The universe is not as straightforward as it seems and the speed of light has a lot to do with that. It’s the ultimate speed limit, as nothing in the universe can travel faster than it.

The speed of light is 299,792,458 metres per second, or 1,079,252,848.8km per hour.

So how does it move? ”Light is just pure energy,” explains Dr Ronan McNulty, an experimental particle physicist at UCD who is also a former Young Scientist of the Year.

“Tiny little ‘tennis balls’ that make up the light are actually called photons because they don’t have any mass themselves,” says Ronan “It goes at the ultimate speed limit, 300,000 km per second, and there are some earth-shattering consequences.”

Einstein

Suppose you are in a car and it is travelling at 100km per hour. You throw a ball from the car and it travels at 10km per hour. If someone is outside the car is watching, they will see the ball travelling at 110km per hour.

However, if the car has its lights on, and is going at 100km per hour, the light is not going at the speed of light plus 100km per hour, it is going at the speed of light.

Albert Einstein is responsible for a lot of our ideas about the speed of light. In 1905, he said that the speed of light is constant, no matter where you are. It does not matter if you are moving or stationary when you measure it, or if the light source itself is moving, the light’s speed will always be the same. This is an important part of Einstein’s theory of relativity.

Human speed

So will we ever be able to move at the speed of light?

“Unfortunately, if you have mass, you’re not going to be able to,” says Ronan. “As you try and go faster and faster, what happens is that mass gets heavier and heavier, and if you were to try and go at the speed of light, you’d actually have infinite mass. You can’t have infinite mass, so that’s the real reason why we can’t go at the speed of light. The only thing that can go at the speed of light, is light.”

To measure the speed of anything, you can divide the distance by the time it takes.

SCOPE conducts a special experiment to demonstrate this. At a secret location, Danann eats a bowl of sweetcorn and takes note of the time. The sweetcorn slowly works its way through his system.

Eating speed
First, it travels down the oesophagus into the stomach. Then it goes through the small intestine – which if unraveled would measure about 7m. It then goes into the large intestine, (about 1.5m), before finally coming out the other end.

The sweetcorn takes a total of 21 hours and 18 minutes to pass through Danann’s system.

To work out the speed of your insides, you can do a simple equation:
Speed = Distance
Time

The average digestive system of an adult is 8m long. So, the distance is 0.008km and the time is approximately 21.3 hours. This gives a speed of 0.0003759km per hour, which is 37.59cm per hour - not very fast.

Danann’s insides are pretty normal though – it usually takes about 20 hours for food to pass through the human digestive system.

Learn more:

Read about scientists trying to beat the speed of light

Read about Einstein’s theories on science.ie

Understand the theory of relativity