Most of Relativity Isn't Common Sense... Except This Bit - Relativity... Relatively Quickly Ep. 1

Welcome to Relativity... Relatively Quickly - a series looking at the most basic concepts of three theories of relativity. This is the first episode - what is relativity?

In this video, we start from the beginning. We look at what relativity means, and how it discusses the relative motion between objects. From the perspective, or reference frame, of one observer, they are stationary and everything else around them can be either stationary or in motion. In this video we see how an asteroid moving past a spaceship has motion according to people in the spaceship. However from the perspective of the asteroid, the spaceship is moving and the asteroid itself is stationary.

Both reference frames are correct from their own perspectives. Since we are studying constant speed motion in a single direction, we won't look into too much detail about inertial reference frames, though this will be discussed later.

On Earth, we can think of walking along the ground as being due to us remaining stationary, and the Earth moving beneath our feet. However this is trickier to think about because we always use the Earth as our "stationary" frame of reference. The point is, though, that the Earth moves around the Sun (in the Sun's reference frame), and the Sun moves around the center of the galaxy, and this moves around a common center of mass. There is no one special stationary reference frame.

In this series, we'll study Galilean relativity, special relativity, and general relativity. The first of these is based on "common sense" Newtonian physics, that makes intuitive sense to us. However our intuitions don't work in scenarios that we do not commonly experience as humans. One example of this is travelling at very high speeds (close to the speed of light).

When studying objects moving relative to each other in Galilean relativity, we can use what is known as standard configuration. This is when one reference frame moves relative to another along their shared x (or x') direction with a constant speed v. In addition to this, it is agreed that both reference frames agree on a time coordinate of zero, meaning t = t' = 0, and this occurs when the frames overlap so x = x' = 0.

We jump back and forth between two comoving reference frames and look at how each one would perceive the motion of a third object. We do this by plotting a distance-time graph for each frame. One frame could see the object as stationary, while another could see it as moving! And this is all true without accounting for the spacetime bending weirdness of special and general relativity.

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Timestamps:
0:00 - The basic concepts of relativity: what is it?
2:32 - All the theories of relativity.
3:27 - Big thanks to Wren for sponsoring this video!
5:13 - Galilean relativity and reference frames
7:41 - Standard configuration
8:32 - Weirdness in other relativity theories

#ad this video was sponsored by Wren!

[rampradeep]

Can't wait to see the way you explain the difference between Newtonian gravity and Einstein's gravity

[dhanyamv]

I was waiting for this video for a long Thank you Parth

[darshanpatel]

Really, very Happy for this and very Eager for next one😇
Thanks for

[rampradeep]

Have been waiting for this sir !! Thank you

[anikou]

really enjoy your method of explaining, and the way you do your diagrams! would love it if you did a video on lorentz transformations

[poojaagara]

You explain the concept like we already know it👌👌

[duckslayr]

Too bad you didn't do this video 4 months ago, when my Intro to Relativity class started.

[mathematicalmonk]

Can you make a video of calculus of variation and it's use in physics

[humzahkhan]

Petition to rename video: "Relativity made relatively easy"

[shivalikasharma]

Could you please explain quantum hall effect and spin hall effect ?

[robertrobert]

I'd like you to cover things beyond GR, e.g. theory of superluminal observers (and it's connections to QM) from A. Dragan.

[Pavan_Gaonkar]

Please touch general theory of relativity.

[bradleywalsh]

Parth I would like to hear your thoughts on how Chris "The Brain" views General Relativity and his novel, at least to many, concept of gravity. If you haven't heard of him you should check him out.

[jtpluck]

It would be cool to here a video about dark matter and the math that led up to the idea

[hmlckx]

I'd love to see the difference between General and Special relativity

[ailblentyn]

As far as the usefulness of these examples:
I think taking the person walking on the earth as a reference frame is unintuitive because the person accelerates themselves.
In the same way, the example of the spaceship and the rock is unintuitive because the spaceship has engines and has accelerate itself in the past. Just using two asteroids passing each other in space would be clearer, I think…

[misterlau]

Mkay but the stuff that gets people's head blown is the lots of tensors inside Tensor in general relativity.

Right my witty physicist, G?
Man you know you look way younger without the extra hair but I was used to that look. And if you shave, I guess you will look..
So Young we need to use negative time or a Wick rotation 😂😂😂😂🥺😬😓🤣🖖🤓Cheers!

[vgzvusr]

2:20 Since Universe is expanding, therefore center of mass should be dancing in God know what way because, say, black hole should spiral away from the center, or where Big Bang had happened.

[new-knowledge]

First of all, if you know nothing about physics, then you are in BIG luck. That is because in schools today they have the tendency to throw you off track and confuse the heck out of you. For instance, they tell you that if a truck is going say 50 mph, and someone on the truck throws a ball in the same direction that the truck is going, and throws it at 10 mph relative to the truck, they tell you that an observer standing on the roadside, will see that the ball is moving at 60 mph ( 50 + 10 = 60 mph ). They tell you this even though this is absolute rubbish, since the total velocity relative to the roadside observer, is a tiny tiny tiny bit less than 60 MPH, and that this is the case for a very very important reason. Then after misinforming you in this manner, they then proceed to then say that this rule does not apply to light, and that no matter how fast the truck is going, the light from its headlights will still be measured by the roadside observer, as being the speed of light. But the point that they wanted you NOT to know about in the first place, all to confuse the heck out of you, was that the velocity of 50 mph plus the velocity of 10 mph, does NOT equal 60 mph. Perform Einstein's velocity addition equation, and see it for yourself. Thus, one velocity addition rule applies to both situations, meaning the truck/ball combination situation, and the truck/light situation. But the deceivers tried their best to convince you that these are two separate rules altogether. Anyhow, if you are lucky and know nothing about physics, and thus you have not been deceived by the deceivers, then simply analyze motion to figure out exactly what it is, and bingo, you will soon have independently discovered the special relativity(SR) phenomena, and you will have independently derived the SR mathematical equations at the same time.

[new-knowledge]

PART TWO: Imagine that a God created a 4 dimensional environment that is composed of 3 dimensions of space, and one dimension of time. This is the beginning, and so we will refer to this as being our "Absolute Frame of Reference". Now the big boss places content/objects within this space-time environment, and all these objects that were placed here, are constantly on the move, with each object moving with the exact same magnitude of motion as all others, but of course they can move in different directions within the 4D space-time environment. We will therefore refer to this as a fixated "ABSOLUTE" magnitude of motion. Now, what they heck is the outcome of such a setting that is constructed of these Absolutes ? Well, you will end up with time dilation, length contraction, a strange velocity addition equation, the Lorentz transformation equations, the constant speed of light, and so forth. Funny how they don't say much about this in schools, just to confuse the heck out of you. Instead, they continue to convince you concerning motion, that motion is an effect without a cause.