Your Daily Equation #2: Time Dilation

Episode 02 #YourDailyEquation: Brian Greene talks time travel. Not the kind of time travel you encounter in sci-fi, but real time travel - the kind that's written into the laws of physics and understood using the time dilation equation. Watch to learn more about how and why our perceptions of space and time are not fixed, but relative.
If you have a favorite equation that you'd like Brian to discuss next time, be sure to let us know in the comments.
Even if your math is a bit rusty, join Brian Greene for brief and breezy discussions of pivotal equations and exciting stories of nature and numbers that will allow you to see the universe in a new way.
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[@CletusBoyce]

When I saw Pythagorean’s Theorem appear showing the relationship between time and space I had a religious experience. I am now one with the universe. 😌

[@andreranulfo-dev8607]

I had this 'almost religious' moment in the first time I learned that a mathematical instrument invented thousands of years ago, was used to discover something so complex.

[@dontfollow4704]

Cheers dig deeper

[@hareecionelson5875]

Irata, if you see this comment, (1/gamma)^2 + (v/c)^2 = 1^2 not only is this a^2 + b^2 = c^2 (pythagoras) this is x^2 + y^2 = 1, the unit circle. The big man. The circle of circles. also, the '1' has no units. Pure 1 goodness, chilling with time dilation and the speed of light.

[@hosh1313]

What you saw there was someone assume a theory to prove a theory. It was assumed that light can travel no faster or slower than c. It was also assumed that time is not universal so we get time dilation in addition to length contraction. TD is a false concept! It is mathematically unworkable.

[@hitulkothwala571]

Best explanation of time dilation ever!

[@protobudega]

I'm a Mathematician and would love to see your take on some classical equations (Euler identity, Riemann zeta function and such). But if you intend to go on this Physics/Relativity path I suggest two topics: 1) Talking about surfaces, curvatures and a conversation about the Gauss-Bonnet formula (Relation between topology and geometry, genus and curvature); 2) Talking about the inverse square law and the way it manifests in various laws of physics (Gravitation, Electric potential and others). This has been great, hope you do many more of those.

[@taufanaugusta8884]

Your picture profile checks out.

[@bunklypeppz]

I like the suggestion about the inverse square law. It's both powerful and strangely intuitive once you understand why it works.

[@vijay_r_g]

Sir ,I have a doubt

[@vijay_r_g]

Why is that ratio true. ∆ts/∆tm=L'/L

[@protobudega]

@@vijay_r_g He first used the famous equation for velocity V=ΔS/Δt Then he manipulated the equation to get Δt = ΔS/V And then he applied to our case. Note that in our case the velocity in both Δt and Δt' is C, the velocity of light, so when you make the ratio they end up cancelling each other. I hope it was understandable. :)

[@ulfafawzia]

This explanation is just as clear as the summer sky ❤️

[@thesavantart8480]

@@trnod Where do you live in the Netherlands? Lmao

[@marcuspratt5550]

@@trnod k

[@marcuspratt5550]

@@trnod kk

[@marcuspratt5550]

Ki

[@marcuspratt5550]

@@trnod j

[@chrisdiner7170]

Absolutely love these videos. Could listen to this all day. Brian Greene takes complicated ideas and makes them really easy to understand.

[@Photonphantom]

Yeah , for a dummy like me, this is very easy to understand

[@adams6782]

These videos are wonderful. Thank you so much

[@PaolaBarrientos]

So exciting! 🤗🤗🤗

[@bluefinance153]

Thank you Brian Greene

[@HystrixLignum]

A wonderful clear and comprehensive explanation. Thank You.

[@timjones1815]

Wonderful, thank you for taking up your time to so eloquently explain the beauty of maths and physics

[@alexalves76]

Love it! Great episodes!

[@KellyKOScraps]

Wow this is amazing. Thanks for explaining everything so clearly!!!

