“Meg, do we really need to have that on?”

The pegasus shuffled her wings in annoyance as she tossed her brother an annoyed glance before returning her eyes to CNN. “It’ll start any minute,” she said. The sound was off, in concession to Matt, but a pair of lecterns adorned with the presidential seal filled the screen. On either side were the flags of the United States and the Griffon Empire. It was to be held in the White House Rose Garden.

Lori came to her defense. “You have to be a little bit curious,” she told her husband, “about what they’ll say.”

“Not that curious,” he grumbled. “It’s not as if it won’t be repeated endlessly for days.”

Tiny hooves, accompanied by shouting, scampered across the ceiling.

“I’ll take care of that,” Rarity said. She got up, startling her cat, and daintily lowered herself to the hardwood floor.

Opalescence hissed in annoyance.

“Behave yourself. We are guests in this home.” The unicorn addressed her hosts. “I’m terribly sorry about that, but I assure you she’ll behave herself.”

More scampering of hooves.

She sighed dramatically. “And so will Sweetie Belle and her friends.” She glanced at the TV. “I do hope they don’t start before I return.”

“We’ll pause it if they do,” Lori said.

“It’s quite amazing you can do that.” Rarity headed for the stairs.

Meg waited for her to get out of earshot before saying anything. “I sometimes wonder who’s in greater denial: Rarity about Opalescence or Fluttershy about Angel Bunny.”

The cat in question made a point of ignoring them, occupying herself with licking a paw.

“We agreed to having the Crusaders visit Susie,” Matt said. He sullenly considered the cat. “Not run an experiment.”

“It’s just a cat,” Meg stated, as if that rationalized everything.

And Opalescence was just a cat. Her DNA had been checked. There was nothing to distinguish it from earthly cats. The same was true of Angel Bunny; he was genetically indistinguishable from earthly rabbits. So how were they so—for lack of a better word—intelligent?

The obvious answer was magic. So what happened when they were put into a magic-less environment? Did magic allow them to form better brains, or did magic let those brains function better? Or maybe some of both?

At least it didn’t involve time loops and a message from the future. Discord hadn’t seen fit to make himself available anyway. And was there really any urgency?

Matt shook his head. “At least she’s not a certain rabbit.”

Meg couldn’t agree more. And as somepony was needed to keep the CMC on a short leash, and Rarity was a logical choice, and she was available, and she had a suitable pet…

“Why aren’t you using your new pendant?” Lori suddenly asked. “I get it, that you have to be a pony to bring others with you to our house, but do you have to remain a pony now that you’re here?”

Meg touched her pendant with a hoof. This time it hadn’t stop her transformation to a human; swallowing the plaid pill did that. “Actually, I do. That kind of magic doesn’t work in our universe.” She glanced at the TV. There was a panel discussing whatever, while the waiting lecterns occupied a corner of the screen.

Opalescence yawned, then threw an accusatory look at Meg.

“What?” she rhetorically asked. Magic or no magic, it certainly didn’t affect that cat’s behavior. But was the lack of magic making her less intelligent?

The cat resumed licking a paw.

Quite honestly, a cat may not have been the best choice. As much as she hated to admit it, Angel would have been a better subject. Hell, Tank would have been a better subject.

The sounds of soft hoof clops returned. As before, Rarity used telekinesis to gracefully assist herself up onto the sofa. Opalescence deigned to return to the unicorn’s side. “Miss me?” she cooed. As compensation she petted her, which the cat dutifully tolerated.

One thing was certain: Opalescence gave no indication that she noticed entering or leaving Rarity’s magic bubble. But would the cat notice a change in her own intelligence, if such a change was in fact happening?

The lectern and flags filled the entire screen. Two persons were carrying a sizable box made of wood over to the lectern nearest the griffon flag. “Maybe it’s about to start?” Lori asked. She unmuted the TV.

“—just the right size to elevate the griffon ambassador to the microphone.”

“Shouldn’t it have been in place before now?”

“Maybe they just finished nailing it together? It’s not like they’d have something like this lying around.”

“It still shows a lack of planning—”

Lori muted the TV and looked towards Meg. “Any inside info about that?”

“Not in the loop on this one. All I know is that Twilight brought the Ambassador and a few other griffons to the White House yesterday, left them some magic generators, then quickly departed. This doesn’t involve ponies, and the griffons want it that way.”

“No plaid pills?” Matt asked.

“I’m afraid not, darling. That’s still on a need-to-know basis; and besides, those pills wouldn’t last even a full day, never mind two.”

Matt looked confused. “So… they switch over to magic generators when their magic runs out?”

