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Time Dilation
1hr 19mins
Theoretical physicist Jim Al-Khalili explores why our sense of time may be incredibly misleading, including the idea that past, present, and future might all exist at once.
The Universe is expanding, the expansion is accelerating, and some galaxies even recede faster-than-light. Can we see a change in real time?
The VENUS survey isn't about planets at all, but about finding multiply-lensed supernovae. The ambition? To save the expanding Universe.
Every observation out into deep space is also a look back in time.
We see objects whose light only arrives just now. But we see them as they were in the past: when that now-arriving light was first emitted.
The problem for galactic-scale civilizations comes down to two numbers.
Gravitational waves are the last signatures that are emitted by merging black holes. What happens when these two phenomena meet in space?
Physicists recently created Coordinated Lunar Time, a time zone for our Moon.
Time is relative, not absolute, as gravity and motion both cause time to dilate. Your head and feet, therefore, don't age at the same rate.
The passage of time is something we all experience, as it takes us from one moment to the next. But could it all just be an illusion?
Our thermodynamic arrow of time explains why the entropy of any isolated system always increases. But it can't explain what we perceive.
Traveling back in time is a staple of science fiction movies. But according to Einstein, it's a physical possibility that's truly allowed.
From unexplained tracks in a balloon-borne experiment to cosmic rays on Earth, the unstable muon was particle physics' biggest surprise.
2023's Nobel Prize was awarded for studying physics on tiny, attosecond-level timescales. Too bad that particle physics happens even faster.
9mins
Ever wonder what would happen if we got sucked into a black hole? Turns out we could live in it for a while — if it was big enough.
Headlines have blared that quasar ticking confirms that time passed more slowly in the early Universe. That's not how any of this works.
Einstein's relativity overthrew the notion of absolute space and time, replacing them with a spacetime fabric. But is spacetime truly real?
Time gets a little strange as you approach the speed of light.
Everything everywhere all at once.
In the grand scheme of the cosmic story, a single year isn't all that significant. But over time, the annual changes really add up!
Over the past 50 years, 27 leap seconds have been added to our time.
The concept is so complex that scientists still argue whether it exists or if it is an illusion.
John Templeton Foundation
If you can model anything in the Universe with an equation, mathematics is how you get the solution(s). Physics must go a step further.
Ever since the start of the hot Big Bang, time ticks forward as the Universe expands. But could time ever run backward, instead?
We live in a four-dimensional Universe, where matter and energy curve the fabric of spacetime. But time sure is different from space!
Atomic clocks keep time accurately to within 1 second every 33 billion years. Nuclear clocks could blow them all away.
Time isn't the same for everyone, even on Earth. Flying around the world gave Einstein the ultimate test. No one is immune from relativity.
Equations that describe time travel are fully compatible and consistent with relativity — but physics is not mathematics.
Extremely precise atomic clocks are not just of theoretical interest; they could help detect impending volcanic eruptions or melting glaciers.
We take for granted that time is real. But what if it's only an illusion, and a relative illusion at that? Does time even exist?