[@sreenathjohnsonsaysnotolgbtq]

Brian is the only onle who helps me understand easy and quick.

[@Photonphantom]

Me too 😊

[@yuryrabinovich8272]

Thank you Dr. Greene.

[@emj6724]

Dr Greene you are my Guru thank you for your work🎉

[@younessofri6789]

Loved you explanation Prof Greene! The use of the Pythagorean theorem was just beautiful. Thanks a lot!

[@hareecionelson5875]

there's another hidden pythagoras in the gamma equation; I recommend taking the inverse of gamma, 1/gamma= SqRt(1 - (v/c)^2). Square both sides and add (v/c)^2 to both sides. Another pythagoras.

[@albertcheng5378]

Thank you very much for your explanation. That's really clear and helpful.

[@Eduardo-tq5sk]

Thank you professor Greene!

[@MegaPrincess513]

Thank you so much for your videos!!!!

[@grainneconroy2193]

These videos are my recreation in every sense. Thanks so much.

[@jiaxu7395]

As somebody who doesn't know physics, I'm confused at if tm < ts, doesn't it also mean moving L is smaller than stationary L (since L=tc)? which means the moving world is smaller??

[@Photonphantom]

I know but thanks 😊

[@lindajean5029]

Something just clicked! Thank you for the great content.

[@wajidchadoora8818]

Thanks for having such an amazing demonstration

[@marvinrelleta9049]

Thank you Professor Brian Greene. You heard me. Thank you very much again. You're my Idol. I hope I can explain things like you did

[@johnrussel4483]

Thank you prof Green, what a great idea!

[@hasanhammadi1357]

Amazing!! All equations are more beutiful when explained by you professor

[@JeromyCarroll2010]

This series is really interesting. Thank you!

[@anthonyrussell8624]

Awesome, just awesome

[@bidyutbikashhazarika481]

Your explanation of the phenomenon is so simple and beautiful! Thanks

[@Photonphantom]

Yeah, but he would never reply to this

[@peterpackiam]

Thanks for sharing your time & knowledge, Brian

[@Photonphantom]

Yeah, he is a busy man. He does calculations all day

[@wajidchadoora8818]

Amazing to have such a demonstration...

[@DobrinWorld]

Thank you Brian!

[@Mr-ep2qi]

great explanation. thank you

[@Mark-rr7wq]

Love his explanations.

[@carolinaribeiro6868]

The simplest and most unique explanation of time dilation I've ever seen... Thank you so much for creating for us this daily reminder of why physics is so beautiful and astonishing.

[@rayhaney7143]

I thought I was fairly well versed in physics but I really don't see what speed has to do with time. In the example of two light clocks. These are closed systems the speed of the light doesn't change and the distance between the mirrors don't change. From the clocks point of view nothing changes. One on Earth traveling at some set speed and the one on a ship traveling close to the speed of light. How does the clock care what's going on outside of it? It's a closed system and nothing in the system changes.!???

[@anteconfig5391]

@@rayhaney7143 your perceived time doesn't change while you're moving but you and that clock are made of matter and energy which is effected by spacetime. Motion is defined as the difference in the change of position that occured within some time interval. Classically speaking, you cannot move without changing position and you cannot change position without going through time. The clock measures ticks and tocks while the speed of light cannot physically change. However, the velocity of the clock itself can change and if the ball of light stays in the clock as it moves then you can see that the ball of light would have a longer distance to travel from tick to tock. Since the speed of light remains constant there will be fewer ticks the faster the clock travels.

[@larche]

@@rayhaney7143 From each clock's point of view nothing is different since they are in non-accelerating frame of references. However, one observer looking at the other observer's clock will notice time dilation. The concept applies only to different frames of reference moving relative to each other. I see my clock ticking right, you see your clock ticking right, but from my point of view your clock is ticking slower, because it is moving and light has to travel a longer way to reach the upper or the lower wall of your clock (the walls of your light clock are moving very fast away from the light wavefront).