“It doesn’t work that way,” Meg said. “The failsafe kicks in, and you return to Equestria.”

“Really? How come you’ve never mentioned that before?”

“I had no reason to? I mean, I’ve never experienced the failsafe myself.”

“Nor I.” Rarity tilted her head in thought. “Though I do believe Rainbow Dash once did.”

“She did?” Lori asked. “How’d she manage that?”

Meg rolled her eyes. “By chasing a commercial jet as it headed out over the ocean. She ran out of magic long before it reached cruising altitude.”

“She can fly that fast?” Matt asked incredulously.

“I’m sure the plane was nowhere near cruising speed, but yeah I believe it. No idea what her top speed is, or whether it’s the same here as in Equestria. Maybe we should properly measure it someday.”

Rarity gave a smile that definitely was not a smirk. “You wouldn’t have to ask her twice.”

“I bet,” Meg said, “and with a nuclear-powered magic generator, she won’t have any problem hitting her top speed.” Her head tilted in thought. “Pretty sure a sonic rainboom is still not an option, though, not in our universe.”

“A nuclear-powered Rainbow Dash,” Matt muttered. “Just what the world needs.”

Lori shushed him as she unmuted the TV again. President Serrell and Ambassador Gosswell had emerged from the White House and were walking to their lecterns. Upon reaching them, Gosswell briefly flapped his wings to get on top of the wooden box. They briefly posed for photographs.

“I wonder if there’re any pony or griffon reporters present,” Lori mused.

“Pretty sure there aren’t any,” Meg said. “Some day, I suppose. It’s only a matter of time.”

President Serrell adjusted his microphone. “With all the attention on ponies recently,” he began, “it is important to remember that Equestria is not the only nation in our sibling universe. These past two days with Ambassador Gosswell have been quite productive. I’m pleased to announce that we have started down the long road to establishing formal relations with the Griffon Empire.”

He looked to the ambassador.

“Unfortunately, it will indeed be a long road,” the griffon said. “Not due to lack of interest on either side, but simply because travel between our worlds is so limited—doubly so for us, as the means of such travel are exclusively in the possession of Equestria.

“However…” The griffon swung a talon back to the building. “As a token of goodwill, I offer this gift to your great nation.”

The doors opened and another griffon emerged, pushing a dolly. On it was a sizable cage, and in that cage was a strange bird—quite a large bird too, standing about three feet tall. Its wings seemed too small; did it use flight magic? Its beak was long and bulbous. Quite honestly, it wasn’t a terribly attractive looking bird. Just as well the camera didn’t or couldn’t zoom in on it.

The caged bird was rolled between the two lecterns. It seemed utterly unconcerned about its situation, just mindlessly standing there, idly surveying its surroundings. The griffon who had delivered it returned inside.

“I present the dodo, a bird which—though extinct in this world—lives on in a territory of our empire.”

Dozens of photos were snapped, to the complete disinterest of the bird.

“How do we even know that’s really a dodo?” Matt asked.

“DNA testing?” Meg said. “I’m sure there’re suitable fossils in some museum somewhere. It’s not like it went extinct millions of years ago.”

“Sure acts like the proverbial dodo,” Lori said.

Serrell had been making a show of inspecting the bird, accompanied by the sounds of camera shutters. Meg found it unlikely this was the first time he’d seen it. The griffons must’ve brought it with them, which meant… “I wonder how they knew it had gone extinct here?”

“I believe Twilight told them,” Rarity said, “and suggested this gesture of goodwill. I, myself, had no idea that the dodo existed in either realm.”

The bookhorse had clearly been putting her internet connection to good use.

The President returned to his lectern. “We shall treasure this bird, Ambassador. One day, it may be possible to repopulate the islands where the dodo once thrived.” He faced the cameras. “Of course, the dodo isn’t the only species to have suffered extinction at the hands of humanity. Who knows how many others still exist in that other world?

“We’ll take a few questions.”

That was unusually short for a joint speech, Meg thought. Did they really have that little to say in public?

“Any wagers on how long before they ask Gosswell about the cartoon?” Matt asked, to disapproving faces. “You know they all saw 60 Minutes.”

The first question was asked: “This is for the Ambassador. How did you know about the extinction of the dodo in our world?”

“From Princess Twilight Sparkle, believe it or not. She thought it would help us make a good first impression, and I saw no reason to disagree. As to how she knew, you’d have to ask her.”

Rarity smiled, but said nothing.

“Also for the Ambassador. Would you be open to establishing relations with other nations, in addition to the United States?”

