Would that imply that the accepted definition of anti-matter is matter that is moving backward in time?
Granted.
This goes back 60 years to Richard Feynman, who famously showed that an anti-particle could be treated exactly as if it were a particle moving backward in time.
I thought it was Feynman rather than Wheeler who suggested that every electron in the universe is the same one, merely running forward and backward through time from the beginning to the end, but that may be an artifact because the public got the notion through one of his speeches. As a mind-blowing concept this is one that should be used more often by the Time Cube crowd. It can’t be disproven; it can take any interpretation anyone likes; and it’s got solid physical credentials.
But as the Wikipedia quote states, using this to talk about time travel is crackpottery. The equations can be used forward or backward (i.e., with positive and negative signs) but so what? If you really wanted to play with causality, you need to go with imaginary mass. Now you got something. Well, you would if only you had something. But since you don’t, you won’t.
If only! It does not sound “imaginary/hypothetical,” because it is gibberish (as virtually any lay commentary involving “the fourth dimension” always is).
I recall the idea being ascribed to one of his students, rather than Feynman himself.
The concept that there is only one electron in the universe bouncing back and forth in time, however elegant, seems inconsistent with the observed fact that there appears to be a fuckton more electrons than there are positrons hanging around.
So is my impression of what the fourth dimension wrong? I still don’t know if I actually get the fourth dimension yet. The beginning of my OP was just a guess based on the content I have been viewing, for what the fourth dimension is.
“That is not only not right, it is not even wrong!” - Wolfgang Pauli
The really killer deal is that time is a “time-like” dimension, and the others are “space-like.” You can’t simply substitute. I can easily travel fifty feet west, but I can’t travel fifty feet/c futureward.
The math really gets screwy in curved space-time, because spatial dimensions can become slightly “time-like” and time can become slightly “space-like.” This is why mathematicians like Tipler and Penrose and all can come up with rotating cylinders or spinning black holes that bend spacetime trajectories into closed loops… Time Machines.
A lot of these issues come down to “Brother, you ain’t got the math.” (And I sure as hell don’t either! A friend once tried to explain tensors to me, and I walked away knowing less than I had before he started!)
Sometimes time is talked about as the “fourth dimension”, because relativity. So this leads to people comparing time to the spatial dimensions. I think you’ve maybe read someone trying to describe what things would look like if we could see motion through time in the same way we see motion through space, and that’s what you’re getting at here. (At that point we’re not really talking about relativity anymore, but oh well.)
The fourth dimension they’re talking about is time, so yeah, it’d be exactly like controlling time. But that’s not a terribly useful observation.
Well, it’s one understanding of the fourth dimension. The idea you’re talking about is that an object’s duration is a measurable quantity of that object just like its height or width or depth. Duration would be the amount by which the object extends its presence in time.
Actually, it can be disproven. Use a couple of high-energy gamma rays to pair-produce an electron and a positron. Do some measurements on them to confirm they exist and have the proper mass, charge, spin, etc. Then re-annihilate them with each other. Presto, an electron and positron which are verifiably disconnected from all other electrons and positrons in the Universe.
Where’d ya get that high-energy gamma ray from?
A 1920’s style death ray!
Learn all about this one weird trick discovered by a Straight Dope poster that Big Time hates and doesn’t want YOU to know about!
Possibly from annihilation of an electron and positron. Doesn’t matter-- Photons are uncharged, and so the electron line of my created pair is still separate from any other electron line.
And you’re going to let a little thing like that prevent you from claiming that the universe runs backward? !os knith t’nod I
Where’d ya get that electron and positron pair?
(pssst. it’s no use. it’s [del]turtles[/del] one eternal electron all the way down)
Now in my OP I said that you could see the history of how a three dimensional object as moved - basically space-time, because you’re seeing the past. But would you also see the future of how the object is going to move in the fourth dimension?
The reason I am asking this is because I’m trying to understand higher dimensions.
