. In an expanding universe, galaxies are not necessarily speeding through space; rather, the space between us and those galaxies is growing.
This expansion is uniform but scales with distance. Imagine a stretchy fabric being pulled at its edges: objects close to you move away slowly, but objects far away appear to move much faster because there is more 'stretchy stuff' between you and them to expand. This is why the expansion rate is often expressed as 68 kilometers per second per megaparsec. At this rate, a galaxy 1 megaparsec away recedes at 68 km/s, while one 2 megaparsecs away recedes at 136 km/s.
The point where galaxies begin receding faster than light is known as the Hubble distance, located approximately 13.77 billion light-years away. We can still observe galaxies beyond this boundary because the light we capture today was emitted billions of years ago when those galaxies were much closer to us. As dark energy causes the expansion to accelerate, the universe may eventually appear almost empty, as nearly every galaxy outside our Local Group is pushed beyond our sight.
Opens the Intellect+ feed with this card first. Swipe up for the next one.
Sources
- Summary by Intellect · source: Is the Universe expanding faster than the speed of light?
- Also: How Can the Universe Expand Faster Than the Speed of Light?
- Also: The Universe can outrun light without breaking Einstein’s rules
To cite this card, link to https://intellectplus.co.uk/app/space-is-the-universe-expanding-faster-than-the-speed-of-light.
How we source, check and correct cards: Editorial standards.
General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.
Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?
Related
More in Cosmology · More in Space · Latest · A–Z · All topics