[@rayhaney7143]

@@larche Very interesting so of the clock was at Right angles to the motion would the light in this closed system miss the mirror entirely?

[@rayhaney7143]

I mean if the speed of travel is effecting the clock at all

[@tateviksimonian2344]

The beauty of physics never ceases to amaze me

[@Photonphantom]

Me too

[@chamindawijayasundara867]

excellent explanation to a complex concept.!

[@pedroleao8712]

I recommend the Heisenberg Uncertainty equation... Nice video!

[@stockita]

Thank you Professor.

[@ranathane]

Thank you Professor Greene for your explanation of a very difficult topic. I commented to ask what website has the clock differential demonstration. It's a powerful way to demonstrate the effect.

[@vikranttyagiRN]

Thank You Professor. These videos are absolute gem

[@Photonphantom]

For me, this is applicable 😊

[@bkkfootball]

I love this series

[@alaspooryorick9946]

Wonderful! Thanks so much mate. I'd absolutely love to look at some curved space-time stuff, though I understand completely that it's quite full on. Maybe the Friedman equations? Oh and the classical wave equation compared to the Schroedinger equation!!! Or just anything that you think is interesting, because you do a phenomenal job making everything engaging and exciting. Love your work Brian! Cheers

[@jeremykrystyan4906]

thank Dr. Green

[@paulc96]

Dear Prof. Greene, thank you for an excellent explanation of the Gamma factor. I have recently started reading your new book - "Until the End of Time" - and I am thoroughly enjoying it. May I also express my gratitude for the "Quantum Leap" episode, in the Fabric of the Cosmos TV series. That is probably the best ever visualisation & explanation of the Schrodinger Wave function, that anyone can ever see.. Thanks again and please keep up the great work. Best wishes from Paul C., on lockdown in West Wales !!

[@Photonphantom]

Do you think he would read this???

[@WTG15WTG17]

Amazing!

[@khuzaimakhan1894]

Great and easy to understand

[@undecidable42]

Very well done. Adding another vote for the Dirac equation!

[@rohanchdas3250]

Hello Sir, thank you so much for making our time worth by such beautiful explanation. I am a Physics student from India. I would urge you to kindly make a video on the Einstein's Field Equations and GTR as a whole. Thank you so much.

[@musicoscope]

Excellent and thank for dealing later with the twin paradox

[@quertyv12]

Wonderful explanation.

[@christopherinman6833]

Thank you again, sir. I remember an airplane experiment confirming this. I just looked it up and find it is the Hafale-Keating experiment (on Wikipedia), 1971. like the laser measurement of distance to the moon, it's nice to have experimental evidence demonstrate the irrefutably logical.

[@indysbike3014]

Maybe you can do the calculation how gravity affects time.

[@mikethek5494]

Its the same equation...

[@williamgothora4522]

@@mikethek5494 No. you're stepping into general relativity vs special relativity. A lot more complex

[@klammer75]

It is the same equation in principle(pun intended)...think Einstein’s equivalence principle...gravity and acceleration are indistinguishable or ‘equivalent’...let’s not try to over complicate some seriously complicated shit🤪🤯🤔

[@user-iz9ze7zf3v]

I understood it perfectly. Thank u😊

[@krisbollu]

Loved it!

[@amirhosseinmohammadizad236]

So many thanks dear professor for your nice explanation

[@kamilnadaf4369]

thanks proffessor Greene you really made those theories interesting and simple to understand, it would be really amazing to watch your explaination on one of the best equations you have discovered during hunt for superstring theory.

[@davidsansom1612]

Yes the elegance of the mathematical structure!

