The 4th Dimension in Relativity isn't Time - it's Space.

Our reality is a 3 + 1 pseudo-Riemannian spacetime manifold whose intrinsic curvature manifests itself as gravity, right? Well no, because descriptions are not reality, and math is not physics. Indeed, when taken at its most literal, face-value, what the "fourth dimension" in relativity actually describes is a very far cry from what most modern science communicators would have you believe. Join us to discover the implications of how doing actual physics, and not just math, can lead to better understanding of the relativistic puzzle -- as well as open up some exciting new theoretical possibilities.

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[IndependentPhysics]

Unfortunately special relativity doesn't actually tell what (ontological) time really is, but rather how light behaves in time with respect to space.

[erenakker]

I enjoy your videos; however, they often conclude with a cliffhanger that the subsequent video neglects to address.

[JH-lesd]

Velocity*time isn't "space" in the way we usually think of it (i.e. it isn't *extension*), it's *displacement*. Problem is displacement and extension have the same units, and this had led to great confusion that they are thus the same thing. This video does a good job elucidating this.

[chrimony]

One day I will meditate on this until I reach enlightenment. In the meantime, in the bookmarks it goes.

[MrTheophilus]

The dimensionality argument is bogus. We don't need to write the metric interval in terms of spatial units. It can also be represented entirely using temporal units. Another convention for the space-time interval is all time units so that DS squared equals DT squared minus dx squared divided by the speed of light squared for each spatial dimension. We then measure distances in units of years. Yes. That's the well known light years for distance. So using those units we could say space-time is really a time time continuum

[EricKolotyluk]

It's been over a century that Einstein published his theory of General Relativity, but few people grok what it means. However, the explanations of General Relativity continue to evolve... those people evolving those explanations are working to create a world where more and more people can appreciate such beauty of nature, and they should be applauded for trying to build such a beautiful world of knowledge and understanding.

[nHans]

Sure. But that fourth "spatial" dimension — obtained by multiplying _t_ with _c_ — is not like the other three. In fact, when I studied Special Relativity — admittedly a long time ago — the fourth dimension was represented by _w_ = _ict, _ where _i_ = √(-1). So while _x, y, _ and _z_ represented "real" 3D space, _w_ was "imaginary" space. The math worked out just fine. The Lorentz transformations — space contraction, time dilation etc. — came out naturally and beautifully as rotations in this 4D space comprised of _x, y, z, _ and _w_ = _ict._

[Astrophysics]

Your description I think is attractive but at he sametime does not add something deeper or new to our understanding to nature or the theory it self. After all how you see it, is just a matter of taste. I believe your way of viewing it involves us with the philosophy of physics and the world views there are like realism, instrumentalism, anti realism...etc.

That is how I understood it before, and that is why I see it fine:

We are constantly traveling through time at the speed of light. By dealing with time as a kind of distance or space dimension, we can conceptualize and measure it more easily and fit into the equations. This approach allows us to incorporate it into equationstoavoid comlexity that would be faced if there was a different units in the equations.

After all when we try to understand something, we often compare it to what we already familiar with, and look for patterns to make sense of and describe it. (Just like when gravity viewed as force it worked well, while inaccurate, and now we view it as curvature, its a deep precise description but its the way we view and see it not the true nature of it! curvature descrption seems to fit the behavior of gravity, it does not neccessarily means that is how it is! Gravity might be a particle that exhibits features that makes it look like curvature!). The point is we dont know. we onlycn describe according to our cognitive nature and categories we use to view the world.

That is why I think viewing time as a space dimension to be fine and work very well. It makes time easier to deal with mathematically and conceptually.
If we look at the challenge with quantum mechanics is similar: there are no direct analogies from everyday life to help us intuitively grasp and understand its phenomenon, which makes it harder and almost impossible to follow intuitively.

[ShimrraShai]

Also, 6:08ish - that is an interesting question as to whether it is about "spacetime" or about "dynamics" - indeed the whole point of the Lorentz symmetry is that it is a symmetry _of dynamics._ So we could ask whether dynamics defines spacetime or spacetime provides symmetries dynamics is required to respect. In fact, this is not trivial, because we could easily write up on paper laws for an imaginary universe where some laws follow Lorentz symmetry and some break it. (The thing as a whole would then break Lorentz symmetry; the point is that it is not illogical, just not so-far what the universe we live in seems to operate like.) Hence, this is a matter which has to be settled by experiment, i.e. to ask whether the real world actually works this way. And this brings up a crucial point, which is that where you say here about it having to do with "light" - indeed, that is an experimental contestation, i.e. does the behavior of these light clocks and the like translate to other matter? And in fact it does (so far), it translates to _every_ known physical law, not just light moving but electrons moving, even particles decaying - every "temporal" process seems to follow the Lorentz symmetry. And I would argue it is _this experimentation_ that is the best "buttress" for the "spacetime interpretation" of the Lorentz symmetry. But ultimately, yes, spacetime is a modeling entity, and there may be other/better/different ones. But still, there is nothing _wrong_ with it in any formal/logical or, so far, any empirical sense, even if it may make some sense to be aware of this.

