Articles, Blog

Lorentz Transformations | Special Relativity Ch. 3

January 14, 2020


The goal of relativity is to explain and understand
how motion looks from different perspectives, and in particular, from different moving perspectives. It’s easy enough to describe motion itself
– if something is moving relative to me, that means it has different positions at different
times, which I can plot on a spacetime diagram. This straight line corresponds to motion at
a constant velocity of say, v units to the right every second. And the question we’re interested in is what
do things look like from the moving perspective? Of course, the answer to this question is
a physical one, and is determined by experimental evidence gathered by actually moving. And that evidence will come into play, but
first we need to understand what it means, in terms of spacetime diagrams, to view something
from a moving perspective. We’ll start with a key property of spacetime
diagrams: when someone draws a spacetime diagram from their own perspective, on that diagram
they’re always, for all time, located at position x=0, since they’re always a distance of 0
away from where they are. Or in other words: a spacetime diagram like
this represents your perspective only if your worldline is a straight vertical line that
passes through x=0. If, on a spacetime diagram, the worldline
describing your motion leaves x=0 and goes anywhere else, that means you’re moving relative
to the perspective of that particular diagram, and thus it’s not your perspective. With this in mind, to describe how things
look from the perspective of a moving object, like this cat, we simply need some way to
transform spacetime diagrams that makes the worldline of the cat into a straight vertical
line through x=0; or in other words, we want to make the spacetime diagram where the cat
is moving into one where the cat’s worldline coincides with the time axis. That’s not something we can do just by sliding
the whole plot left or right or up or down, like we’ve done for perspectives from different
locations. No, changes of velocity require some sort
of rotationy thing to change the angle of the worldline, and importantly, whatever this
rotationy thing does should be generalizable to a world line at pretty much any angle,
since there was nothing special about the particular speed the cat happened to be going. There are also two important pieces of experimental
evidence that we’ll need to take into account: first, if I measure the cat as moving at a
speed v away from me, then the cat will measure me as moving at that same speed v away from
it, and likewise if we’re moving towards each other. Which means we not only want to transform
the spacetime diagram in a way that the cat’s angled line becomes vertical, but we also
want the angle between our two lines to stay the same after the transformation – that
is, from the cat’s perspective, I should be moving. The second piece of evidence we’ll come to
later. Let’s focus just on the section of the cat’s
worldline from time t=0, where it’s at x=0, to t=4, where it’s at x=2. This section is a straight line between those
two points, and we want it to end up as a straight vertical line, so we can simply leave
the t=0,x=0 point unchanged while moving the t=4,x=2 point onto the time axis (where x=0). And there are really only three general possibilities
for how to do this: either this point gets moved onto the time axis while keeping it
at the same point in time, t=4, or it gets moved onto the time axis at an earlier time
(say, t=3), or a later time (like t=5). There’s a very nice geometric way to picture
these possibilities. If we think again of motion on a spacetime
diagram as a series of snapshots, like, at time t=0 the cat is at position 0, at time
t=1 the cat is at position 0.5, at time t=2 the cat is at position 1, etc, then the transformation
where points move to the time axis and keep the same time just looks like sliding each
snapshot over a corresponding amount; the possibility where points move to the time
axis at a later time looks kind of like some sort of rotation around the origin; and the
possibility where points move to the time axis at an earlier time looks kind of like
some sort of squeezy rotation. The reason these last two involve rotating
the snapshots rather than just sliding is to make sure that the angle between the cat’s
worldline and my worldline stays the same before and after the transformation – it’s
a fun little geometry puzzle to understand why. Now, among these three, the option that makes
the most intuitive sense based on our everyday experiences of the passage of time, is that
a given point in time should stay at the same point in time, and just slide over to the
time axis. I mean, we don’t noticeably experience time
travel every time we hop on a train or bike or plane. And this sliding does mathematically work
– if we move things at time t=1 a half meter to the left, and things at time t=2 one meter
to the left, and so on, then we’ll have a description from the cat’s perspective – the
cat’s not moving, and I’m moving to the left half a meter every second. It works for other speeds, too. If we want the perspective of somebody who’s
going a meter per second to the right relative to the cat, we can slide the snapshots over
even farther, and now the cat’s going a meter per second to the left, and I’m going a meter
and a half per second to the left. And of course we can slide back to my perspective
from which the newcomer is going a meter and a half per second to the right. This kind of sliding change of perspective
is normally called a “shear transformation,” but that’s when both dimensions are space
dimensions: since one of our dimensions is time, a shear transformation represents a
change in the velocities of things, so in physics it’s called a “boost.” As in, rocket boosters boosting you to a higher
speed. However, it turns out that boosts in the physical
universe are not actually described by shear transformations. This is where the second and most famous piece
of experimental evidence comes in: the speed of light. As you’ve probably heard, starting in the
late 1800s, physicists built up mountains of experimental and theoretical evidence that
the speed of light in a vacuum is always the same, even if you measure it from a moving
perspective. This is, of course, entirely unintuitive from
our everyday experiences with velocities, where if you throw a ball from a standstill
and then from a moving vehicle, the ball thrown from the vehicle will be moving faster relative
to the ground. And yet, experimental results show that light
does not behave like everyday objects: shine light from a standstill, or from a moving
vehicle, and its measured speed relative to the ground will be the same. Shear transformations simply can’t accomodate
this feature of light’s behavior: they change all velocities equally by sliding each snapshot
an amount proportional to its time. No velocity remains unchanged – if you draw
the worldline of a light ray and then change to a moving perspective using a shear transformation,
