# Cosmic Speed Limit

#### Think you can travel as fast as you want? Think again.

For centuries, physicists thought there was no limit to how fast an object could travel. But Einstein showed that the universe does, in fact, have a speed limit: the speed of light in a vacuum (that is, empty space). Nothing can travel faster than 300,000 kilometers per second (186,000 miles per second). What's more, only light can travel at this speed. It's impossible to accelerate any material object up to the speed of light because it would take an infinite amount of energy to do so. So as it turns out, Einstein could never have caught up with the beam of light that captured his imagination as a teenager!

##### Moon Race

How long does it take to get to the Moon? Light travels the 380,000 kilometers (240,000 miles) between the Moon and the Earth in 1.3 seconds. It would take a person more than nine years of continuous walking to travel this distance.

Light: 1.3 seconds
Electron: 2.9 minutes
Space shuttle (orbital speed): 14 hours
Sound (70°F): 13 days
Passenger jet: 18 days
NYC subway car (maximum speed): 220 days
Human (walking): 9 years

##### So why can't you travel faster than light?

The faster an object travels, the more massive it becomes. As an accelerating object gains mass and thus becomes heavier, it takes more and more energy to increase its speed. It would take an infinite amount of energy to make an object reach the speed of light.