“Without question. The Griffon Empire has diplomatic relations with all the nations of our realm, and we would be open to diplomatic relations with all the nations in this one.” He paused for a second. “Though they would have to first admit we actually exist,” he deadpanned. He turned to address Serrell. “Hard to believe that’s still a problem.”

The President shrugged in response. “I believe you exist.”

A few too many seconds went by before the next question was asked.

“This question is for either of you. It had been mentioned that there were ’challenges’ that had to be overcome before proper relations could be established. Is the fact that the Ambassador is here evidence that they’ve been overcome?”

“That’s a clever way to phrase it,” Lori muttered.

“Indeed,” Rarity added.

“Partially,” the President finally said. “I’ll let the Ambassador speak for himself.”

There was the smallest crack in Gosswell’s demeanor. “The My Little Pony cartoon,” he said, getting those words out of the way. “It’s hard to believe such a thing is possible, but I’ve now seen it with my own eyes.”

He took a breath. “We believe that the Equestrians are taking the right approach in regards to that cartoon, and we shall be following their lead. They are far more impacted by it than us, after all. As for that Griffonstone episode…” The Ambassador rolled his eyes. “As offensively as it depicts griffon society, it is so ludicrously wrong that it lacks the power to outrage.”

Serrell held up his hand. “That’s all the time we have for questions.”

He and the Ambassador turned around and returned to the White House. A staffer pushed the dolly towards the journalists and away from the lecterns. “Please form a line to see the dodo,” he said. The bird cocked its head, unfazed by the latest developments.

An off-camera Anderson Cooper was giving a summary of what had just happened.

“That seemed to go well enough,” Rarity observed.

Meg had her doubts. “Don’t judge until the talking heads put their spin on it.”

“Do you really think the griffons will look at the Griffonstone episode that way, or was the Ambassador just saying that?” Lori asked.

“I honestly don’t know,” Rarity said. “I’m sure they’ll try to spin it that way. But if they’re truly following our lead, then the average griffon will no more know of that cartoon than the average pony—which is to say, not at all—for quite some time.”

“How do you feel about being in those cartoons?”

The unicorn gave her cat a smile. “I feel that it is not productive to dwell on that question.”

The video had switched to the CNN studio, with Anderson Cooper presiding over four seated commentators. “Any first impressions about what we just witnessed?” he asked.

“Well, the first question that must be asked is, quite simply, is that a real dodo? I mean, what are the odds that a different world would evolve an exact duplicate?”

“The dodo went extinct only a few centuries ago,” said the second panelist. “I’m sure a DNA sample could be acquired from a museum. We’ll know soon enough if it’s real.”

“Assume for now that it’s real,” Cooper said. “What then?”

“Then,” said the first panelist, “there’s only one way the griffons could have them. They visited our world centuries ago and helped themselves.”

“That’s ridiculous,” a third said. “They have no means of traveling to our world. Princess Twilight brought them over.”

The first waved that off. “So the ponies helped themselves to some dodos and for some reason they wound up in griffon territory. The point still remains: it simply isn’t credible that the dodo independently evolved on a different world.”

“It’s not just the dodo,” Cooper said. “I was there. I saw forests, farmland, birds… I have no idea if they’re the same species as exist in our world, but I wouldn’t be surprised if they were. Surely the ponies—or whoever—didn’t ‘help themselves’ to a proverbial Noah’s ark in order to populate a barren world.”

“Sounds like that dodo isn’t the only creature from which we should demand a DNA sample.”

A pit formed in Meg’s stomach. That DNA sequencing had happened months ago. How much longer before it all leaked, now that it had entered the public consciousness? Those samples included two from herself, one as a human and one as a pony.

The fourth panelist spoke up. “Then there’s the question of mythological creatures. How do we know about unicorns, pegasi, minotaurs, griffons, dragons, manticores, and the other creatures that exist only in their world?”

“I thought Tirek had made that perfectly clear,” Rarity said.

The first panelist grunted. “I’d love to see DNA samples from those creatures.”

The pit grew larger.

“What impact will this joint appearance have on the ongoing protests against Equestrians?” Cooper asked.

“Which protesters?” the third asked. “The ones convinced this is all a hoax? Or the ones convinced that ponies mean to conquer us?”

“I’d say the latter have new cause to demand impeachment,” the first said. “How can Serrell deal with the Equestrians while these new questions remain unanswered? How did they acquire dodos from our world? What else have they acquired?”

“I’m afraid I must agree,” said the second panelist. “I have little doubt that the Senate Judiciary Committee will reopen its investigation. Senator Routledge will see to that.” He shook his head. “Though I feel we should wait for DNA results before rushing to judgement.”