the speed of that light ray will change, which is wrong. Luckily, one of the other two options for
boosting to a moving perspective can accomodate a constant speed of light: remember the transformation
where the snapshots do a kind of squeeze rotation, and points move to the time axis at earlier
times? This kind of transformation can amazingly
leave one speed unchanged, even while it changes all other speeds. More amazingly, the unchanged speed is left
unchanged in all directions. Let’s do an example. Here’s a set of snapshots from my perspective
with a slow-moving sheep and two fast-moving cats, and let’s suppose that we have experimental
evidence that cats always move at the same speed regardless of perspective. If we want to describe this situation from
the perspective of the sheep, we can’t simply slide the snapshots over so the sheep isn’t
moving and its worldline coincides with the time axis, since that would change the speed
of the cats. But, if we slide and rotate and stretch the
snapshots like this, then look – we’ve transformed the diagram to both describe things from the
sheep’s perspective and keep the cats moving at the same speed they were before. You might note that the various cats appear
to be spaced out differently along their worldlines, but that just means that the constant-time
snapshots from my perspective aren’t constant-time snapshots from the sheep’s perspective. The important thing is that the angle of the
cats’ worldlines – which represents their speed – has remained unchanged. It’s kind of amazing to me that this works
at all; that it’s mathematically and physically possible for all speeds except one to change! But it is possible with these squeeze rotationy
things, and they’re the answer to our question of how to describe motion from a moving perspective. Well, not by keeping the speed of cats constant,
but by keeping the speed of light constant: by doing squeeze rotations so that a moving
perspective’s angled worldline becomes vertical without changing the speed of light – that
is, without changing the slope of the worldlines for light rays. These squeeze rotationy things are called
Lorentz Transformations, named after one of the first people to derive the correct mathematical
expression for them – it looks kind of like the equation for rotations that we saw in
the last video, and I’ll post a followup video showing how to derive this using just a few
simple assumptions and experimental facts. Lorentz Transformations are at the heart of
special relativity – they’re the thing that Lorentz and Einstein and Minkowski and others
figured out was the correct description of how motion looks from moving perspectives
in our universe, and they’ll be the foundation of the rest of this series, too. Now, as we’ve seen, Lorentz transformations
look different depending on what speed you’re trying to keep constant, or how you’ve scaled
your axes. Normally, physicists draw their spacetime
diagram tickmarks such that if every vertical tickmark represents one second, a horizontal
tickmark represents 299,792,458 meters, which means that the speed of light, which is 299,792,458
meters per second, is drawn as a 45° line – to the right for right-moving light, and
to the left for left-moving light. With this scaling, a Lorentz Transformation
that leaves the speed of light constant simply consists of squeezing everything along one
45° line and stretching along the other in a particular, proportional way. You can see immediately how this changes the
angles of all of the other worldlines, that is, changes how we perceive their speeds,
and yet doesn’t change any of the light rays. And it turns out that it’s possible to actually
build a mechanical device that does Lorentz Transformations for you: here it is! Just like how a globe has the structure of
rotations built into it in a fundamental way, and you can simply turn the globe to see how
rotations work, rather than doing a lot of complicated math, this spacetime globe has
Lorentz Transformations built in: it does the math of special relativity for you, allowing
you to focus on understanding the physics of motion from different perspectives! Here’s a quick example: from my perspective,
I’m always at the same position as time passes, while the cat is moving away from me to the
right at a third the speed of light, and the light rays from my lightbulb are moving out
to the right and left. Using the time globe, I can do a Lorentz transformation
to boost into the cat’s perspective. And from the cat’s perspective, the cat – naturally
– stays at the same position as time passes, while the cat views me as moving away from
it at a third the speed of light to the left, and the speeds of the light rays from my lightbulb
are still the same, still at 45° angles. I just love how tangible and hands-on this
is – normally when people are first introduced to special relativity and how motion looks
from different perspectives, it’s done with a bunch of messy, incomplete, algebraic equations
– but you don’t need the equations to understand the ideas of special relativity and how motion
looks from different perspectives. You just need an understanding of spacetime
diagrams, and a time globe. And so in the rest of this series, I’m going
to be using the time globe extensively to dive into all of the normally confusing things
you’ve heard about in Special relativity: time dilation, length contraction, the twins
paradox, relativity of simultaneity, why you can’t break the speed of light, and so on. I have to say a huge thank you to my friend
Mark Rober for helping actually make the time globe a reality (you may be familiar with
his youtube channel where he does incredible feats of engineering, like this dartboard
that moves so you always hit the bullseye). He devoted a huge amount of time, effort,
and engineering expertise to turn my crazy idea into this beautiful, precision, hands-on
representation of special relativity and I’m supremely indebted to him – this series
wouldn’t be possible otherwise. And if you’re eager for more details, I’m
planning another whole video about the time globe itself. In the meanwhile, to get more hands-on with
the math of special relativity, or economics, or machine learning, I highly recommend Brilliant.org,
this video’s sponsor. In conjunction with my video series, Brilliant
has rolled out their own course on special relativity with their own unique illustrative
scenarios – like relativistic laser tag to understand lorentz transformations. If you want to understand a mathematical topic
deeply, there’s really nothing better than thinking through the ideas and solving problems
yourself. And Brilliant helps you do just that. Once you’re ready to go in-depth into special
relativity (or perhaps linear algebra or group theory, which are both also relevant for relativity),
you can get 20% off by going to Brilliant.org/minutephysics. Again, that’s Brilliant.org/minutephysics
which gets you 20% off premium access to all of Brilliant’s courses and puzzles, and lets
Brilliant know you came from here.