[richsalinas]

I don’t have a physics education or background so most of what dialect is explaining is beyond my comprehension. I do however enjoy when a new Dialect video pops up on my feed. 🍻 cheers to the team on another great vid. The animations keep getting better!

[minotaurbison]

1:42 MOOOOMMM the C fell off my axis again!

[Nobody_]

There is 3 major flaws to Einstein's "light shined from the floor to a reflective mirror on the ceiling" thought experiment (ETE):

1) As you approach the speed of light (C), the light/laser does not return to its source on the floor. Why? Because the light wave is emitted in concentric circles at C independent of the observer's motion. In fact, it can be proven, that as you approach C, the light/laser will return to an offset position on the floor behind the source in the direction of motion (DoM).

2) For the same reason as above, the *distance* light/laser travels from the source to the ceiling increases before it hits the ceiling. This means that it is not time that is dilating, but distance increasing instead. To ensure the same distance travelled by the light/laser to calculate "time dilation" as ETE and that the light/laser returns to the same point as the source for the moving observer, you would need *vertical/perpendicular contraction* to the DoM in addition to the "Lorentz contraction" in the DoM. There are already papers published on this subject.

3) Unless one of the 2 observers accelerates or decelerates and meets the 2nd observer, none of the time dilation results can be verified, even for particles. This means, that the examples of particles taking longer to react to something (like muons coming to closer to earth's surface), or particles having a higher energy at velocities closer to C, can only be detected when the particles collide and react, at which point they are no longer moving close to C, which negates time dilation as the reason for the differences in reaction/collision energies while they were moving near C.

[shpensive]

Dialect is the uploader I get most excited about. Tackling these questions that are so important and neglected, with the rigor to get it right, the bravery to echew convention, and a beautiful, thoughtful presentation!

[dariuslegacy]

I think some people have taken the whole "physics is the language of the universe" as gospel and forget that a lot our models are simplified representations of things and their relationships as we measure them, not as they actually are. It's clearer with the Copenhagen convention but even Newtownian and Einsteinian Physics ultimately rests on conventions for interpreting equations. The Post-modern in me wants to say the only things we can meaningfully say exist are those things that are in the domain of our experience, any concept of time outside what we can try to measure with a co-moving clock (psychological time) is arbitrary. Though I do find the 4 dimensions of Space-space as odd yet unique in its framing of relativity, which can only help deepen our understanding.

[TerranIV]

I know that anyone can decide to call a lot of things a "dimension, " but time is a literal dimension in GR (as in time is on the same level as the x, y, z dimensions). I think it is perfectly valid to say that it is a physical dimension, but it is NOT just the dimensions between the ends of the light clock. Remember, velocity is relative so you can't say which observer is "moving, " all you can say is that one is moving relative to the other. The observers are displaced in TIME as well as distance.
If you want to call the Time dimension "spatial" (i.e. "the fourth dimension") that is exactly what Einstein was getting at. To your point, ALL time may not be from motion in that dimension (i.e. a ticking of a local clock is not necessarily spatially displaced), but you could frame it that way, and most physicists would probably argue that time itself is caused by all matter moving at a constant c velocity in a direction of that spatial dimension.

[landsgevaer]

You can call that dimension space, but then it is a special kind of spatial dimension that is different from the other three. And that different type of dimension we call time.

Aaaand we're back.

[ramusaladi]

How can you create such tremendous animations bro hats off to you .by the way which software could you use ?

[aclearlight]

Bravo! I am delighted to have re-re-discovered the treasure trove head-righting clarity and thoroughness which you build into your presentations. Great work!

[JuliusBrainz]

What you say here is nothing new. It does not take 12 minutes to explain that c is there for dimensional reasons, that ct is the distance that a light beam travels. But just because it has a dimension of length does not mean it is space. Like a wavelength is not space, like the length of arc is not space, distance travelled by an object is not space. And it is not illiteracy to call ct the time dimension. Because we need to distinguish the nature of the dimensional. Spatial dimensions have the same nature, while the time dimension does not. So why should we confuse ourselves by calling space. I refuse to call a distance travelled by an object the Euclidean space which is what we usually call space in flat case.

[ffs]

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