Alex McColgan

The barn is not simultaneous, because you can see it across a range of times.

Its length might be contracting, but the dimensional space you see it occupy in time seems to you to be growing.

We do not think like this, but the idea has a beautiful sensibleness to it in a universe of 4D space.

Like when a racing car swerving to the left causes its right wheel to protrude further forward, when you move to the left on our spacetime diagram, it causes the part of you furthest away from the direction of motion to protrude into the future more than the part that's closer.

That's just geometry.

For the record, this seems to happen as a gradient along the whole of the object in motion.

This way of thinking also allows length contraction to conceptually make a lot more sense.

After all, if our pole is in motion and the front of the pole is further in the past and the back of the pole is further in the future, then it makes sense to consider where each part of the pole exists in space during those moments in time.

The front of the pole that exists further back in time

has not travelled as far as the rest of the pole, so the start of the pole is further back.

Similarly, if the back of the pole which exists further forward in time has by then moved further through space compared to the rest of the pole, so the back of the pole is further forward.

What happens when you combine a dawdling front with a further ahead back?

Length contraction.

The only surprise is that it seems that we can see this, in experiments in the Large Hadron Collider and other places.

Somehow, we are seeing across a cross-section of time.

So, it works.

It just feels like it shouldn't.

You might think this is a little out there, but consider.

What would an object that didn't exist in all the same moment in time look like to you?

Could you tell it apart from any other object?