You Might Also Like

100 Comments

  • Reply Paul Moody September 9, 2019 at 1:16 pm

    Bear with me, but the cats moving at C are rotated to the time axis and appear closer together. Is this what is known as a Lorentz contraction?

  • Reply Supertyp September 9, 2019 at 1:18 pm

    I don't understand. When you squeeze the lines, the light speed changes too? The light rays on the one arrow get squezed together the other more stretched out so the one light ray moves slower the other faster.

  • Reply Paul Moody September 9, 2019 at 1:19 pm

    Is this what also causes light to red or blue shift as well?

  • Reply Andras Libal September 9, 2019 at 2:39 pm

    Love the drawings.

  • Reply 1.21Gw September 9, 2019 at 5:07 pm

    Very interesting…

  • Reply Sold to be Diers September 9, 2019 at 5:52 pm

    So the universal axis belongs to non other than… I AM THAT I AM. No?
    Speed of light will increase as it approaches the event horizon. No?
    Or; we could just agree, to agree,
    to what the name of what 2 agreeing Physicists would be called… a ''Paradox.'' -9919

  • Reply cwaddle September 9, 2019 at 8:43 pm

    Wow for the first time in my 33 year old life i think i am getting special relativity

  • Reply jdawghatesyou September 9, 2019 at 10:24 pm

    I went through much of grad school for my PhD in physics. I was always bad at relativity but it didn't matter because it wasn't part of my field. I ended my grad school with a masters and went into the private sector to work, and this is the first explanation of Lorentz transforms that has ever made sense to me. I need to go revisit my old books now.

