Everyone on the DART is attracted to you
gravitationally...

We all know that gravity is the reason why things fall to the ground when you drop them. It’s why when you jump, you don’t just float away. The reason why objects are attracted to the Earth is because of its mass. The Earth has a lot of mass, and the more mass something has, the more gravitational force it exerts.

All objects that have mass are gravitationally attracted to each other

That means phones, coins, trains and yes, even you are all exerting a gravitational force. It's just that the extremely massive Earth has far more 'gravitational pull' than any of these other objects. That’s why when something falls, it falls towards the Earth.

Click and hold here

Even though there are still some mysteries around gravity that are unsolved...

Understanding how it works has helped us to do some pretty incredible things. Even though no one had 'discovered' it, the existence of Neptune was predicted through observing irregularities in the orbit of Uranus – irregularities that would only make sense if another planet was exerting a gravitational pull. Once the prediction was made, astronomers searched the sky to confirm that the new planet was indeed there.

From planets that are there, to mass that isn't...

Observation of gravitational forces led us to realise the the universe is missing lots and lots of mass. We call this missing mass Dark Matter, because we can't see it and we don’t really know what it is yet. Astrophysicists are working to understand how we might detect Dark Matter, which is estimated to make up a massive proportion of the total matter in the universe.

Gravity affects everything around us

and it seems like a powerful force. But actually, it’s not. Think about it: we’ve evolved to escape gravity, if only briefly, by jumping. Of the four fundamental forces, gravity is the weakest. In fact, it’s a billion, billion times weaker than the forces that bind atoms together.

The Four Fundamental Forces

The current thinking in particle physics...

is that the four fundamental forces all exist in nature as fields. When one particle exerts a force on another physically, a third particle is required to 'mediate' that force, or carry the energy from the field between the two particles. For example, the electromagnetic field is mediated by the photon, which you may know as the quantum of light. For gravity, the graviton has been theorised but not yet detected.

Gravity was first described by Newton in 1687

but there's still lots about gravity that we don't know. For instance, we don't know which particle mediates gravity. We've named it the graviton and there's teams around the world trying to find it based on theories of how we think it works. But we don’t know for sure.

Newton's apple is one of the most famous science stories ever.

Many have dismissed it at a myth but actually, not only did Newton himself often tell the story, some of his contemporaries agreed that the flash of inspiration for his work on gravity came to Newton after seeing an apple fall from a tree. However, the apple didn't – as the story often goes – fall on top of his head.

So, it’s true, everyone on the train is attracted to you

Because you have mass. And since everyone else on the train also has mass, you’re attracted to them too – gravitationally, at least.