“Serrell is damned either way. Either DNA proves it’s a genuine dodo, in which case either the griffons or the ponies pilfered them from our world, or it’s not. In that case, they’re passing off a fake as the real thing.”

“Let’s switch subjects,” Cooper said. “An atomic clock had been on loan to the Equestrians for a few weeks, to measure gravitational time dilation on their world. Recently the results were announced. The one in Luna’s observatory, which I saw, ran about seven billionths of a second per day faster than the one down in Ponyville. Any reaction?”

Steve switched on the projector. On a makeshift screen played a washed-out video of a planet orbiting about its star due to the curvature of space-time. “Could somepony turn down the lights?”

A unicorn obliged, without bothering to get up off her cushion. The warped grid of space-time popped into clarity. Steve kept his attention on Arcane Scroll as he resumed his lecture.

“The mass of the central object warps the surrounding space-time. As a result, the orbiting object finds itself going around in circles, even though it’s traveling in the straightest possible line.”

There seemed to be a lot of skepticism—and Steve had gone out of his way to avoid mentioning “stars” and “planets” as it would have only confused matters.

One pony finally spoke up. “So… if you shine a light from that circling object, would the light also go around in a circle and hit the object from the other side?”

“Actually, no. To go around in a complete circle, the object would have to travel at precisely the right velocity. The larger the central mass, or the closer to it, the higher that velocity must be. The speed of light far exceeds that. The path of the light will curve, but only slightly.”

“Could that central mass be so large that even light would circle it?”

Steve smiled. “Yes. We call such objects ‘black holes,’ because their gravity is so strong that not even light can escape—though why light cannot escape is not as straightforward as it may seem.”

Another pony spoke up. “How can you say that the circling object is traveling in the straightest possible line when you just admitted that light would travel an even straighter line?”

“If we were talking about curved space, and not curved space-time, you would be right. Remember that all objects travel through space-time at the speed of light; what appear to be different velocities are actually different directions. This affects how the curvature is experienced.”

Arcane Scroll finally spoke up. “That… movie doesn’t make any sense. Yes, if you drop a heavy object onto a rubber sheet, it’ll form a depression as depicted, and a small ball traveling at the right velocity will circle the inside of that depression. But those things happen only because of gravity.” The professor fixed his eyes on the human. “Your explanation of how gravity works requires gravity to work.”

Steve leaned over his computer and stopped the playback. “You’re absolutely right, of course. It’s a terrible metaphor, but unfortunately it’s the best visual metaphor we have.”

That admission seemed to please the professor. “Then let’s dispense with it. I lift an object, then I drop it. It falls, picking up speed. Why?”

Steve spent a few seconds to come up with an explanation that didn’t require tensors. “Imagine we’re in empty space, where space-time is perfectly flat. We populate it with a collection of objects that, for now, do not warp space-time with their mass. They are at rest with respect to each other, all traveling in the same direction: the future. Their paths form parallel lines that will never meet.

“But objects do have mass, and they do warp space-time. They impose upon the surrounding space-time a positive curvature, like the surface of a sphere. If you try to draw parallel lines on a sphere, you’d find that they’ll eventually meet. That’s a property of positive curvature: parallel lines meet.

“In the case of a gravitational field, that curvature causes the paths of objects to deviate, away from the future and towards the center of their collective center of mass. We perceive that as the objects falling. This deviation causes a rotation of the objects’ frame of reference relative to an observer far away in empty space. But that’s how velocity is represented in space-time: as a rotation of one frame of reference with respect to another. The objects pick up speed as they fall.

“Now, the curvature of the space-time we’re in—right here, right now—is very slight. No measuring device is going to pick up the deviation from perfectly flat geometry. The reason that slight curvature is sufficient to produce the gravity we observe is because we’re following that curvature at the speed of light.

“But only when we are in free-fall do we travel through space-time in straight lines—at least, the straightest possible given the curvature. None of us in this room are in free-fall; the floor prevents us from falling. That floor is pushing back, accelerating us just enough to cancel out the change in velocity caused by the local space-time curvature. Ironically, even though we’re not apparently moving, our space-time paths are bent, deviating from straight lines.

Steve dramatically paused. “And then there’s light. What happens to light when we send it straight up? Any guesses?”

One of the younger mares volunteered an answer. “It slows down?—no, wait, it can’t slow down.”

Steve shook his head. “No. Light can only be observed as traveling at one speed; the space-time interval it traverses between emission and absorption is always exactly zero. Climbing out of a gravity well does not change that. But to a distant observer, light is affected. It shifts color, towards the red end of the spectrum, because red light has less energy than light of other colors.

