Canterlot City, we’re under attack! Scramble!

They’re starting to come through!
I can’t stop it!

Why is Midnight Sparkle shoot magic beams out of her hands instead of her horn?! She has a horn?!

Is Midnight Sparkle trying to bansished or exiled human beings to Equestria and drained all of Equestrian Magic across Equestria because she was trying to destroy both Equestria and the human world, wipe out all live of Equestria and the human world, overthrow Celestia, Luna, Cadance, Shining Armor, and Twilight, and rule Equestria?

now your thinking with portals

@Cirrus Light  
The timespan thing is more of a spiritual aspect than anything, just ignore it if you like.
 
I didn’t say the copy is you, it is definitely a carbon copy, and if you made a copy and you killed me, you did kill me.
 
The mind-body problem has more to do with philosophy, “I think, therefore I am” is personal based. For example, I do not know whether the person next to me thinks the way I do as a person. It’s like being a protagonist in a video game, you the player, are in the game, however there are NPCs, we don’t know if our real world is like that either.  
For all we know, we could be a character who is surrounded by programmed machines, we have no real idea if the other person can think and feel like we do. It’s not like I can connect to someone else’s brain and know what they’re thinking.  
You could apply this to even non-living things, for example, in the Shinto religion, the general belief is that everything has a spirit, everything is alive in some way. However, we wouldn’t know that even if that was true, our classification of living things, does not include spiritual elements.
 
And yes, you would die and the copy would live, but from the copy’s perspective who is acting as you, would continue living as you, as if it was them. From the clone’s view and a third person’s view, they are you, but the only person who cares if you’re actually dead, is you. Not saying this is good or anything or if anyone should actually do this, this is what the situation might be like.
 
(Not at all science, so ignore this is you like, but let’s say reincarnation happened, then your body may have died, but your spirit moved on to the new body, you technically still exist as you. This is all spiritual rubbish, but this would technically be the only way the whole thing would turn out and you are still you.)

@VNagato  
But why is the timespan over which the replication occurs relevant? If I could create a perfect copy (carbon copy, I think, is the term) of you, then I did so, then that copy would be just a copy. Still alive, you’d experience life through your own eyes, not the copy’s. So why is it any different if I kill you as I make the copy?
 
The problem here is the mind-body problem, and it’s a fundamentally unsolvable one. No matter how complex you make any physical system, it should only be a complex physical system, and our perception of reality as it is, simply should never exist by any physical description - “I think, therefore I am” is the only real way we know we exist. A Furby (a talking, robotic doll that was popular in - was it early 2000’s or late 1990’s?) does not actually feel hunger even if it says it does. So no matter how complex you made it, there’s never a line you cross where it should suddenly feel it.
 
There is absolutely no physical, non-arbitrary justification for us to be aware as we are. Awake, yes. Form memories, yes. Respond to stimulus, yes. But actually feeling as we do - no.
 
We don’t know what makes us experience/perceive reality as we do, and this isn’t a problem of how much we know, it is a fundamental problem that cannot be solved, so nothing will ever truly convince me that the re-assembled copy of me is me, rather than just a copy of me.
 
In other words, you fundamentally cannot prove that the copy of you is actually you - you can prove the copy has the same brain, the same memories, etc., but not that it’s actually you, the same being that actually perceived those memories a few years ago, thus, you cannot prove to me that the copying process doesn’t actually kill you, thus, I won’t risk my life on it :q

@Cirrus Light  
There are some ethical reasons why people don’t like that idea, and I can see why. However the way I see it is that it’s a bit different than making a clone.
 
Clones are genetically identical in terms of DNA the time you first extract it from the original, however DNA is always changing, after the clone is constructed, it’s not you, you yourself are still existing and information is being collected, already you are different than your clone just genetically.
 
“You are what you eat” is literal, your DNA is always taking in information and changing, thus why nurture is just as important as nature. Nature is what you’re given, while nurture is a continuous process. So while the base DNA is the same, you and your clone are already separate beings as genetically, the two of you are different.
 