  • Reply Joshua Spector September 9, 2019 at 10:26 pm

    Is there somewhere i can purchase one of those globes? I super-mega want one!

  • Reply thatchesterguy September 10, 2019 at 12:50 am

    I have a question relating to the experiment done with polarized light. When the angle of the second lens is adjusted there is a nonstandard coralation as to how many particles pass through. Can your space time globe be used to track the difference?

  • Reply Al Bundy September 10, 2019 at 2:53 am

    Thats a cat?

  • Reply Le Marquis September 10, 2019 at 6:41 pm

    that desn't proof y light can't vary in speed and don't let us know what happen to a photon trap…. Annoying when you realise Lorentz did a math trick to fit a theory and not to fit the truth…. And IT IS PONTCARRE not Einstein !

  • Reply Kameron Cole September 10, 2019 at 10:54 pm

    But how do you do it in real time frequentley while controlled.

  • Reply Gerard Gilgallon September 11, 2019 at 8:00 am

    Almost the default mistake with these videos. The tutor talks too fast.

  • Reply mark hughes September 11, 2019 at 8:28 am

    Slide rotate and stretch – Einstein in your pocket!

  • Reply Ham Repair September 12, 2019 at 2:14 am

    Make the cat communicate witb a spider, then you got something.

  • Reply David Quispe September 12, 2019 at 12:33 pm

    OMG this is amazing!!!

  • Reply A Cat is fine too September 12, 2019 at 12:40 pm

    It's true. Cats always move at the speed of light.

    when you chase them with a squirt gun…

  • Reply Parth Kumar September 12, 2019 at 7:07 pm

    Time globe!!!! Wow

  • Reply victor richenstein September 13, 2019 at 1:36 am

    Been trying to understand this for years. The time globe gave it a visual model that really helped. Thanks

  • Reply Victor de Oliveira Asfora September 13, 2019 at 3:50 am

    7:33
    subliminal (more on this later) xD

  • Reply Vishnu M Aiea September 13, 2019 at 12:05 pm

    Excellent! I think that "time globe" can be motorized for a more precise and smooth motion, and Mark can of course do it!

  • Reply Lawrence Reitan September 13, 2019 at 6:30 pm

    I like these educational videos, but why do they speak soooo fast?!

  • Reply erictko85 September 14, 2019 at 2:15 am

    Wow. You are a great teacher.

  • Reply smudden September 14, 2019 at 2:23 pm

    I hate that I can hear this small "munching" sound whenever he speaks. It's fcking annoying xD

  • Reply Socks With Sandals September 14, 2019 at 5:43 pm

    Oh, I see. 
    There are hyperbolic rails keeping the product of the eigenvalues constant.
    c².
    😵

  • Reply Optimus September 15, 2019 at 10:34 am

    shameless plug for ur sponsor. gross.

  • Reply Frank Lippert September 15, 2019 at 10:54 am

    So Henry is not just abusing cats like Schrödinger did, he's mistreating sheeps as well.

  • Reply Circle of fifth September 15, 2019 at 6:36 pm

    this is excellent

  • Reply blahhhhahah September 16, 2019 at 12:22 am

    Ex – Pear – iment
    not
    Ex – Peer – iment

  • Reply S. Paul Dev September 16, 2019 at 4:13 pm

    Great job explaining complexity by simplicity. Can nuclear physicists and cosmologists do the same?

  • Reply Ratan Deshpande September 17, 2019 at 1:14 am

    Thats great what I have visualised in plane graph paper you have established with a mechanical device

  • Reply fntime September 17, 2019 at 4:35 am

    I'm sure most of the people watching this video are smarter than me.
    But, why is the narrator talking so fast and drawing so fast?
    I'm presuming everyone else understands this and it's just my ignorance
    that is interfering with my understanding. I think I'll look elsewhere.

