Transcript:

So there's a difference between dark matter and dark energy, and I've heard people use it interchangeably, and it's not right. But let's look at dark matter first. The problem is in the word "dark." Here's the difference.

There's a difference between dark and transparent. What's the difference? If light is coming from behind the object and if the object is dark, none of the light reaches the receiver, so the object appears dark — you can see it. If the light goes through the object, it is transparent, and if it is perfectly transparent, you cannot even see the presence of that object because of light.

That is what's happening in dark matter. Light is going through it so perfectly that it should normally be called transparent matter. Why is it called matter anyway? Because it exerts a gravitational force on objects around it and behaves exactly as matter would behave, except it does not interact with light.

Normally, it should be called transparent matter and not dark matter.