And this part is just really a rant ||but I can’t believe people actually think that if they clone their dead dog that it’d be the same dog. Your real dog is dead, I get it, you feel sad and want them back, but paying a million dollars for a base genetic replicate, whose DNA had already changed because recreation/cloning process in general means it ain’t the same. ||
 
The teleportation theory, in my opinion, is doing the deconstruction and reconstruction almost simultaneously, therefore there are never 2 of you, only one exists, therefore there is absolutely no change genetically and ‘you’ don’t see from your original, ‘you’ see in your new body. That’s how I see it anyway.
 
In terms of every atom/cell in your body being replaced, there’s been a study or something that says in 7 years every cell of a human body has been replaced with new ones, thus why people say (I’m not sure if this is a joke or serious) that if you haven’t seen a person in a very long time, they’re a complete stranger, you don’t know them, they’re not the same person and you don’t have to act like you do know them.
 
Another point is that comparing ratios of the number of your cells compared to bacteria in one’s body, there’s more bacteria than actual human cells. Which brings up the question “Are you really you?”

@VNagato  
Spacetime is like an elephant, in that there are many ways you can describe it. Have you heard the old metaphor of ten blind people trying to describe an elephant?
 
One blind person grabs the ear, and says, “an elephant is a thin, flappy sort of animal.” Another grabs the leg, and says, “no, it is thick and strong like an oak tree.” Another grabs its tail and says, “No, it is thin and brushy, with long hairs.”
 
When describing different properties of spacetime, it can be useful to visualize it in different ways.
 

 
What I had in mind is, if spacetime is like a fabric, and each universe is a different sheet, then you cut off a patch of the fabric on one sheet, then sew it into the other sheet. There would be no tidal forces in this case, but cutting and sewing spacetime doesn’t make any sense in general relativity (GR) - GR describes spacetime as a curved geometry, but says nothing about any ability to “tear” it, or even worse, to “sew” it into another space. So that part would have to be magic / some physics not yet known to mankind :p
 

 
The form of teleportation you describe could, though, in theory, allow you to move through any zone with tidal forces. After all, if you’re torn apart into constituent atoms, then you’re already dead, and tidal forces re-arranging that organic powder isn’t really going to do much, so long as it’s nicely re-built on the other side.
 
But that sort of teleportation has always bothered me - it nails on to some really deep and impossible questions about the nature of reality and our experience of it. Isn’t that effectively killing yourself and just making some copy that’s identical to you, but not “you”? Wouldn’t you experience death if you did that?
 
The counter-argument is that every atom in our body is slowly replaced - it’s an old thought experiment of a ship that has individual pieces replaced until every part of the ship is made of new parts, and no original parts remain. Is it the same ship anymore?
 
While whether it’s the same “ship” or not is purely a matter of how you define things, our own conscious awareness of reality is not. If I make an identical copy of myself, I don’t see reality through my copy’s eyes, I still experience reality through my own eyes, so if you kill me, I’ll still die, and my copy will exist, but I will be dead.
 
Same applies to this de-construction and re-construction method of teleportation, hence why it’s never been one I never particularly liked :q

@Cirrus Light  
I try to apply Taoist-like philosophy and some mediocre science knowledge for possible explanations, at least you know physics enough to try to apply it to something confusing as this xD
 
But we can say time-flow could change, correct?
 
Could we say that they did teleport though? Teleportation doesn’t yet exist, so this is all theoretical, but I hear the theory is that at one end they copy all the body’s information, send the information to the other end, where a new body is constructed and at the same time the old one is destroyed.
 
This isn’t exactly the same, but say the body went through the portal, was deconstructed into information(or molecules idk) and then a body was reconstructed at the other end of the portal. This could be a reasoning behind why they change from being horses to human-things, since their new bodies was reconstructed, but could this be a way to avoid being crushed by the forces? Is this what you meant by teleport?

