If light were infinite, we could never see our own history
In short: The universe has a speed limit, but why? It isn't just a cosmic rule of thumb; it is the foundation of cause and effect. If light moved instantly, the very concepts of 'before' and 'after' would dissolve into a chaotic present.
The finite speed of light is dictated by two fundamental properties of space: vacuum permittivity and permeability. These constants represent the physical resistance that space offers to the propagation of electromagnetic waves. Because space possesses this inherent resistance, light cannot travel at infinite speeds. If these properties were lower or nonexistent, light would move faster—or potentially instantaneously—but our current understanding lacks a theory to explain why these specific values exist.
A universe with an infinite speed of light would destroy the principle of locality, which dictates that objects are only directly influenced by their immediate surroundings. Currently, because information cannot travel instantly, we are shielded from distant events. If it were infinite, an event anywhere in the cosmos—such as a million hypernovae occurring at once—would affect every other point simultaneously. This would also break causality; Einstein’s Special Relativity ensures that if one observer sees A cause B, all observers agree on that order because information cannot travel backward in time. With infinite speed, different observers could not agree on the sequence of events.
Visually and physically, such a universe would be unrecognizable. We would see the universe exactly as it exists in the current moment, with no redshift and no Cosmic Microwave Background radiation. The night sky would be fully illuminated by every star in existence simultaneously. Furthermore, if the equation E=mc² held true, an infinite speed of light (C) would mean that mass could never be created from energy, as the energy required to produce any amount of matter would become infinite.
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Sources
- Summary by Intellect · source: Why isn't the speed of light infinite? What if it were?
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