Brian Cox breaks down the most mysterious scale in the cosmos
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“It’s a very, very beautiful calculation, but it’s the best example I know of the relationship between these rather abstract quantities perhaps and something that you can look at in a telescope.”
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What happens when you try to look too closely at the fabric of the universe? When we gaze at a Planck length, a scale so small that even light becomes useless for observation, physics pushes back.
The Planck length is not just a tiny number, it’s a boundary where gravity, quantum mechanics, and relativity collide. Physicist Brian Cox explains why the measurement is a portal to the deep structure of reality, and why going beyond it may break the boundaries of our understanding.
0:00 Introduction
0:45 The importance of measurements
2:40 What are the fundamental quantities?
7:20 How important is the Planck length?
9:20 Why you can’t approach the Planck length
10:30 A theory with more dimensions
13:00 What keeps a star from collapsing?
14:42 The uncertainty principle
17:36 The Planck mass
Read the video transcript ► https://bigthink.com/series/the-big-think-interview/planck-scale/?utm_source=youtube&utm_medium=video&utm_campaign=youtube_description
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About Brian Cox:
Brian Cox obtained a first class honors degree in physics from the University of Manchester in 1995 and in 1998 a Ph.D. in High Energy Particle Physics at the DESY laboratory in Hamburg. He is now Professor of Particle Physics at the University of Manchester, The Royal Society Professor for Public Engagement in Science and a Fellow of the Royal Society.
Brian is widely recognized as the foremost communicator for all things scientific, having presented a number of highly acclaimed science programs for the BBC watched by billions internationally including ‘Adventures in Space and Time’ (2021), ‘Universe’ (2021), ‘The Planets’ (2018), ‘Forces of Nature’ (2016), ‘Human Universe’ (2014), ‘Wonders of Life’ (2012), ‘Wonders of the Universe’ (2011) and ‘Wonders of the Solar System’ (2010).
As an author, Brian has also sold over a million books worldwide including ‘Black Holes’, ‘Universal: A Guide to the Cosmos’, ‘Quantum Universe’ and ‘Why Does E=mc2?’ with co-author Professor Jeffrey Forshaw. He has set several world records for his sell-out live tours, including his most recent tour Horizons which has taken in venues across the globe.
@JDHobbs
June 9, 2026 at 7:06 pm
Planck didn't believe in QM, th;ough he calculated both "h" and "k" (the Boltzmann constant) before anyone else, even Boltzmann.
@mnukr8960
June 9, 2026 at 7:06 pm
Awesome
@grzegorzt.6511
June 9, 2026 at 7:06 pm
Z góry dziękuję
@JoshShannon-em2ft
June 9, 2026 at 7:06 pm
if I'm understanding properly, then the distance discussed here is only a social construct in our minds. our hearts see no distance, remember that♥
EDIT: forget it, wrong discussion. i was watching a philbro vid right before this and got my wires crossed. . .
@micheldenert
June 9, 2026 at 7:06 pm
Since the eighties I am trying to explain that time does not exist, which means that distance doesn't exist. For all I care, the Higgs-Boson particle could contain multiple universa. We can travel to another galaxy in a blink of an eye. Due to our fysical restrictions and narrow minded insights as humans, we will probably, unfortunately, never understand. @micheldenert
@dolex161
June 9, 2026 at 7:06 pm
“I don’t cary these numbers around, I can look it up” tell that to my uni teacher
@PJW.418
June 9, 2026 at 7:06 pm
So isn't defining cosmic constants using human constructs like meters and seconds fundamentally wrong?
@StephanLuik1
June 9, 2026 at 7:06 pm
The meter was based on the quarter of the circumference of the Earth, by the French. Only freedom units are based on human body parts.
@blovehana
June 9, 2026 at 7:06 pm
When I explain basic math I ignore the video and move on. Humanity is largely saf
@bravedavy123
June 9, 2026 at 7:06 pm
Get a haircut and get a real job.
@Socke-4you
June 9, 2026 at 7:06 pm
I have a question—purely a thought experiment: If the Planck length were a reverberation—that is, a collision of frequencies from a higher dimension—wouldn't all matter condensing within this reverberation have to align itself with that specific frequency? And wouldn't this reverberation effectively constitute the "speed limit" that light, fundamentally speaking, demonstrates to us?
@robinholland1136
June 9, 2026 at 7:06 pm
I'm not a mathematician, even less a physicist and even have problems with basic arithmetic at times. I do, however, find this fascinating. I understood the words, but shall have to watch again to try to understand the detail a little better. I have a question, which might seem silly to the initiated, and it is this. If the Planck length describes the smallest possible length in the universe, is there an equivalent at the other end of the scale? Is there a maximum length which cannot be breached? I imagine that there isn't, but why would that be so? Again, forgive my ignorance, but the question is an honest one.
@DarSaqib-jh1re
June 9, 2026 at 7:06 pm
Brian cox explanation 🧠❤️🩹
@SeaDawg77
June 9, 2026 at 7:06 pm
The Planck length is so tiny that it defies imagination. I sometimes turn to that video on the scale of the universe for perspective. But even the video doesn't do that tiny scale justice.
