Hip-hop and science collided this week thanks to a surprising theory revealed by B.o.B. If you let the rapper tell it, the earth is flat. He's not the first guy to believe such a thing, but his words reignited a centuries-old argument. "A lot of people are turned off by the phrase 'flat earth' ... but there's no way u can see all the evidence and not know... grow up," he wrote on Twitter Sunday (Jan. 24).

As a result of his belief, which he supported on social media through images and personal findings, astrophysicist Neil deGrasse Tyson came flying in donning his scientific cape and engaged in an entertaining conversation on social media about the shape of the earth. According to Tyson, the Psycadelik Thoughtz creator is making a big mistake with his theories. Centuries of scientific facts stop B.o.B even before he got started with his flat-earth conjecture.

A look through both of their Twitter timelines prove they're passionate about earth's shape. So passionate that they each created diss tracks to get their points across. On B.o.B's haunting "Flatline," he affirms his theory by calling out those that try to keep him silent. “Globalists see me as a threat, free thinking got the world at my neck,” he raps. “Neil Tyson need to loosen his vest, they probably write that man on hell of check.”

As for the 57-year-old astrophysicist, he called on his nephew Stephen Tyson Jr., who also raps, to do the lyrical dirty work and craft a diss track, "Flat to Fact." "I’m bringing facts, took a bat at silly theory / Because B.o.B has got to know that the planet is a sphere, G,” Tyson Jr. rhymes over the instrumental to Drake's "Back to Back." Self-proclaimed nerds and rap heads alike can get into this war of words.

While the lyrics on both sides are entertaining (and a bit hilarious), the director of the Hayden Planetarium at the Rose Center for Earth and Space in New York City doesn't find anything funny about the 27-year-old rapper's claims, which reached his more than 2.3 million followers on Twitter. Tyson has a comical side himself, but when it comes to the earth's shape, he's ready and willing to provide the facts. After a hectic week of being thrown into the world of hip-hop, XXL got on the phone with Neil deGrasse Tyson to hear his side of the earth beef with B.o.B.

Read on to find out what Tyson really thinks of B.o.B's theory, how the "Flat to Fact" diss track was created and his own history with hip-hop.

XXL: How did it first get on your radar that B.o.B was tweeting that he believes the earth is flat?

Neil deGrasse Tyson: That’s a great question. Generally in the morning I’m minding my own business and just hoping that I can just get some work done. My Twitter stream lit up with people saying, "Look at what this guy‘s posting. You gotta tell him he’s wrong." So I say, "Who are these people?" Well, they’re all followers of B.o.B. And not to over-read their sentiment, but my feeling was they were coming to me to say, "Can you save him from himself? You cant let this go unchallenged."

I heard of B.o.B. I’m not into him 'cause they’re so many great musicians out there. And so I looked him up and reminded myself of some of his more popular ones that hit a couple years ago. And then I said, "Holy shit! He‘s got 2.3 million Twitter followers so all this flat earth stuff is going to a boatload of people." If this didn’t come across my threshold I would’ve just said let it be. This is the internet, it’s a free country, you can think what you want. And then I looked at what he was saying on his tweets. He was saying I’m applying physics and math to solve this and here’s why the earth is flat. And I said, "Oh, now you crossed a line there, buddy."

If you’re gonna say you’re invoking physics and math rather than just saying it looks flat to me therefore I think it’s flat, if you’re gonna say I calculated this and it shouldn’t be the case… And then I said alright he’s using the laws of physics in defense of something that’s just completely false. So I addressed two of his tweets. He had many, I lost count. One of them in reference to the New York City skyline, thinking it would be behind the curvature of the earth without remembering how tall the buildings are. And he asserted that you could see the North Star from the Southern Hemisphere. But of course you can’t. So I accused him of never going to the Southern Hemisphere or if he did, having never looked up.

I try to be playful but informative. I’m still an educator at heart. So that was it. I didn’t know how to react to this fact. People said, "Well, do you want to debate him?" No, no. The real issue is what is going on in the education system that we can have adults come out the other side thinking the flat earth is the right way to go. What is missing? I’m an educator and these are the kinds of questions I pose.

So rather than debate people who don’t know how to process information and arrive at an accurate conclusion about the world, I would think how can we fix the curriculum or how can we trigger a sense of curiosity in the world where people look to find answers to questions rather than cherry pick falsehoods to defend what they want to be true anyway. That’s really what conspiracy theorists do, for example. Because by the way if you are certain the world is flat, then the photos of the round Earth from the moon, you have to be in denial of those. And therefore you have to say the moon is faked. It’s a rabbit hole that you go down, typically. And so it’s not what I normally do. I normally just put tweets that enlighten people and you make your own conclusions.