[@jagan541]

Thank you brian

[@user-qd2iw1js6f]

I think the time dilation derivation can be simplified: The stationary observer measures time for horizontal distance of the moving light clock as vΔt, but he also measures the same time for diagonal distance L’ as c Δt. As for the vertical distance L, it is measured by the moving observer as c Δt-moving. (I.e., the time he measures on the moving inertial frame for the up and down trajectory of the light). Applying the Pythagorean theorem the dilation relation follows between Δt and Δt-moving. So no need to assume L’/L = stationary time/moving time proportion before hand. Am I wrong professor? Thank you for all you do for the general public.

[@lalalafamille]

Brilliant presentation... I finally understood how time and space are related... It seems now so simple... Before it was like if I could not understand that the earth could not be anything than flat... Thank you.

[@manishsahu8860]

Thanks Sir, You are owesome

[@hussammustafa5267]

I'm a 4th year undergrad in physics and I have never fully understood time dilation until this explanation. I've watched other videos on it and now I truly understand. Thank you

[@hareecionelson5875]

as a 4th year student, have you thought that it was suspicious that a v/c of 0.5 gives a gamma of 2/root3, and a v/c of root3/2 gives as gamma of 2? smells like... sine and cosine of 30 and 60 degrees, no?

[@gonzalofontana]

Brian i would love to see the explanation of the extended version of E=mc2 with momentum and its implications. Thank you for the vídeos!

[@rahil613]

Sir, I great fan of yours, the way you explain the complicated things in simpler form is awesome. I have request if you can present something on Nibru.

[@sergiomachado6136]

Thank you Brian it is wonderful how you make us feel belonging to the universe

[@ManWhoUsesComputer]

These are awesome

[@broken_radar]

Thank you for doing this Brian. I have watched many of your presentations but I like the added math here. It helps greatly to understand the ideas.

[@lindakilmer2548]

I can’t wait for Brian’s next book!!

[@ayyappaas]

Hi Prof Greene. Amazing video. I would like you to touch on the laws of thermodynamics in a video and go a little bit in to the concept of Entropy and how that ties back to how we deal with the concept of time. Thank you

[@rickmorrisrigar]

Awesome, great idea to have this on every day, Excellent explanation Dr. Greene, How about how Gravity effects Time would be interesting !!

[@trevorjames2051]

Agreed, also how it affects the speed of massless particles.

[@sbhagwat2000]

Thanks for doing this. Me and my 2 daughters(11 and 8) are really enjoying these sessions. Some point please talk about the second law of thermodynamics.

[@knarfx4732]

Awesome 🙌

[@dandelion6692]

so excited to watch you live! 🍏

[@dandelion6692]

thanks for sharing :)

[@dandelion6692]

i'm interested in quantum entanglement, particles, anything quantum :)

[@shahriarkarimi1939]

I love the way you explain; 👌👌

[@jengagame6137]

One of my favorite equations is the one for exponential growth and decay. I always was thought that it was awesome that one equation could be used to calculate compound interest and the growth rate of bacteria. I think it's also pertinent equation for our current situation.

[@mapeandrews3951]

Jenga Game would love to see that one as well.

[@justdata3650]

This daily equation is just an awesome idea. Thanks Brian. If you run out of equations I might suggest you do different types of series. For example, a mini-series on famous (or not so well known might be even more interesting) thought experiments which of course is closely tied to equations would be nice. I personally wondered if it would be valid to think of space as being "eaten up" by large gravitational bodies instead of space only being stretched which is how it's always described which you thankfully touched on in your first episode (if I remember correctly) as I always had a problem visualizing a blackhole infinitely stretching space but if it's getting to "gobbled up" spacetime that infinity issue goes away. And now learning about dark energy it's like there's a counterpart where dark energy could be creating spacetime and blackholes destroying it making a nice balance of mechanisms for our universe... but I have never had a physicists or cosmologist friend to run this notion by so I've never had an feedback on whether such a way of looking these has any validity.

[@Photonphantom]

Do you think he would ever read this " paragraph "

[@lsuarez2007]

Great video!

[@behnamansari4704]

Thank You

[@wajidchadoora8818]

Outstanding

[@BigEarlPearl1]

these equation videos are awesome. thank you for sharing this knowledge, Brian!!

