Time.timeScale

Description

The scale at which the time is passing. This can be used for slow motion effects.

When timeScale is 1.0 the time is passing as fast as realtime. When timeScale is 0.5 the time is passing 2x slower than realtime.

When timeScale is set to zero the game is basically paused if all your functions are frame rate independent.

Except for realtimeSinceStartup, timeScale affects all the time and delta time measuring variables of the Time class.

If you lower timeScale it is recommended to also lower Time.fixedDeltaTime by the same amount.

FixedUpdate functions will not be called when timeScale is set to zero.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void Update() {
        if (Input.GetButtonDown("Fire1")) {
            if (Time.timeScale == 1.0F)
                Time.timeScale = 0.7F;
            else
                Time.timeScale = 1.0F;
            Time.fixedDeltaTime = 0.02F * Time.timeScale;
        }
    }
}