So in your scientific terms, why is it not possible for the earth to be flat?

It’s possible, it’s just not. Anything can be any shape. I think what you can ask is if it were flat, what would you notice? If it were flat , you’d see a ship forever as it sailed away from you. But the ship disappears over the horizon. These were early tests of this. During a lunar eclipse, earth’s shadow… as the moon enters earth’s shadow, and the shadow is always curved. And the only shape that always leaves a curved shadow is a sphere. A perfectly curved shadow.

So you can get it from lunar eclipses, you get it from photos from space exploration especially from trips to the moon, you get it from traveling in an airplane where you realize that we all actually need different time zones to accommodate. Time zones only have meaning in a spherical earth because the angle of the sun is different for everybody as you go around the curve. If we were all flat, then the angel of the sun to earth would be the same for everybody. It would be the same time everywhere. It would be noon at the same time for everybody. Things like that, there’s no end of these kinds of points that one can make. If you’re armed with accurate mathematics rather than whatever mathematics B.o.B was using, then you can show what should be visible over the horizon and what wouldn’t be and you wouldn’t be making the mistakes he did.

One of the questions B.o.B asked you directly on Twitter was “Why can’t the curvature of the earth be measured anywhere in nature?” Can you answer that question?

Yeah, we measure when we go to the moon and you can see the curved Earth, unless the moon is not in nature [laughs]. What I said [Wednesday] night on [The Nightly Show with] Larry Wilmore, is we know from mathematics, and we know it empirically, but we also know from mathematics, that if you can be sufficiently small on a curved surface so that that curved surface will look flat to you, as human beings on a ball that’s 8,000 miles in diameter counts as being too small to notice just by walking around. So you need some other tools to establish this. By the way, it’s nothing wrong by thinking it by saying, “It looks that way.” We went through centuries, millennia, of people thinking the earth was flat. The very word Mediterranean means “middle earth,” where you had the early civilizations. These are people thinking they are in the center of flat earth. If you knew it was a sphere, there’s no way you can think of yourself as the middle of anything on its sphere. The surfaces of spheres have no middle -- an interesting fact of geometry there.

You’re too small to measure it on your own so you need clever devices and you need transportation and you need ways of ascending to have a much higher view than just crawling around like an ant on a huge ball. So right, you can't demonstrate it if you’re just walking around. Otherwise it wouldn’t have been so late in the history of civilization where it was discovered that it wasn’t. So this is why I say in my final tweet [to B.o.B], “Duude — to be clear: Being five centuries regressed in your reasoning doesn’t mean we all can’t still like your music,” and so he’s thinking the way people thought five centuries ago. But we’ve developed methods and tools that improve our ability to decode what is true and what is not in the world and the universe. This is what’s called science.

When you first heard B.o.B’s “Flatline,” his diss directed toward you, how did you react?

He’s an artist so I don’t critique the art of artists. So that diss track, it was a diss track. It was fun. I liked how he said ”pop the button on your vest.” Some line about my vest. I’m flattered I could be the subject of a song even if it’s a diss track. In the end I think the public was entertained watching this exchange.

Why did you decide to do the “Flat to Fact” diss track after B.o.B dropped “Flatline”?

The rebuttal diss track. So my nephew [Stephen Tyson Jr.] is actually in graduate school studying how hip-hop culture can make positive change in neighborhoods. He also raps on the side. He’s my rap consultant because I’m an astrophysicist. Maybe he’s glad occasionally he has an astrophysicist to reach to. So now I’m calling him up. If like there’s a comet discovered so of course he calls me up to get the explanation. Now the tables are turned. So B.o.B called me out, this is what happened. He said, “Do you realize he did a diss track?” I said, “No.” He sent me the link and I listened to it and I said, “You gotta do a diss track back!”

I said that, he might have already been thinking it but that was my first thought, which is very juvenile, schoolyard. But it was a fun, first thought. He said, “Yeah, I can do it.” So I said, “Can you do it like this morning?” He said, “I don’t know but I’ll try.” So that morning he finished the diss track by like one in the afternoon. My final tweet once the diss track was ready was “I’m an astrophysicist not a rapper but I know rappers and this one has my back” and then I gave that link [to “Flat to Fact”]. [Tyson] composed it that morning. [Stephen] wrote it, he composed it, recorded it that morning. I said we can’t waste time on this. I need something now. And I think he sampled some people’s music for the background.

Yes, he used Drake’s “Back to Back” instrumental. That was used in his beef with Meek Mill.

Yeah, so this is deeply, culturally connected, this whole sequence it turns out. I was pleased to be able to specifically and directly fight fire with fire and water and water. You dissed me, I need a diss track [laughs]. It’s so playfully juvenile. I just want to go back to my life. I don’t do this.

