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Brian Cox Reveals The Biggest Mystery In Physics
TL;DR
Scientists estimate the universe is 13.8 billion years old, but fundamental questions about the true origin of the cosmos and the nature of time remain unresolved.
KEY POINTS
Estimated age of the universe
Measurements of cosmic radiation indicate the universe was in a hot, dense state about 13.8 billion years ago. This figure comes from observing ancient light that has traveled across space since the early universe, offering a snapshot of its infancy.
What the Big Bang represents
The Big Bang describes a period when the universe was extremely hot and dense, composed mostly of hydrogen and helium with no stars or galaxies. It marks the earliest point scientists can reliably model, rather than a confirmed absolute beginning of existence.
Einstein’s theory and cosmic origins
Albert Einstein’s general relativity, developed in 1915, allows physicists to trace the universe backward in time to a possible “singularity,” where everything converges. However, the theory is incomplete and breaks down under such extreme conditions.
Georges Lemaître’s early insight
Physicist and priest Georges Lemaître proposed in the 1920s that the universe had a beginning, describing it as “a day without a yesterday.” His idea initially met resistance, including skepticism from Einstein himself.
Limits of current physics
Modern physics cannot fully explain what happened at or before the earliest observable moment. The equations suggest a beginning, but they cannot yet describe it with certainty, leaving open the possibility that the Big Bang was not the ultimate origin.
The unresolved mystery of time
A central obstacle is that science still lacks a complete understanding of time itself. Without knowing what time fundamentally is, determining whether the universe truly had a beginning—or what “before” might mean—remains an open question.
CONCLUSION
While the age of the observable universe is well established, the deeper question of its true beginning is still unsettled, highlighting major gaps in humanity’s understanding of time and cosmic origins.
Full transcript
Science has managed [music] to calculate the age of the universe, but there's a frightening detail. We still don't know what time is. >> How How old is the universe? >> 13.8 billion years. We do know that. Well, ah, but the the the the the proper answer is probably should be we don't know. We know that the universe was hot and dense, which we call the Big Bang, 13.8 billion years ago. So, we measured that. Whether that's the origin of the universe is an open question. >> I can cuz I remember it from school, but can a bit and from the TV show, but can you explain to me the Big Bang Theory in the simplest terms? >> Yeah, so um so, actually it was predict not quite predicted, but it's it's Einstein's theory of gravity called general relativity 1915. Yeah. Not long after that, the theory was applied to a universe, so you can kind of model a universe with it. And there was a suggestion that it could be the the case that there's a point in the past when everything's on top of each other, really. So, you So, you can wind back time and it looks like this thing, and it can be called a singularity in the theory or whatever it is. But so, it looks like there might be a beginning. And that was actually primarily a physicist called Georges Lemaître, who's a a priest as well as a physicist and a mathematician in the 1920s, and he famously said to Einstein, "Your theory suggests there was a day without a yesterday." Which is a a beautiful thing. And Einstein actually very famously said back to him, "Your mathematics is excellent, but your physics is not." >> Yeah. >> Because Einstein didn't like this idea initially of a beginning. What does it mean to have a beginning to everything? And the answer is we don't know, but but his theory suggests it. But Einstein's theory is not complete. So, we know that it's not the final word on space and time and how all that works. So, we but the measurement is that if we look back in time, which we can do by looking from ancient light that's been traveling across the universe for for time, we see light from a time 13.8 billion years ago when the universe was very hot and very dense and just filled with hydrogen and helium gas, right? Basically, no stars, no planets, no galaxies. So, we know the universe was very different and it's the sort of universe you would imagine, you would predict if it had an origin at a big bang. But, the I'm so hedging it a bit because >> day without yesterday. >> Well, so we don't actually know what time is. So, because we don't know what time is,