I Never Understood Why Space Shrinks as You Approach Light Speed... Until Now

Timestamps:
00:00 Quick recap: Why we can't achieve speed of light
00:50 Do we reach 'c' from space ship's perspective?
2:41 Shouldn't earth reach 'c' as seen from space ship?
4:47 Fundamental rule of relativity
7:31 Discovering Length Contraction
12:26 Length contraction formula
14:14 Evidence for Length contraction
15:25 Einstein says Earth is flat
18:18 You cannot reach speed of light

According to special theory of relativity, a constantly accelerating space ship can never reach the speed of light. Because, due to time dilation, the acceleration slows down and approaches zero, as the speed of the ship approaches c. Remember, it all comes from the postulate that speed of light is the same in all reference frames.

But, you asked what does it look like from the space ship's perspective? In this video, we will tackle just this. We will discover length contraction and why we STILL can't reach light speed.

Link to previous video:

All relativity episodes in sequence

This video was sponsored by Brilliant

[BlyatifulButter]

You are literally expanding the frontiers of us viewers’ knowledge with such concise yet intuitive explanations. You have my utmost respect.

[gcangur]

Mahesh you are inspiring young people while at the same time re-educating older folks. Perfect.

[thetruextremeicon]

I love the way you are able to use your humor and conversational style to make these advanced topics more understandable and accessible.

[Albtraum_TDDC]

Another way to think of it is Length contraction. As you fly in your spaceship and get close to light speed [c], it will appear to become shorter to outside observer.
But also, for you inside the spaceship, you will see the Universe contract in your direction of motion. So for example if you are heading for another star 87 light-years away at 87% of c, it will seem like it's only 43.5 light years away for you. Instead of 100 years to go there, you will only count 50 with your onboard clock.
And if you edge close to c, the distance will become infinitely small. In the end the whole 3D universe will be compressed to a 2D plane for you. Imagine that!
To joke around a bit, if you could go over c then maybe you could burst out of this universe and enter a different kind of universe, where perhaps the lowest speed is c instead of the top speed there. OK OK this doesn't make as much sense, but, feel free to give your ideas on this.

[GokulRaamthelegend]

Absolutely fascinating, Mahesh!
Each video in your special relativity playlist is helping me grasp the idea that our current physics theories aren't necessarily right or wrong; rather, we embrace and utilize them because they effectively describe and explain the phenomena occurring in the universe.

[andymccracken]

If you can find a way to show how curved spacetime produces gravity, in an intuitive way, that would be really great.

[snaatanraina]

Sir, Can you make a video on misconceptions about electricity I tried to understand the transfer of energy in wires from other channels but it was hard and some of those concepts are still quite weak.

[nicholasbutler]

This is the first I’ve seen of your channel but if your other content is at all similar in content and quality then this has to be the best algorithm based recommendation I have ever received on YouTube. Thank you!

[sendintheclowns]

Great job explaining a very difficult aspect of General Relativity that is hard to grasp without doing the math.
You have a great gift at explaining things intuitively, your students are very lucky to have you as their teacher.

[arthurandrade]

Wow, I'm speechless. This is the second video of yours I've seen, and you just appeared out of nowhere on my YouTube. I'm truly moved. Throughout my entire life, I've always been very critical of teachers' didactics, especially when it comes to their views on teaching and, above all, the search for the why of things, the real reason behind mathematics, physics, and everything else.

And for the first time, I'm seeing a teacher explain things in such a fluid, passionate, and direct way, questions I've always had, questions that have been eating at me because they seemed like unanswered questions. No one wanted to discuss them or they didn't understand the question I was asking. Your teaching is truly exceptional, and I’m genuinely moved.

I deeply admire you, even though I’ve only watched two of your videos. The passion for searching for the why of things is amazing. Congratulations, really!

[HopkinsViorel]

I have one question about the speed of light, but first, I would like to ask something about changing frames of reference.

Imagine I stand up and start rotating around my own axis; could I change the frame of reference to assume that I'm standing still, and the universe is the one spinning around me? I know that rotation is a motion which involves acceleration, so this non-inertial motion could prevent this. If that's the case, then my question is answered right there.