“It’s easy to conclude that light loses energy as it climbs, just like an object slows down as it climbs. But losing energy is change, and change requires the passage of time, and light does not experience time. If it doesn’t experience the passage of time, then it cannot change; and if it cannot change, it cannot lose energy.

“So why does light that originates in a gravity well appear redder when observed outside that well?”

He scanned his audience. Nopony volunteered an answer.

“We recently conducted an experiment using atomic clocks. One was placed at the highest point in Canterlot, in Princess Luna’s observatory. The other was down below in Ponyville. What’s special about atomic clocks is their incredible precision. They drift by less than a nanosecond per day—that’s a billionth of a second.

“Upon arriving in Ponyville from my realm, the two clocks were synchronized. One then went to the observatory. The two clocks happily ticked away for over a week. Afterwards, the one up here was returned to Ponyville. Once they were again side by side, their times were compared.

“Raise your hoof if you think the clocks were still synchronized, having drifted apart by no more than what their inherent precision would permit.”

No hoof went up.

Steve smiled. “Good. You’re catching on. No, they were not synchronized. As to how much they had drifted apart, let’s go calculate that.”

He wrote the following equation on a blackboard:

\sqrt{1 - \frac{2m}{r}}

“What this equation computes is the amount by which time slows down due to gravity. It’s surprisingly simple. All you need to know is the mass of the object generating the gravity and the distance from its center.

“Now I know what you’re about to say: you can’t divide mass by distance. And that’s ordinarily true. But it turns out there’s a geometric interpretation to mass: it’s the radius at which that mass becomes a black hole, the point at which surface gravity becomes so high that not even light can escape.

“So what numbers do we plug in? Well, for my home world, we use zero point four four four for the mass, and six three seven one zero zero zero zero zero for the radius—that’s putting everything in centimeters. And doing the math, we get about seven-tenths of one-billionth. That is the factor by which time slows down.

“But we can’t measure that directly with just one clock. What we can do is to put two clocks at different altitudes and measure the difference in the flow of time due to the difference in heights. The observatory is about twenty-five hundred feet above Ponyville. Plugging in the numbers, we can predict that the Canterlot clock will gain about seven point two nanoseconds every day relative to the Ponyville clock.

“That, of course, assumes that this world has the same mass and size as my world.”

Steve paused, waiting for somepony to ask the obvious question.

“So… is it?”

The question asked, he provided the answer. “The observed gain was seven point one nanoseconds per day, within the margin of error. That implies our worlds are in fact the same size and mass. We can add that to the list of coincidences, I suppose. It also shows that General Relativity applies to this realm.

“Anyway, the reason gravity redshifts light is because it slows down time. If, for example, time runs ten percent slower, then light will have ten percent less energy, and that makes it redder. The observed redshift depends on the observer, of course. Somepony in that same gravity well, her clock also going ten percent slower, will not see any redshifting.”

Somepony raised a hoof.

“Yes,” he said, pointing at the stallion.

“Looking at that equation,” he began. “If the radius was smaller than twice the mass, you’d be taking a square root of a negative number.”

“Ah, yes. That hints at the weirdness of the interior of a black hole.” Steve noticed Princess Luna standing in the back of the hall. “And that will have to be the subject of a future talk. I’m afraid that’s all the time we have for today.” He nodded to the princess.

The attendees looked back and saw Luna walking towards the front of the lecture hall. They quickly got to their hooves and briefly bowed.

“Professor Arcane Scroll, would you stay a moment? The rest of you may depart.”

“Of course, Your Highness.”

“We shall wait until the others have left.”

Steve remained where he was, already knowing his presence was also required, and idly watched the other ponies leave through the back of the hall.

Once the doors had closed after the last pony had left, Luna addressed the professor. “We are organizing a journey to a star, specifically the star I have brought as close as possible to our world. Accompanying me shall be Princess Twilight Sparkle. We would like to invite you to join us. Steve, here, shall also be accompanying us.”

As surprised as he was by the request, the stallion was outright shocked at hearing the human’s name. “How is such a trip possible?” he asked, not quite daring to gainsay the princess. “What would be the goal?”

“You wish to research the origins of our realm?” Luna asked. “We have reason to believe the stars may provide insight.”

The professor didn’t seem to know what to make of that. “Seriously?”

“Remember how this realm neither expands nor contracts?” Steve asked. “I’ve uncovered evidence the stars are responsible for that. I am certain they are magically manipulating this realm to keep the average energy density at just the right value to keep the size static.”

Arcane Scroll looked at Steve as if for the first time. “You’re a magic-less human… how?”

Luna stepped between them. “Before we can proceed further, you must first be informed of certain royal secrets.”