@VNagato  
It’s a fantasy show. I am well aware that I’m applying physics to a fantasy cartoon, but it’s just so fun that that doesn’t stop me :P
 
But yes, your first paragraph pretty much sums it up.
 
You could just say that Equestrian magic changes the time-flow of the world…
 
But then the issue is going in-between the two worlds when the time flow was different (Shimmer’s first jump).
 
However, if she teleported, it could work…
 
Think of the rate that time flows like the elevation of the ground. If you go from lower ground to higher ground, then that implies you went uphill at some point. That sloped ground would be the gravitational gradient.
 
But if you don’t cross a portal, but instead teleported, then it could be akin to riding an elevator up, where it never slopes because you lift the ground with you.
 
It’s the metaphorical slope that’s deadly.

@Cirrus Light  
Although most of what you said is pretty much ??? to me, but if the time flow of Equestria is just a bit different than Earth’s the gravitational force of the portal between them is incredibly powerful?
 
And as you said, Friendship Games seems to show that the time flow between the 2 worlds are the same, however, could some type of interference cause a very slow and gradual change in time flow for that world?  
For example, my fanon is that Sunset Shimmer was Celestia’s student, let’s say for example, 10 years ago, but when she left for the human world she only experienced something close to 4 years. However when Equestrian magic was used in the human world, it disrupted the physics of that world to slowly match up with Equestria’s thus why time flow by the time in Friendship Games look relatively the same.
 
I’m sorry if this just all sounds like fantasy rubbish, but I can’t bring myself to believe that Sunset left Equestria for only about 4 years, when it appears she and Twilight are about the same age, and Cadence was present at the time, or that the sirens can live for about 1000 years.

@Cirrus Light  
Are you the brony reincarnation of Carl Sagan? :P

@Scrounge  
If the portals were to some random point in deep space, then she could’ve drained Earth’s atmosphere :p
 
Which brings me to the realization that Equus and Earth must have the same atmospheric pressure.
 
Arg! Noooooo! I reject this! This is terrible and drives me mad. Sure, lower gravity could explain Pegasus flight, but only a thicker atmosphere could explain how airships work as they do in Equestria! But no pressure differential in the portals creating wind…
 
Maybe the portals went somewhere super hot in Equestria, like, 120°F, and it was a really cold evening in human world, like, 30°F, so they had different weather-dependent densities but equal pressure thus no wind…

@Background Human  
One is a carefully-made portal between dimensions. The other is a bunch of holes ripped through the fabric of time and space that could potentially destroy the world.

@Background Human  
It actually depends on a few things… One is the spacetime structure of it.
 
You see, you don’t actually feel gravity at all. The astronauts on the space station are under 96% the gravitational strength we have here on the surface of the Earth. The reason they’re weightless is that they’re in free fall.
 
Likewise, you don’t actually feel a gravitational force, because everything falls together so there’s no squishing or pulling. But you do feel “Tidal Forces.”
 
Tidal Forces are this: let’s say we have a person standing over a black hole. A black hole with Earth’s mass would be 3 mm in radius (r = 2GM/c^{2). About 1000 times the black hole’s radius away, newton’s gravity actually works well enough as an approximation. But we can use 2,000 times further away for good measure.
 
Newton’s gravitational force strength:  
F/m = a = g = GM/r}2.  
G = 6.67e-11, M = 5.97e24 kg.
 
Earth’s radius is 6,370 km, so, plugging that in for r, we can confirm this equation works since we know 1g = ~ 9.8 m/s^{2:  
F/m = g = GM/(6,370,000)2 = ~9.8 m/s2
 
For 6 meters, that’s F = 1.1e13  
For an average 1-meter tall pony, if her hooves are at 6 m, her horn will be at 7 m:  
F = 0.8126e13
 
Her hooves will feel 0.3174e13 = ~ 3,174,000,000 km/s}2 faster acceleration than her head. As you can imagine, this is not particularly healthy.
 
