The Rocket & String Paradox

Einstein boards a train and asks, "Does Boston stop at this train?"

Relativity is one of those things that just makes things weirder the more you explore its implications.

There's an alternate version where the string does not break. If both rockets accelerate in unison from their own point of view the string does not break. But to a stationary observer, it would look like the front rocket is more past-like and less accelerated, so the rockets appear closer together, relieving tension on the string.

I'm doing a MSc right now and largely feel like I've seen almost every "wow that's counter intuitive" common physics example. Not much amazes or tricks me anymore. I can say with confidence this properly blew my mind like I was in highschool again. Thank you for that :)

This is wild. I would not have predicted this. But your explanation is so clear that it almost feels intuitive now. Oh, and nice title and thumbnail!

You’re tearing me apart, Einstein!

Engineer: Any real string would break from accelerating its own mass before relativistic effects are important

"In some cases it's also whether you're torn apart, or whether you tear yourself apart." Apparently this guy understands more about life than my shrink.

Title and thumbnail sounds like minutephysics watched Veritasium's video on Clickbaiting. "Do Salt Lamps Work?" "No." 😂

I don’t understand your definition of “accelerates at the same time ” so I can’t follow why there would be any force on the string. The string also accelerates at the same time as the rockets and thus the length contraction works as a function of the velocity relative to an observer. If both rockets are equidistant from an observer, at rest relative to said observer, and that observer reports that they accelerated at the same time, where is the force? In the reference frame of the string, which is really what matters here, both sides started moving at the same speed at the same time. It’s equivalent to holding a rope at both ends and running or spinning. It’s not going to get taut just from the motion. Edit: the replies have made it clear that the question assumes that the ships are not accelerating at the same rate therefore, the “paradox” here is actually to do with the setup of the question. You don’t need relativity to understand that pulling both sides of a string by different amounts will break it. If they accelerated at the same rate, the distance between them will contract at the same rate as the string, and it will not break.

Correct me if I’m wrong but from my understanding so long as the string has mass and the rockets are accelerated at the same time, direction and magnitude, the entire system would shorten length wise which includes the string meaning from an outside perspective the rockets should appear closer together

I remember watching your videos years ago! I never took a physics class in high school and here I am 10 years later at college taking electromagnetism <3 thank you for sparking my curiosity!

But if the rocket at the back accelerates ever so slightly sooner than the one ahead, have you then countered for this space time conundrum?

Taking a page out of Veritasium's book for the title. I like it!

Another note on why everyday objects don't tear themselves apart. The kind of acceleration and speeds we deal with for everyday things is relatively slight. So, it don't take much cohesive forces for everything to stay together. Even when they do experience this kind of tension, they have the strength to hold together. In this thought experiment, the string has no such strength and is torn apart. But, a strong enough string can hypothetically stay together. It becomes an engineering problem when dealing with extreme forces to find the right material that can stand up to the task.

You can consider/create another point of view for "simultaneous": accelerating just enough both ships so the string stays stretched without break. In such case the string would look shorter.

If "[...] both rockets suddenly accelerate at the same amount at the same time..." how can the first one accelerate first? The 1:16 part, which is the core of the explanation, needs further detailing, since it has to break the firm assumptions that we have about our "reality".

Using the premiere feature means I see the video show up now when I am interested in watching, but it's not there. That's already annoying, but the worst part (for you) is that I will forget about the video when it actually comes out. Nobody likes this horrible feature, please don't use it for normal videos

I've seen this video everyday since it was released and I learn something new each time.

Finally a new video! Where have you been, glad you're back :)