But if we can apply the change of frame of reference even in this situation, let's do it. In this case, I am not the one rotating, but everything else but me. This would mean that, from my frame of reference, a chair located 1m away from me would be describing a circular motion, drawing a 1m-radius circle around me, right? Now, let's consider something further from me, like a galaxy on the edge of the visible universe, millions of light-years away:
This same galaxy would be doing a circular motion around me, drawing a circle with a radius of millions of light-years. Consider that it takes 1 second from me to turn around; from my frame of reference, that would mean said galaxy described a circular motion around me in the same 1 second, but if we try to calculate the circular path it took to do so in this single second, considering it's a circle with million light-years of radius, it surely would mean the galaxy moved faster than the speed of light, at least from my point of view.

As I said earlier, a possible answer for this scenario is to understand that my circular motion isn't inertial, so such a change in the frame of reference is not allowed by special relativity. Is this the case?

[ghegogago]

That's very high quality content. Would love to see such a high quality explanation of the twin paradox: why only one of the twins gets old? Pls I didn't understand that even by watching a lot of other videos. By the way, I've clicked the subscribe button at first glance of this wonderful channel!

[Ifyoucanreadthisgooglebroke]

I've never seen this explained so plainly before.

I still can't wrap my head around what happens when there are multiple ship's and a platform's perspectives to all take into account. Here is the scenario:
Ship A is traveling at .75c.
Ship B is traveling at .75c in exactly the inverse direction.
Observer C is measuring the speed of both ships from a third location.

How fast are the ships moving from one another's perspective, and how fast are they moving away from one another from any third perspective such as that of Observer C? If the ships sent a signal to one another using a means of communication that travels at the speed of light, when would it get from one ship to the other? If the ships had an entanglement based means of communication as well, and communicated to one another via both methods, and measured the difference in how quickly the messages arrived, what would the difference be?

Because it still seems to me that there could be some kind of, lets call it "3 Roentgen", situation going on around the measurable vs calculable vs practical c given that all the math insists that ship A and B are traveling apart at...infinitely close to but not quite c. Yet if those ships stop after a year, and set up colonies, and someone builds a super telescope to view signs of the sister colony with, then surely they better know not to expect to see anything of the other colony just one year later from the founding of their colony. The sister colony is located 1.5 ly away, and was only founded a year ago. Well, except that we can prove that they could only have moved 1ly away from one another in 1 year. Shit.

It appears to me to be knots all the way around once you consider the speed from those three different points of reference, and I've yet to hear it untangled in a way I could follow. It seems like Einstein's train didn't take into account the perspective of the lightning bolts, nor the possibility that they might try to compare notes with one another throughout the process, nor what happens after said note-comparing objects in such situations stop and cease to be subject to the kind of length contraction that occurs at meaningful fractions of c.

[ChronicWhale]

Thank you so much, you're an excellent teacher and this channel is the only one which finally breaks some mental blockers, and allows me to wrap my head around relativity

[kevinhightides]

This is quickly becoming my favorite physics channel. Great work, Mahesh! It's 1am, I have to work tomorrow, and I just played a gig (3 hours of high energy rock), but what's this? An explanation of length contraction? Meh. I'll sleep when I'm dead. Bring it on!

[seconds]

Best explanation I've seen yet.... Understood it easily and covered all my confusions

[AmerAlsabbagh]

Thanks, it was great explanation, yet, it missed some important explanations like:
- Why the speed of light is constant?
- When the clock pointer moves in the direction of the movement it gets understandably slower, but why it does not go faster in the other direction?
- Why can't we consider all the movements relative to the center of the universe and get rid of the whole relativity jargon? Or, can we?
- What is the relation between relativity and Higgs Bosons?
- Are you really saying space is changing, or only our perception of it? And that could mean for the center of the universe?
- What is the relation between all of this and the energy preservation concept in a closed system? And what will happen if we discovered someday that our universe is not a closed system?

[SohamDamle]

I personally hated physics all my life, just becoz of tons of formulas and ridiculously long calculations, I'm 18 now and preparing for Neet ( a premedical entrance test in India ) and I do like the concepts of physics like we got Motion 1D and 2d, Newton's Laws of motions, waves etc . AND I MUST SAY I WATCHED 5 OF YOUR VIDEOS JUST BECAUSE HOW WONDERFUL THEY ARE, it's a piece of art really, and watching this motivated me to go study some physics for my upcoming test 😂 😅b, TYSM bhaiya ❤❤❤❤, LOVE FROM INDIA

[Arxces]

Makes you wonder: how does light reach the speed of light?

[allmytacks]

Thank you so much for your videos. This is what i was looking for for years, truly. Intuitive understanding of science is really fundamental. If it possible, could you make some intuitive explanation of twin paradox?