So I am thinking about it in this line of logic:
0th dimension: a point (location)
1st dimension: a line (distance)
2nd dimension: a square (area)
3rd dimension: a cube (volume)
Now you start this cycle all over again. Basically you take the cube, and you think about it as if it’s a point. So if you take two cubes, and connect them (with that thing I was talking about in my OP), then you have the fourth dimension. This can be compared to taking two points and connecting them to go from the 0th to the 1st dimension, except three dimensions higher.
Now what I am asking here is by the line of logic I am using, would you see both the past and the future in the fourth dimension?
Because if you do, then you could keep going on and on:
Going in to the fifth dimension by connecting two time-lines similar to how we connected two lines to go from the first to the second dimension. But what would the fifth dimension be? And this is where I fall apart; I don’t know what to do when I get to this point.
Rather than space-time, it seems you’re really struggling with the concept of dimensions in the first place.
You really don’t have the 4th dimension via your method. You have successive projections of a 4D object in 3 dimensions. It’s not the same thing.
The classic example is taking successive slices of a sphere from one end to the next (i.e. 2D projections of a 3D object). The projections look like circles that gradually get larger, then get smaller.
You can try to ‘connect’ them in 2D, but it doesn’t really work. The analogue to your idea is simply a bunch of concentric circles somehow tied together. At the end, you’ve only visualized a bunch of circles. You only see the sphere because you’re subconsciously thinking in 3D already. If you’re stuck in the 2D world, you can’t actually properly visualize the sphere.
The same flaw exists in your attempted method to project 4D objects into 3D. You’re really just taking individual 3D ‘slices’ of a 4D object, rather than visualizing the 4D object itself.
Worse yet, you’re treating time as a spatial dimension. While that’s not entirely incorrect, it’s also not entirely correct.
As for our universe, as far as we know, there is no “5th” dimension of measure (ignoring string theoretic universes of 10 or 26 dimensions). We can mathematically consider any number of dimensions we care to hypothesize. It doesn’t make them real or tractable to our brains, which really aren’t capable of visualizing more than 3 dimensions (but which can certainly do the mathematics for many, many more), nor does it give them a real analogue in the actual universe.
But what is the the 4D object itself? How would I know if I am visualizing the fourth dimensional object correctly? Even simpler, how do I do it?
I tried watching this video. It goes through all the dimensions from 0 to 10. But even with that I am having a hard time understanding it.
I am not trying to be difficult or irritating. The problem is that I just don’t get it. It’s an extremely hard concept for me to grasp - dimensions above the third, or even, what dimensions are.
I looked up the definition of dimension and I got:
Basically, you can’t actually visualize more than 3 dimensions. I’ve seem some people claim to do it, but I’ve never seen a clear example they accomplished it. The best I’ve ever seen is people taking approximations via slicing.
Notice the disclaimer on the video (the video guy denies it, but the video really is increasingly wrong as it goes on):
[QUOTE=Rob Bryanton]
It has come to my attention that minutephysics claims everything past the two minute point in this video is increasingly wrong
[/quote]
Let me expand on the sphere example a bit.
Let’s say, instead, you have two circular cones glued together at the big ends.
If you do the same thing - take successive slices along he main axis - you still have a bunch of circles.
So, how does the average 2D person know these circular slices came from a sphere and not these cones?
Well, if can somehow take slices not perpendicular to the main axis, you get ellipses instead. But then, how do you know you don’t have an ellipsoid?
Ok, well, the rate at which the circles grow or shrink with different slices should give you a hint.
Fine, except that involves more complicated measurement than mere sight. It’s not “obvious” anymore just from the slices.
In other words, it’s only immediately obvious to you because you’re subconsciously already visualizing in 3D.
The same thing is true in 4D. Your projections assume a ‘preferred’ orientation for your 3D “slices”. Any slight deviations from that orientation produce different “slices” even though they’re all from the same 4D object. We can’t visualize that 4D structure properly with our brains. The slightest shift in how the slices are taken changes our 3D perception. The best we can do is come up with a mathematical description.