# Why particle in a box is considered as 1-dimensional ?

1. Jun 30, 2010

### dying_star

I'm new to the field of quantum mechanics and I have got this basic doubt.
The position of the particle in a box is defined by the sine curve. Any position on a sine curve requires 2 coordinates to get the location of the particle having the highest probability at any point of time.
But why is it considered as single dimension ?
(The particle is free to move in the left or right direction, but as we define it by a sine curve it can also move up and down.)

2. Jun 30, 2010

### Staff: Mentor

No, it doesn't move up and down. It moves only left and right, and solution doesn't tell you what is particle's position in terms of (x,y), but what is probability of finding it along x axis.

3. Jun 30, 2010

### dying_star

Do you mean that even if the particle moves in space inside the box, we are interested to know the position with respect top X -axis.

4. Jun 30, 2010

### Staff: Mentor

It is like a bead on a string - it can move only left and right. Thus only x axis.

5. Jul 2, 2010

### AJ Bentley

The vertical axis of the graph is the probability amplitude, not the spatial direction.
It's a graph, not a picture of the box.

It's the same as if you made a graph of the speed of a car starting down a road and stopping. The graph goes up and down - but the car doesn't. The road is one-dimensional.

6. Jul 3, 2010

### zzzoak

If it is used 1-dimentional hamiltonian then the solution depends on 1 coordinate x.
If 3-dimentional then f(x,y,z) is obtained.
It depends on the potential energy if the solution is the product of seperate functions
f(x,y,z)=f1(x)f2(y)f3(z).
Sometimes the form of separate functions is the same and
f(x,y,z)=g(x)g(y)g(z).
So if g(x) is known the 3-dimensional function is known too.
It depends on the definite problems under consideration.