The universe has no "up"


Sounds like my romantic life.

Do we have a direction of movement in relation to the cosmic background radiation? It would be as absolute a direction as possible, it seems. But be useless for navigation when I steal the enterprise.


All those big pictures for cosmic background radiation are 360 degree views… so yeah away from it or towards it… or both.

ETA Brian Cox having a say about it on QI





Yeah, but even then, about half the ships they encounter should be “upside down”.


That was also the key to the resolution in STII:TWOK. Khan was thinking two dimensionally in a three dimensional space battle, and it led to his downfall.


Every point in the current universe was at the Big Bang. The expansion of the universe is like the expansion of the surface of a balloon, but that common analogy is slightly misleading. There is no inside to the universe like there is with a balloon, and the expansion isn’t driven by internal pressure, but by an as yet little understood expansive force (proposed candidates include but aren’t limited to the cosmological constant, quintessence, or dark energy) that emerges from the the vacuum itself.

This force - which we call a scalar force because it scales with distance but exerts uniformly in all directions (meaning it has no vector the way a vector force like gravity does) - is very weak, but it’s strength is cumulative in that the further apart two galaxies are, the more space and therefore the more expansive force there is between them, which is why more distant galaxies accelerate away from us faster than nearer cosmic neighbors. That is to say that it’s not a force mediated by waves and particles the way electromagnetism, the weak nuclear, the strong nuclear, and (probably) gravity are; rather it’s a pressure created by the expansion of space itself. If it has a minimum quanta, it’s not a particle which moves through space, because it’s the quanta of space. Quantum mechanics says that there is a smallest unit of space which has physical meaning. You can think of the “fabric” of space, and thus the expansive force as the constant increase of these units.

So the Big Bang wasn’t in a particular place in the universe, it is the entire universe…even the regions that are already so far away from us (and us from them) that light-speed signals starting out now from here or there will never meet. Because although nothing can move through space faster than the speed of light, the expansion of space itself has no such limit. We say such distant regions are beyond our cosmological event horizon (and we theirs), because events from them are cut off from us, and vice versa. At one point they were in the same point as us, because the entire universe was only one point (the singularity at the beginning of our spacetime), but the expansion has taken them beyond our horizon, and more matter gets pushed beyond it by the expansion of space all the time. Eventually, in our universe’s Deep Time future, the expansion will (we think) isolate every wave-particle from every other as everything decays and spreads out. Cosmologists call this the Big Rip (I’m not making that I up, I promise).

You might be wondering about theories like Braneworld Cosmology which hypothesize that our universe is a 3 dimensional “sheet” embedded in a higher dimensional sheaf of universes called the Bulk. You may understandably wonder if there’s a preferred axis within the Bulk. While there may in fact be, this still does not give any special axis to our 3D universe, because that hypothetical fourth spatial dimension would be equally perpendicular to all three spatial dimensions, just as the third spatial dimension is equally perpendicular to both the first and second spatial dimensions. If you set a ream of paper on top of a sheet, it doesn’t give the two dimensions of the sheet any preferred direction or special axis.

There is only one sense in which our universe has a preferred direction, and that is the Arrow of Time. Everything moves away from the Big Bang through time. Since the further out we look with telescopes, the longer the light we see took to reach us at the constant speed of light, we are actually looking at the distant universe in the past. The Cosmic Microwave Background radiation is the red-shifted (by that expansion of space) light from the time a mere 400,000 years after the Big Bang when the plasma in the then much smaller universe cooled enough to combine into atoms which released the light. The distribution of that plasma, and thus the light it emitted when it’s electrons and protons coupled for the first time into atoms, was determined at the moment right after the Big Bang itself.

TL;DR - The Big Bang was everywhere, so there is no away from it in space. No preferred spatial direction. Only preferred direction is the Arrow of Time (past to future). Hypothetical higher dimensions are by definition perpendicular to all three observable space dimensions and thus do not give a special axis to any of them.

:game_die: Would You LIKE to Play a Game? :video_game:


The important thing, though, is that the Big Bang is a point in spacetime far in the past. It doesn’t correspond to any point in present space better than any other, for like TobinL says all of them converge to it as we look into the past. So away from the big bang isn’t an ordinary direction of movement, it is toward the future.

People sometimes compare the expansion of the universe to dots on a balloon as it blows up; they all move apart without any being the center. The thing that others ask, though, is what then is the middle of the balloon. The answer is nothing, that is something outside the universe only made up to help visualize things. That’s kind of an abstract answer, though.

So long as the universe is expanding, I think it might be better to illustrate the balloon with past spacetime in the middle. Here’s a really quick picture I made with that idea; I’d be interested to know if it helps explain this to anyone:

ETA: looks like quick wasn’t quick enough, and GulliverFoyle covered most of this well, but maybe it’s helpful to leave anyway.


Just about. (Though Crusher Joe, I believe, did not.)

But I always operate on the assumption that the Plot Constant is in effect for those universes.


I think your explanation was more succinct :slight_smile:


And Rufferto?


What did you expect?


That’s why it was somewhat refreshing that in at least one shot of the Death Star in the Rogue One trailer, we got to see it “upside down.”

Then again, in other shots we do seem to see it (and all its attendant ships) “right-side-up” in the same orientation for no apparent reason, just like in the old movies.

When I was younger and used to think there might be some theoretical center of the universe from which everything might have emanated (even one that could conceivably be visualized as a point in now-space toward which all outgoing vectors might point if reversed), I liked to imagine that a visitor to that spot might find a loose thread dangling from a spent party popper:


Then you are truly in tune with the universe. Top notch work there!


Depends how you interpret the question. Might be a scientific/philosophic jumping off point!


Then let’s spend our last minutes playing Hucka-Bucka-Beanstalk with Floyd.


There is no centre though. It’s like being on the surface of a ball that someone is inflating. You and your buddies on the ball are all moving away from each other but theres on centre of the surface of the ball.


A better adaptation of HGTTG?


And it always struck me as a weakness of the movie that that would be considered a crucial plot point. I mean of course anybody piloting a spacecraft wouldn’t be limiting themselves to thinking in 2D. As if after centuries of spaceflight and space combat Kirk is the first captain to come up with that. Pshaw.


The way I took it was not that Kirk was the first, but that Khan had presumably learned the art of warfare on a comparatively two-dimensional field of battle (Earth’s land, seas and air) before he was frozen and exiled into deep space, and consequently was unconsciously bringing those biases to a space battle. Since Khan and his acolytes presumably had little to no experience in space combat, it didn’t seem that far fetched to me. As Spock even says, Khan was intelligent, but inexperienced.

ETA: Likewise, it might not have occurred to Kirk to exploit this weakness until Spock pointed it out, because Kirk wasn’t used to fighting inexperienced foes. In a sense, Khan’s own inexperience made him more dangerous, but also more vulnerable, because he made unexpected mistakes.