  • Reply Lloyd David Lieberman September 18, 2019 at 12:10 am

    I could not stand to watch past 2:39, this is far better Suited to a “physics student” than to your average YouTube viewer. I hope you can accept it as constructive criticism that this Reminds me of all the confusion over particle versus wave i.e. wavicle; and except for very few or perhaps those using amphetamines confuses the issue needlessly. There is an animation it is made intuitively clear by means of a dimensionally aware (unfortunately I cannot reference it at the moment for you) but within a 10 to 20 CGI A substantial Demonstration of quantum insight is created rather than these linear contortions

  • Reply n2cat September 18, 2019 at 1:24 am

    Why bother with practical and experimental physics. Theories are easier. In a couple of decades there will be thousands of theories but not a single one would be practical. Rid yourselves of drugs people. Do something useful and practical.

  • Reply Biao Wang September 21, 2019 at 12:47 pm

    7:10 what about the cats’ perspectives? How do you transform that?

  • Reply Biao Wang September 21, 2019 at 12:50 pm

    Take 4 equal sides and form a square. One of the diagonals is “space”, and the other is “time”. Then you can stretch and squeeze the square into rhombi.

  • Reply sail2byzantium September 22, 2019 at 1:11 pm

    Too confusing–esp. with the narration going too fast.

  • Reply Vishal Mishra September 25, 2019 at 2:47 am

    Who in the history of humanity assumed that experimental results have perfect accuracy ? that relative velocity has to be v1+v2 (and not (v1+v2)*m + n where m is close to 1 and n is close to 0 and both could be some arbitrary functions of either v1 or v2 or even both). While special relativity provides a more accurate answer, it is not perfect either (check to 100 places of decimal and you'll find it is in-accurate). An even better theory than SR will turn out to be more accurate in future. A few decades later that would not explain the results and be replaced by an even more accurate theory to 1000 places of decimal. And the cycle of human innovation and understanding of nature will continue to grow more and better over time.

  • Reply Eric Su September 28, 2019 at 11:54 pm

    Prove that Lorentz transformation is valid in physics.
    Submit your paper in PDF to claim an iPhone 11.
    https://sites.google.com/view/physics-news/home/challenge

  • Reply ADKforever September 30, 2019 at 2:42 am

    Henry:

    You need to speak MUCH slower. You have a strident, nasal inflection in your pronunciation, and to compound your unintelligibility, you have a non-standard accent and you speak way too fast.

    The net effect of this is the video is ruined.

  • Reply Double Check It October 5, 2019 at 3:59 am

    I was going to ask about why the red/blue shift happens with light, then I remembered that is a frequency change, not a velocity change.

  • Reply K2's Lab October 5, 2019 at 12:34 pm

    8:08 .. the sheep is moving 50 percent of the speed of light in that example 🤯

  • Reply Harish Aravindh October 10, 2019 at 1:35 am

    I don't know why they named it minute physics …..lol

  • Reply itsmyroad biatch October 10, 2019 at 6:33 am

    Everyone knows time is a cube.

  • Reply tolooleh1 October 11, 2019 at 7:17 pm

    Simple linear algebra yields those equations fast. Less head scratching!

  • Reply Zephyr Cochran October 13, 2019 at 5:33 am

    Cat exist out of time, freely moving, sometimes cuddles.

  • Reply Aprameyan Desikan October 13, 2019 at 5:16 pm

    Are these transformations linear in the spacetime diagrams??

  • Reply Geoff Blankenmeyer October 19, 2019 at 3:08 pm

    Doctor, my brain hurts.

  • Reply William McAlpine October 21, 2019 at 8:09 am

    Is there a resource available to help me understand the equations for when I need to calculate stuff

  • Reply Ginn October 22, 2019 at 3:59 pm

    I clapped my hands whenever I understood something
    then I realized I wasn't the only one in the restaurant.
    xD

  • Reply Zi Why October 26, 2019 at 2:51 am

    Hi. This video series is great! Thanks for doing these. I have one question. At 2:34, you say the angle between the cat's world line and yours needs to stay constant through the transformation. However, later when you show Lorentz transformations, the angle definitely changes. Why is this?

  • Reply Chris October 27, 2019 at 2:46 pm

    You are a very good explainer. Thanks!

  • Reply Suraj Patel October 31, 2019 at 12:12 pm

    I really liked the way you explained the spacetime diagram.. plz. Keep making such videos for us..

  • Reply Mohamed M-B November 1, 2019 at 8:46 pm

    so like light is special right ?