For your nephew do you think this will help his rap career in some way?

Well, I told him, “Can we get a rebuttal to this?” He said, “Yeah I can do it.” And I said, “Will it be good? If this shit’s not good I’m not posting it.” So he was on notice that morning and under pressure. And then when he finally sent it to me and I listened to it I said this’ll work. He was ready. If it can serve the needs of this greater good, then it serves the needs. Perhaps it’s true that for a lot of artists they need the break, they need a moment where they can have exposure that wouldn’t otherwise come. It’s unfortunate but true, right, that if you just simply have talent it doesn’t always rise to the top. Somebody has to notice you. I get it. I would rather it another way. By the way, with the internet, it lowers the threshold of people’s access to you. So if you are really good, people can know and you don’t have to go through record deals and everything and convince people.

You also said in the "Flat to Fact" diss that “Flat earth is a problem only when people in charge think that way.” Can you address that?

Sure, so in a free country, think what you want, believe what you want. I don’t have any problems with that. That’s kind of what it means to be free. If you are forced to think or believe things by some authority that’s not a free democracy. We have words for that, they’re like dictatorships. We have words for societies that fall into those categories. So I don’t care. But in a pluralistic society where people believe different things and have different views and they have different religions, if you are going to be in charge of legislation that has to affect everyone, it seems to me you should base that legislation on things that are objectively true. And these are things that are brought to you by the methods and tools of science. And then after that, debate it how you want once you establish the objective truths. You can live in your flat earth colony, no one is gonna stop you. If you’re in charge it means you’re making decisions that affect others and if you’re basing those decisions on falsehoods or misconceptions or anything that is not connected to reality, that is dangerous for the health, the wealth and the security of the nation.

So would you say B.o.B believing that the Earth is flat, that’s a dangerous thought to have?

Well, dangerous is a very strong word. I would rather caste it slightly differently and say innovations in science and technology are the engines of this century’s economy. And they are the foundations of our health, our longevity, our security and like I said our wealth. If you are going to breed a generation of people by whatever influence you have power over to not understand what science is and how and why it works, you are undermining our ability to stimulate our health and our wealth and our security. You’re undermining our ability to maintain that or to grow it or improve it. So that would come the dangers, especially with regard to your security or with your health. Your wealth, you can be poor or rich, who cares but your health or your security you probably care about that. I don’t want to say danger. I’m not calling him dangerous. I’m saying it would be unfortunate if his influence spread far and wide. It would be unfortunate for the future of those three categories of what we value so much in this society.

Tell me one word to describe how you felt when you saw B.o.B’s tweet that he believed the earth was flat.

It wasn’t so much one word it was more like, “Oh, I hope this amounts to nothing,” because I didn’t really want to engage this. But it did and it amounted to something a lot.

Do you have any final thoughts to say to B.o.B?

Not beyond my final tweets or the bit [Wednesday] night on Larry Wilmore. In other words, when I have something to say and I want the public to know it I will post it. Beyond that, I don’t retain thoughts that I might post but don't. Your question might normally have an answer but for me, it’s already been answered and what is already publicly posted.

Are you a hip-hop fan at all?

I wouldn’t say that I’m an aficionado. But when a good tune comes up, I know it and I feel it. I tend to be a populist if I can say that. The tunes that really make it big I find myself highly attracted to those tunes. I couldn’t have some nuanced conversation with you about the up-and-coming rappers and where they’re taking their craft. I enjoy watching the dialogue regarding Iggy Azalea being from Australia and the culture, the politics surrounding that. I’m an outside observer looking over the fence. That’s how I would said it. And looking over the fence is because I’m culturally curious not so much “Oh, I want to be a rap star myself.” No, it’s just I’m culturally curious. Anything really important my nephew tells me about it anyway.

Is there a rapper that has ever caught your interest, even when you were younger?

I remember, I was alive and partying in college when “Rapper’s Delight” came out, when Kurtis Blow’s “The Breaks.” You know, two of the earliest charting genres. Frankly, when I heard those songs we partied our ass off to those songs. If you had asked me at the time in 10 years or 20 years out what would still be here, rap or disco, which was also peaking at around that time, I’d say of course disco. This rap, that’s just a flash in the pan. It’s kind of a novel thing and its fun. And holy shit. Hip-hop is a whole freaking industry and disco is long gone. Yes, there’s some spirit of it in some songs in the Hot 100 but no one is saying “It’s disco music,” it’s just dance music. In terms of a cultural force, I was completely surprised by [hip-hop]. And delightfully surprised. I’m from the Bronx, which I think claims some of the roots, the deepest roots of hip-hop.

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