@Smallscaleworld
June 9, 2026 at 7:06 pm
As a complete amateur, I felt it needed another five minutes, he started to talk about white dwarves, then said first we need to understand suns, gave a quick explanation, then went back to Planck. Am I to understand that what he was saying is a white dwarf has to be less than or barely equal to 1.4 sun masses, and anything else/anything over 1.41 sun masses, will lose cohesiveness and become a red giant?
@grzegorzt.6511
June 9, 2026 at 7:06 pm
Wieze ze to obejrze po polsku
@grzegorzt.6511
June 9, 2026 at 7:06 pm
Dasz rade.czy nie
@Inverted-Compass
June 9, 2026 at 7:06 pm
Mass less must therefore equal the pressure of a quantum fluid state needed to travel at the speed of light. ❤
Length therefore must be the horizontal size of a Quantum Fluid State. ❤
Therefore the quatum fluid density of a electron decreases as the pressure increases, trying to push the quantum fluid state to the same fluid pressure as the speed of light. ❤
Isolated Planck's Constant…
The maximum kinetic energy of a photoelectron (or Isolated Planck's Constant) is given by 𝐸(max) = ℎ 𝑓 − 𝑊, where ℎ is the Planck constant, 𝑓 is the frequency of the incident photon, and 𝑊 is the work function (the minimum amount of energy required for an electron to be emitted from a surface). Planck's constant is a dimensioned quantity and so its magnitude can literally be any positive value, it is a measure of how closely two vectors align, in terms of the motion of individual atoms and molecules, a predetermined thermal vibration. it is the thermal energy contained in the motion and vibration of its molecules. The relationship between momentum and wavelength for thermal vibration is given by p(linear momentum) = h(Plank's Constant)/λ(wavelength), and the relationship between energy and frequency of thermal vibration is E(Energy) = h(Plank's Constant) f(Frequency), These are the same thermal vibration relations we have for the photon.
If it's Absolute it's Thermodynamics…
@zakriver4819
June 9, 2026 at 7:06 pm
My god, it takes him forever to get to the point.
@JakobSanvig
June 9, 2026 at 7:06 pm
The meter is not based on biology. Not his finest hour
@humblegrenade118
June 9, 2026 at 7:06 pm
What is infinity, does it have a start and no end, does it go small as well as large
@João-e1u5j
June 9, 2026 at 7:06 pm
I could totally picture Brian Cox explaining the plank length with his usual hand gestures
@daandecloe8754
June 9, 2026 at 7:06 pm
The meter was originally defined as one ten-millionth of the distance from the equator to the North Pole, measured along a meridian through Paris.
It has nothing to do with the relation of your arm or another body part.
@ahole5407
June 9, 2026 at 7:06 pm
🤨ok…… Well then someone should pay me millions because I know EVERYTHING he says they dont know…
@barneyrubble9309
June 9, 2026 at 7:06 pm
So Brian doesn't know what a metre is …seriously 😅
@aRecRandom
June 9, 2026 at 7:06 pm
I tried to measure the length of my Planck ….this is why I’m still singularity
@KohrMoncier
June 9, 2026 at 7:06 pm
“Pure talent 👌”
@KohrMoncier
June 9, 2026 at 7:06 pm
“So good 🔥”
@sketch-y-7
June 9, 2026 at 7:06 pm
The more we study the universe, the more questions we find the need to answer.
@SurprisedDivingBoard-vu9rz
June 9, 2026 at 7:06 pm
May be it is a clustering length. Or squzee factor. The light from the sun gets focused by clouds to get thunder. During night it is stored energy of focal points. Addition division multiplication and subtraction. Is the sequence of matter. Depends on power factors. But why because the universe is accelerated. But there is no proofs. Why there are prime numbers nobody knows but they know the definitions of prime.
@maxthemagition
June 9, 2026 at 7:06 pm
There be the quantum world apparently.
Hard to visualise for sure.
Perhaps every cell in your body lives in the quantum world.
Nobody can understand the quantum world…
The fact that the Zygote contains all the information and program to split and grow into anthing from a tree to a Dinosaur…That Zygote has the software and machinery to build you….
It is as though the Zygote has come from the Quantum world into our World as we see it and experience it.
We now see there is two realities….The Quantum World and our World as we experience it.
But every cell in our bodies may have originated from the Quantum World.
That Zygote is the miracle of life.
How many living cells are there today?….Ask an A.I….The answer is quite astonishing….They exist is animals, plants and bacteria etc
@USAPatriot-001
June 9, 2026 at 7:06 pm
Thank you.
@Totozme
June 9, 2026 at 7:06 pm
Only Wemby has a 1 meter forearm
@NickyNustar
June 9, 2026 at 7:06 pm
The unit of measurement as I see aliens / angels seeking to teach me from experience IS light knowledge
Comments are closed.