[@michaelmcclure94]

This is awesome

[@MegaPrincess513]

The best professor ever

[@Shenron557]

I would like to see a video on the Twin Paradox. One of the explanations I found says that the difference in age comes due the acceleration (General Relativity) that the twin on the rocket ship experiences when he turns around to come back to earth. This acceleration is not experienced by the twin on the earth. I'm not sure if this is the wright answer, or if an explanation for the paradox can be given completely within the realms of Special Relativity.

[@jeremypnet]

It’s three years later and this is the only comment I can see addressing the twins paradox. Your explanation is completely correct, I think. The twin on the spaceship has to turn around and come home which involves acceleration and special relativity can’t deal with acceleration.

[@robertokeefe9952]

Great presentation....what writing/drawing program do you use on your iPad? It’s nice and simple (for those of us teaching at a distance).

[@localtitans4166]

Thanks sir u r helping a lot in this quarantine

[@abhaypillai970]

Awesome professor. That's the true elegance of physics. Unfortunately many physics lecturers miss this wonderful opportunity, as being seen in India. They just don't care about it's elegance, just memorizing everything. The Indian have ended up thinking Engineering is the best and nothing could exceed this, but it is just because they doesn't know about theoretical physics.

[@euflo3163]

Prof Brian, many thanks for such a beautiful presentation. I have a simple question: in this demo the clock is defined as a cyclical motion device, but if is not defined like this, how can be defined otherwise? And please, please make a course of a General Relativity Theory on World Sience U site.

[@amaankhan3092]

Brian Greene..... Greatest name in Physics...

[@ellehill6719]

Thanks again Brian amazing lecture! Do you think you could talk about the equation for the Schwarzschild radius? I would love to learn more about black holes!

[@DavieboyLondon56]

Really great series. Thanks!

[@joannagase6392]

Thank you Brian. I am learning so much. Joan from Manchester, England.

[@Photonphantom]

Don't give info about your self

[@gedlangosz1127]

Excellent video Professor Greene! I look forward to the next instalment. I'd like to see the derivation of the E= mc² equation. I also want to see the equations of General Relativity, Maxwell's Eqns. Schrödinger's eqns, Dirac's equations. That's sufficient for a few weeks.......

[@adventuresinphysics5069]

Hi Brian! Kevin here. At 18:24, you said if we grew up in a world that had our daily activities at relativistic speeds, we would have better appreciated the effect speed has on time. However, I think that may not be totally true because we'd equally be used to that particular scale of time if we existed in a relativistic world. It may even be more difficult for us to appreciate Time dilation in such a scenario since we may have to be moving at slower speeds to observe how time moves faster for such cases; just because we may not be able to get any faster since we can't get faster than light. Just my thoughts, Prof. I hope you understand my suggestion

[@elmehdi8358]

Thank you sir

[@wajidchadoora8818]

I was having some confusion regarding time dilation but now after going through last demonstration everything is clear in my mind........

[@schrodingersdad6077]

I love you Mr Greene

[@SafeTrucking]

Once again, Brian, with the current pandemic, how about an analysis of the general logistic equation? Particularly the differential form, but also the integral. It would be a very useful contribution to public understanding if done well, I think. Love the concept behind this series, thanks.

[@well583]

I know this is three-years-old already but I just bumped into it and I loved it, my question is - of course - about time travel in this specific equation, so what you've established is the theoretically you can time travel in the future if you travel at or near the speed of light, what I also understand is it has been established that the universal speed limit IS indeed the speed of light, the question is that if by any way it is possible to exceed the speed of light, would time theoretically go backwards? Or maybe the speed of light is sort of the highway on which time travels so it doesn't matter YOUR speed just how fast you get from point a to point b on that highway?

[@sanwer2996]

Good effort sir....👏👏👏👏👏

[@mauricioweber8879]

Wonderful