  • Reply comic4relief November 2, 2019 at 3:49 am

    What is a "light ray"?

  • Reply Yaseen :3 November 6, 2019 at 2:33 pm

    As a 13 yr old I have literally no business watching this

  • Reply Amna Salman November 7, 2019 at 1:09 am

    You're amazing! Thank you!!! Keep up the great work ✌🏼

  • Reply who-man ? November 8, 2019 at 5:09 am

    You changed the meaning to suit your narrative tho the lines and there meaning one the line was the subject the next the position the line was on was the subject changing the definition doesn't make it right

  • Reply Nacho Medina November 8, 2019 at 1:24 pm

    sell us the freaking thing!

  • Reply Gowri Ganesh November 9, 2019 at 4:58 pm

    Hi,
    I'm a high school student looking into making the "space-time" globe to help explain the theory of relativity for my final physics project.
    I was wondering if there is any instructions/resources I could use to make it.
    Thanks.

  • Reply Vojtěch Tax November 17, 2019 at 7:00 pm

    The speed of light worldline not moving in the transformation reeks of eigenvectors (thanks 3b1b, just today watched the series on linear algebra)

  • Reply WtF JoK3r November 18, 2019 at 11:11 pm

    finally comment section without indians asking for likes

  • Reply Peter Lilley November 19, 2019 at 4:56 pm

    Fascinating. This is monumental for science, and it ought to be a staple of education for all future generations of grade school and curious discoverers, all of which who, with your partnership with Mark Rober, will break through into the future foundations of theoretical and practical physics.

  • Reply Hector Athan November 19, 2019 at 7:25 pm

    299792458 meters

  • Reply erdi özyıldırım November 20, 2019 at 10:19 pm

    Your animations are brilliant but can you just say the things more slower to be more comprehensible. Thanks for all stuff.

  • Reply erik zalan szabo November 21, 2019 at 4:37 pm

    6:40 so if something would move with the speed of light, it would move with the speed of light from any prespective?

  • Reply Bhahubali Ashish November 23, 2019 at 1:53 pm

    Dear viewers if you didn't get the feeling behind squeezing space-time then it not your fault…
    I will suggest you to watch first 5 videos from playlist of essence of linear algebra by 3blue1brown.

    And see the magic….

    Videos are short and awesome 😃😃

  • Reply Justa Fool November 29, 2019 at 7:43 pm

    SR theory is stupid and wrong. Looking at something from a different perspective DOES NOT change the event being looked at! There is only ONE event, your point of view is never going to change this fact. Get over it, SR is crap.

  • Reply Sauron Gorthaur November 29, 2019 at 11:08 pm

    I had no idea that the Youtube community is so connected, that 3blue1brown knows minutephysics knows Mark Rober knows Mr Beast and etc. It's really cool to think about!

  • Reply chzidm November 30, 2019 at 10:28 pm

    3:40

  • Reply Jonathan Ciesla December 3, 2019 at 11:49 pm

    Lorentz transformations are special frequencies TWICE talked about in so special songs lol.

  • Reply Satou Kazuma December 7, 2019 at 12:58 pm

    is sound's speed constant in the same way that light is?

  • Reply Justin L December 7, 2019 at 7:09 pm

    7:33 More on this Later,

    For anyone wondering.

  • Reply Jacek R. December 10, 2019 at 7:57 pm

    I get it, because time is relative, you can still call yourself minutephysics, because from moving frame of reference, even longer video last one minute, right? 🙂

  • Reply Ezequiel Ghiena December 14, 2019 at 1:33 pm

    So that mean that the Lorentz transform is a Linear Transform where the vector corresponding to t=1,x=c is an eigenvector?

  • Reply Vladimir josh December 14, 2019 at 1:53 pm

    3:17 — (4,0) (4,2) ?????? Do westerners write it (y,x) and not (x,y)??
    Isn't the (x,y) order the standard one??

  • Reply John Nicholson December 23, 2019 at 4:16 am

    @4:21 note the time zone change in the plane.

