Basically we are talking about pole barn paradox of Einstein. Fundamental is Lorentz length contraction. The faster the speed of the object te more contracted it appears. So there is a pole there is a barn and a person. From perspective of pole, barn appears to be contracted and pole doesn't fit from the perspective of barn pole appears to be contracted and does fit. From perspective of a person standing outside pole appears to be contracted and fort. Note that pole travels at 99 percent speed of light and we cam use formula of length contraction. Basically I am a curious student trying to learn this relativity and want to know from experts whether or not I am right

Edited June 27Jun 27 by Spryzen

There’s a little more to it. The ladder doesn’t “appear” shorter; in that frame the length actually is smaller. Length is relative. There is no absolute frame where it has a “real” length - relativity is not an illusion. (this is a common conceptual issue with people learning relativity). In any given frame, some things are at rest, and others are moving. Certain properties of each thing have different values, depending on the frame

The missing bit of this paradox is that the doors opening and closing. The pole/ladder doesn’t fit with the doors being closed at the same time, but owing to relativity, the doors aren’t closing/opening at the same time in all frames. They close simultaneously in the barn’s frame, which means that’s not simultaneous in the ladder’s frame.

1 hour ago, swansont said:

There’s a little more to it. The ladder doesn’t “appear” shorter; in that frame the length actually is smaller. Length is relative. There is no absolute frame where it has a “real” length - relativity is not an illusion. (this is a common conceptual issue with people learning relativity). In any given frame, some things are at rest, and others are moving. Certain properties of each thing have different values, depending on the frame

The missing bit of this paradox is that the doors opening and closing. The pole/ladder doesn’t fit with the doors being closed at the same time, but owing to relativity, the doors aren’t closing/opening at the same time in all frames. They close simultaneously in the barn’s frame, which means that’s not simultaneous in the ladder’s frame.

So it means that it has no real apparent length. It all depends on frame of references in relativity of simultaneity right?. And I have a difficult time understanding that closing and opening doors, so I left that part out. Could you please explain?

5 hours ago, Spryzen said:

So it means that it has no real apparent length. It all depends on frame of references in relativity of simultaneity right?. And I have a difficult time understanding that closing and opening doors, so I left that part out. Could you please explain?

“Apparent” is the wrong description. In the ladder’s rest frame it might be 5 meters long, but in the barn’s frame it’s 1m long. It has that length in that frame.

It might be easier to get the concept with another relative property. In its rest frame, the ladder has zero kinetic energy, because it’s not moving when you’re in that frame. But in the barn’s frame it has a nonzero kinetic energy, because it is moving relative to that frame. There is no kinetic energy that it inherently has, and having KE is not an illusion - it doesn’t appear to have KE, it has KE, as a collision will certainly demonstrate.