"Well I must say even for someone like me, that does sound intriguing." William added as he sat down opposite Thomas, handing the nervous man a drink, before sitting back and taking a sip of the golden brown liquid himself.

Thomas meanwhile, didn't sit back. His elbows were on his knees, his free hand was frantically fumbling around with his chin in an attempt to calm his thoughts. After a short while however he gulped down a mouthful for the same reason.

"So..." William coaxed with a smile on his face. "Are you going to tell me?"

After taking another gulp Thomas locked eyes with William and composed himself.

"Because of the complex nature of this topic, and since I don't know how much you know about astrophysics or even science in general, I feel it's logical to start from the beginning and work my way up, so that you can follow along."

"That makes sense." William agreed. Again with that warm smile that seemed to calm even the most distressed of souls.

"Ok so." Thomas began. "Despite your lack of interest in science, even you will know, the world we live on, all the animals and plants, all the stars in the sky and indeed everything in the known universe is made up of matter. Plain old ordinary matter that forms the building blocks of everything."

"Well I'm glad you have finally realised that fact old friend! I'm glad that brings you such happiness!" William chuckled, pleased with his little joke.

Thomas didn't react, this was no time for jokes. He continued as if nothing had happened.

"Well, alongside this "normal" matter, and I use the term "normal" because it comes down to perspective, there is also Anti-matter."

A spark of recognition ignited in Williams mind.

"Yes, yes I remember you talking about this before! Atoms that have different properties than normal...they have a different electric charge or something around that area? In the same way two ends of a magnet have different charges?" William queried, taking another sip from his glass. Thomas meanwhile was quite surprised William had recalled anything about his last lecture, he had always assumed that his friend forgot almost everything the moment Thomas left the room. So this unexpected amount of retention did come as a pleasant surprise. It was nice to be on at least a similar page as his best friend, it made a change from the normal difficulties they had faced throughout their time together.

As children Thomas would spend his days reading scientific journals until he found something that intrigued him. He would then enthuse to William endlessly about the latest theory or most recent findings. Explaining both how and why those finding were made. Meanwhile William was more bothered about his new shoes or fancy new watch, not really listening to Thomas rant on.

This caused some tension between them initially, as Thomas would get frustrated with Williams lax attitude. The workings of the universe being, from his perspective, much more important than the logo that was printed on your top. Eventually however, Thomas began to accept his friend's different outlook, deciding it was better to have a slightly disconnected friend then none at all.

So this recollection came as a bit of a shock, and Thomas was quite proud of him. He just hoped to high heaven that William remembered what he was going to tell him next.

"Yes along those lines, Anti-matter has the exact opposite charge to normal matter but the same mass; a sort of mirror image of each other. A hydrogen atom that is made up of one neutron, one electron and one proton, will have the same atomic weight of an anti-matter hydrogen atom that is made up of the anti-matter equivalents. Protons have a positive charge and electrons have a negative charge, the anti-matter copies have the corresponding opposites."

"Yes, just like the magnet example I used." William proudly assured himself.

Thomas nodded in agreement, he couldn't be bothered to explain how a magnet's north and south pole was due to the atomic structure of the magnet as a whole, and not the sub-atomic particles at each end being fundamentally different, but Williams's level of understanding would do for now so he continued with his explanation.

"Anti-matter however is an incredibly rare thing in the natural universe. You would struggle to find it outside of a controlled laboratory. This is because if a piece of "normal matter" comes into contact with a piece of anti-matter, the two will completely annihilate each other destroying themselves in the process." Thomas explained.

However he could quickly tell that William didn't quite understand that last part, his facial expression gave it away.

"In other words they both go boom." Thomas reiterated.

William nodded in understanding. "And this discovery of yours involves this anti-matter does it? You have found some in the wild as it were."

Thomas shook his head violently "Not at all, this is just laying the ground work for you, so that you understand that there can be completely different forms of matter. Forms, that if left alone, would react in exactly the same way as our matter does."

William took yet another sip, emptying the glass. "So you're telling me that there is another form of matter, different from our own, but not this anti-matter stuff?" he queried.

This time Thomas nodded, excited to get to the main point of his visit.