  • Reply Nima Talebi December 24, 2019 at 1:35 am

    An implementation of this brilliant idea (spacetime globe/cuboid) in desmos – https://www.desmos.com/calculator/waksurlhix

  • Reply Patrick Green December 29, 2019 at 12:34 am

    Hang on bro, you fkn INVENTED that thing? And your working for youtube?!?!?! Not to diminish you cuz your work is brilliant! But WOW!!!!!

  • Reply Brendon Saunders December 30, 2019 at 4:37 pm

    Where can I get a time globe?

  • Reply Chemsdine Sidha December 31, 2019 at 9:18 pm

    Magnifique !

  • Reply JOHN M.V January 1, 2020 at 4:15 pm

    What is moving ? watch…
    https://youtu.be/A3SSf-PoBg4

  • Reply David Bárta January 4, 2020 at 4:53 pm

    Great video. It is better to teach intuition, not equations and your video does exactly that.

  • Reply Just Saying January 7, 2020 at 5:37 am

    What if you want the perspective from something going the speed of light?

  • Reply Yip Shing Ho January 7, 2020 at 7:09 am

    I hope more school would focus on theories rather than numbers in entry level courses, it makes things way more interesting.

  • Reply Vamp Sal January 8, 2020 at 3:40 am

    Amazing

  • Reply Mickeyislowd January 8, 2020 at 10:57 am

    Is the speed of light 'constant'..? There is now a few videos up doubting this. They say the speed of light has been measured at different speeds which was then averaged out to the 186,000 miles per sec so they could define the length of a meter rule. I don't know if they are valid or not so could someone throw some light upon all this, no pun Intended..lol

  • Reply אייל תדמור January 8, 2020 at 9:31 pm

    this episode is when things start to get interesting

  • Reply jhcode January 10, 2020 at 2:24 pm

    You are a hero among us, a groudlayer of how to teach! You might be very well a keystone in the human development. As explaining it simply, you spark the interest to study. Great job and thanks! #TeachersCanLearn

  • Reply scurvofpcp January 11, 2020 at 1:24 am

    I don't know why this channel keeps falling off of my subscriptions list.

  • Reply Sparkymax January 11, 2020 at 2:06 pm

    Tesla said the following on the theory of relativity in a 1935 New York Times interview:

    "The theory, wraps all these (errors) and (fallacies) and clothes them in
    magnificent (mathematical garb) which fascinates, dazzles and makes
    people blind to the underlying errors. The (theory) is like a beggar
    clothed in purple whom (ignorant people) take for a king. Its exponents
    are very brilliant men, but (they are meta physicists) rather than
    scientists. (Not a single one of the relativity propositions has been
    proved)."

    Einstein was a Fraud backed by Rome's loyal JESUIT'S!!!

  • Reply Sal Ev January 11, 2020 at 3:29 pm

    Time speed is not constant and it is equal to speed of light. Speed of light is constant relative to speed of time. Time is relative and the moment is constant but the moment has its movement by time. Moment is passing by with time but actually time passing by from moment.
    We know that general relativity exists.

    Big BUT.

    Each and every information and its meaning is not relative, against meaning of general. There is no such thing as “relative information” but reality is relative.

    General certainty is our constant: which not proven.

    Isn't it silly?

    I didn’t another higher relativity above general relativity. I meant by general certainty. I did it and it is still certain.

    Humanity forgot to define what human is.

  • Reply CheshireCat January 11, 2020 at 4:49 pm

    "Assume the cat moves at a third of the speed of light" that is one speedy little kitten

  • Reply Dave B January 11, 2020 at 7:02 pm

    The time globe should be called the Lorentz abacus.

  • Reply Xintong Bian January 12, 2020 at 11:29 am

    you speek at the speed of light, had to check my youtube playback speed setting ><

  • Reply Ashneel Chandra January 12, 2020 at 2:16 pm

    Thanks for the very informative and easy to understand video on Lorentz transformation. This concept is much clear to me now after watching this. Keep up the great work!

  • Reply Nicola Ristè January 12, 2020 at 2:43 pm

    Did you by accident swapped the first cat and ray of light at 9:55? Or am i stupid and just didn't get anything of the whole thing?

  • Reply Just Dude January 13, 2020 at 9:24 am

    How to look from perspective of light

  • Reply onlyme0349 January 13, 2020 at 6:02 pm

    I just find it interesting how you're directly squishing space to make this work

  • Leave a Reply