Also, her right shoulder and left shoulder will both be pulled towards the center of the black hole. Since from her right shoulder, the black hole would be down and to the left slightly, and for her left shoulder, down and to the right slightly, the “left slightly” and “right slightly” parts will push her shoulders together with, again, some vastly powerful force.
 
Now, on the real Earth, we don’t notice this much because we’re at such a great radius (fortunately, since the mass is all the ground, the equation is no longer valid under the Earth’s surface, so the strongest gravity gets is at the surface).
 
At 6,370,000 meters, it’s 9.81344 m/s^{2, and at 6,370,002, it’s 9.81343 m/s}2, so the difference is 0.01 mm/s^2 - so tiny, that you would need a very precise instrument to detect it.
 
Nonetheless, the black hole example shows how tidal forces can be quite extreme in strong gravity.
 

 
So, here’s an interesting thing, though; if there’s no tidal forces, then that means there’s no gravity. That gets into some more advanced nuances in the general theory of relativity, but if there’s no tidal forces, that really means that you’re just looking at the thing in a funny frame of reference, and there’s nothing really there. Tidal forces show you there’s a real gravitational field, and if it’s transporting you into another dimension, it’s definitely real.
 
So there will be tidal forces, and if one universe is flowing at a different rate than the other, she will have to feel them in order to cross from one into the other. (Lol, that tunnel scene actually becomes really grimdark if you take the warping seriously and consider that her body is being mashed up terribly. Lol, I don’t think it would be painful, though - the screaming must be some other physiological effect, because I think massive tidal forces would turn your brain to mush so she couldn’t be conscious until her body is re-assembled on the other side. But, I dunno, maybe the brain is more resilient to tidal forces than that. You’re kind of getting into unknown territory, here, since IRL we don’t have any examples of raw spacetime curvature warping things to see how it effects physiology. Blunt impacts move things around differently based on their density and force transmission, etc. etc, so there’s really no analogue.)
 

 
Mmmmmm, but forgive me. I said in my comment here that if I took in the CMC I’d cruelly teach them things. I’ve really just taken this opportunity to talk about science, because the direct answer to your question is a lot simpler… If time flows at the same rate in both universes, then there’ll be no gravitational forces at all (test: what does this say about tidal forces?) as a result of crossing from one to the other.
 
But, a wormhole does have its own effects. Remember “Interstellar,” when they went through the wormhole, that scientist told the engineer protagonist to let go of the controls, the craft would fly through on its own? That’s accurate. But how lethal that may or may not be all depends on the properties and structure of that particular wormhole.
 
Given this scene from “Friendship Games,” though, the lack of a gravitational gradient implies that time flows at the same rate in both worlds.
 
And you’d see it - although you don’t feel gravity, it does move you, and the tidal forces would be compressing or decompressing air, creating anything from a strong wind to a nuclear explosion, depending on how intense it is.

@Cirrus Light  
Okay, so here’s my question. In the first movie we see that the mirror doesn’t bring Equestria and Humanland together the way the portals above do. It leaves some distance between them–that glowy Doctor Who tunnel.
 
 
Would that distance do anything to mitigate the gravitational field, and if so, how long would the tunnel need to be for the gravity to be tolerable? (About 5 g’s for an untrained human; don’t ask me about pony physiology.)

@Cirrus Light  

 
RIP

@Silv_4740  
Millions of times stronger than that :p
 
If it’s like Narnia, where many years are a few seconds in the other world, then the gravity could be so intense it’d probably cause the air to condense so intensely that it will undergo nuclear fusion.
 
If time goes 1.0001x as fast in Equestria, then a portal to there might condense the air so that it heats so intensely it’s akin to a constant big explosion…

@Cirrus Light  

 
Strong enough to crush people?

@Silv_4740  
No. Just incredibly strong.

@Cirrus Light  

 
So, the gravity would be equivalent to a black hole?