# Length contraction

#### Nforce

If we are on space ship which is travelling with the speed near $$\displaystyle c$$. And there is an observer on the earth who is watching the space ship. Who would experience length contraction and why?

So if there is a table on the space ship. And we measure it's length when travelling with the speed near $$\displaystyle c$$. From the theory of relativity it should be shorter then the original length. But what would the observer on the earth see? If there is a window on the space ship and the observer on the earth can see trough the window this exact table when travelling with the speed near $$\displaystyle c$$. What will he see?

#### HallsofIvy

Each observes the other as "contracting". That is, a person on the earth would see the space ship contracting while a person on the space ship would see the earth contracting, Neither would "experience" contraction. Each person has speed 0 relative to himself.

"So if there is a table on the space ship. And we measure it's length when travelling with the speed near c. From the theory of relativity it should be shorter then the original length."

Who do you mean by "we"? If a person on the space ship measured it, it would have exactly the same length as it always had. Its speed is 0 relative to that person. Assuming a person on earth could see it, it would appear contracted in the direction of travel.

2 people

#### Woody

A key term in the Theory of Relativity is Relative.

All the weird effects are only apparent when the observer is moving (fast) relative to the thing he is observing.

Or in the case of your example when one observer is moving (fast) relative to another observer.
Note that in this case both observers are moving (fast) relative to each other,
so both see the other one contracting, but to themselves they are completely "normal" it is the other that is exhibiting "relativistic weirdness"

2 people

#### Nforce

Thanks, now I understand.