"Indeed there is, a form that is relatively new to science. A completely separate form of matter that until very recently, nobody had any idea existed. Something that changes how we look at the universe, and what's especially brilliant, is that this new matter isn't a rare thing like anti-matter, it's far more abundant, and can be found everywhere in nature."

William rubbed his chin, he did it every time Thomas explained something new to him.

"So how come it's taken this long to find it? Surely if it's so abundant, and we can find it everywhere, then we would have found it before now? We can't be looking very hard can we if we have missed it this whole time." William challenged, a good point that Thomas had hoped he would raise.

"That's the brilliant thing, this "Dark", or "Invisible" matter as people have taken to call it, doesn't interact with normal matter in almost any way. We can't see it, we can't feel it, and it doesn't emit or reflect light or any electromagnetic waves. According to our senses it doesn't exist."

William sat up a bit, looking down at his left hand as if he was holding a piece of this ghostly substance. His right hand continuing to rub his chin. After a slight pause he continued with his line of inquiry.

"So how do you know it even exists at all? I'm not being funny but if you can't see it and you can't measure anything from it, surely there's nothing there?"

"At a glance I agree with you." Thomas replied. "It would seem to an educated observer that there isn't anything there, that it's just empty space. But that's only because you're not looking for the right signs. There is evidence for this matter existing, and plenty of it. However it's just not down here on the ground. It's up there among the stars." Thomas gestured up to the sky with his hand, keeping his eyes locked onto Williams, curious to see how his friend would react. "This invisible matter, interacts with our normal matter in only one way. It interacts with us on a larger scale, through gravity. We can see these effects if we just look for the right signs."

"Like what?" William asked? Seeming to be following along nicely, an unusual pattern for him. Normally by now Thomas would have had to repeat himself multiple times to get the point across. Before arriving, Thomas had been mentally preparing himself for the broken record style of explanation he would have to employ. So this level of attention from William was a very welcome surprise. Maybe the offbeat conditions of Thomas's arrival made him realise this was something worth listening to.

"Well to start with, there just isn't enough normal matter to account for the size and complexities of galaxies. Mathematically anyway, there just isn't enough matter to create the gravitational field necessary to hold galaxies together; they should in theory just break apart, sending all the stars within them drifting out into the depths of space in no particular structure or order, but they don't.

Now I admit there are some theories about extremely large black holes at the centre of galaxies acting as a sort of gravity anchor. Holding everything in one place, stopping stars from just being randomly scattered. However that theory still doesn't explain the structures of galaxies we see. Their shapes just don't fit mathematically with this idea. There just needs to be more mass. There needs to be more stuff. Something else must be there to hold galaxies together, to give them the necessary building blocks. Something that we can't see."

Thomas paused, thinking it better to not to overload his poor friends mind. William meanwhile continued his insistent chin rubbing. After a few seconds to contemplate Thomas continued.

"As well as this, light also seems to do strange things that can only be explained by the presence of...something. Light coming from distant sources seems to bend around seemingly empty areas of space, as if planets, stars and indeed whole galaxies were there. But when we look with our telescopes we find...nothing. Again this can only really be explained by actually having something there. There are areas of space completely devoid of stars or galaxies and yet we see this light bending effect."

"What about black holes, like you mentioned?" William said in a smug manner. "We can't see black holes. You're probably just looking at a lot of them all bunched together."

Thomas was quick to burst his friends bubble. "Not so, black holes violently effect everything around them whereas this "Dark" matter seems to be scattered everywhere. The light bending effect can be seen very close to neighbouring stars without the stars themselves being effected."

William put his glass down on the table, "So everyone only suspects that there is something else out there, floating around? Holding the galaxies together as you say. But it can't be proven 100%?"

"Yes, its only been an educated guess...up until very recently!" Thomas beamed with a big smile on his face. "The existence of this mysterious matter had only been suspected due to these signs. Since you can't actually see anything, there isn't any concrete proof that something is 100% there. Anomalies with equipment or a combination of normal matter in a complex way can create some of these apparent "Dark" matter signs." He explained.

"However I can now confirm the existence of this incredible substance with 100% certainty." Thomas began to shake with excitement. "That's why I came here Bill! I've invented a device that lets us see it!"