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What happens when you drop a bowling ball and feather at the same time? The answer seems pretty obvious, with the latter falling slower due to air resistance.

But in the latest episode of Human Universe Professor Brian Cox explained how, in the absence of air, both fall at the same rate owing to the laws of gravity.

To prove the theory he used the world's largest vacuum chamber, which normally tests spacecraft, to drop a bowling ball and feather from a great height in space-like conditions.

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In the latest episode of Human Universe Brian Cox tests the laws of gravity . To do so he travels to the Nasa Space Power Facility near Cleveland, Ohio, the world's biggest vacuum chamber, and drops a bowling ball and feathers (shown) - which fall at the same rate

The video is from the fourth episode of Brian Cox's Human Universe, which looked at our origins and place in the universe.

Professor Cox visited Nasa's Space Power Facility near Cleveland, Ohio to investigate theories of gravity from two great scientific minds: Galileo Galilei and Isaac Newton.

Both theorised that, in the absence of air, objects would fall to Earth at the same rate.

This was famously proven on the lunar surface in 1971 by Commander David Scott during the Apollo 15 mission.

On the moon he dropped a feather and hammer and watched as they fell in the same time, proving that all objects fall at the same rate when air resistance and other forces do not come into play.

To create an environment devoid of air, similar to the conditions encountered in space, the vacuum chamber Professor Cox visited is capable of pumping out 30 tons of air until there are just two grams (0.004lbs) left.

Originally built in 1969 to test nuclear propulsion systems, the chamber is now used to test modern spacecraft - but Professor Cox used it to test this more humble although still impressive experiment.

First Professor Cox raises a bowling ball and some feathers high into the chamber, before the air has been removed, and drops them to the floor.

In this initial experiment the bowling ball drops straight to the ground whereas the feathers float, owing to the air resistance in the room.

He alludes to the earlier experiment by Galileo that tested the same hypothesis.

'Galileo's experiment was simple,' he explains. 'He took a heavy object, and a light one, and dropped them at the same time to see which fell fastest.'

But, while Galileo's experiment proved two similarly shaped objects would fall at the same speed despite being different weights, he didn't have access to a vacuum chamber in the 17th Century to conduct Professor Cox's more extravagant experiment.

Namely he wasn't able to show that two objects of vastly different weight and surface area, in this case a feather and a bowling ball, would fall at the same rate.

Brian Cox proves laws of gravity in world's largest vacuum...

Nasa's Space Power Facility (shown) was built in the 1960s to test nuclear propulsion systems but is now usually used to test spacecraft. It was made out of aluminium to cope with the radiation but needs an outer concrete 'shell' to make sure it is strong enough to hold a vacuum inside

As the team gears up to perform the experiment the giant door of the chamber closes and the 800,000 cubic feet (22,650 cubic metres) of air is pumped out in a process taking three hours.

'But once it's complete there's a near perfect vacuum inside,' said Professor Cox.

Standing with the control team, one of the engineers presses a button that again releases the bowling ball and feather from a height, as in the first experiment.

But this time, in a moment that amazes the team that Professor Cox is with, both dramatically fall at exactly the same rate.

'They came down exactly the same!' exclaims one of the team with Professor Cox.

'Holy mackerel,' says another.

Professor Cox's reasoning for conducting the experiment is not just to prove Galileo and Newton correct. It's to prove a more interesting hypothesis put forward by Albert Einstein in the 20th century.

Galileo's theory of gravity was famously proven on the lunar surface in 1971 by Commander David Scott during the Apollo 15 mission (shown). He dropped a feather and hammer and watched as they fell in the same time, proving that all objects fall at the same rate when air resistance and other forces do not come into play

'Isaac Newton would say that the ball and the feather fall because there's a force pulling them down: gravity,' he said.

'But Einstein imagined the scene very differently.

'The "happiest thought of his life" [as Einstein called it] was this; the reason the bowling ball and the feather fall together is because they're not falling.

'They're standing still. There is no force acting on them at all.

'He reasoned that if you couldn't see the background, there'd be no way of knowing that the ball and the feathers were being accelerated towards the Earth.

'So he concluded they weren't.'

This slight tweaking of Newton's earlier theory enabled Einstein to more accurately define his own Special Theory of Relativity.

This regards the relationship between space and time but one of its conclusions is that nothing can travel faster than light.

Apollo 15 commander completes Galileo experiment on the Moon

Albert Einstein's Special Theory of Relavity showed how space and time interact, and also looked at the effect gravity has on the universe. It was first proposed by Einstein in 1905. Illustrated here is Nasa's Gravity Probe B spacecraft, launched in 2004 with a twin spacecraft to prove Einstein's theories

Under Newton's theory, though, it was thought that changes in gravitational force would be instantaneous - clearly breaking the laws of physics.

But Einstein proposed that the objects were not falling at all. Rather, if you were to replace one of the objects with, say, a person in a box, it would be impossible for the person to know they were falling.

And this is what Cox meant with his final statement. From the frame of reference from one of the falling objects in the vacuum it would be impossible to know what forces are acting.

This became known as the 'Principle of Equivalence' and, in essence, it showed that mass was independent from other forces like gravity.

Long story short? Cox's experiment proved the theory of gravity that Einstein called "the happiest thought of my life".

Professor Cox showed that, in the absence of air, falling objects are essentially 'at rest' and it is not possible to know if one of the objects is moving unless there is a 'background'. Here, former Nasa astronaut Bruce McCandless II is seen floating above Earth using a special personal propulsion system in 1984