# We know that there are opposites all around us with energy, you have

1. Mar 6, 2009

### redhedkangaro

We know that there are opposites all around us with energy, you have positive and negative. With matter there is anitmatter. My question is what is the opposite of space and what is the opposite of time, and can anyone talk about what these opposites are?

2. Mar 7, 2009

### Chalnoth

Re: Opposites

The opposite of <- is ->.

3. Mar 7, 2009

### Nabeshin

Re: Opposites

Antimatter v. matter is an extension of the positive vs. negative charge concept. There really aren't that many opposites, and even if there were, there is no reason to think they extend to dimensions (like you ask, space and time).

4. Mar 7, 2009

### Chalnoth

Re: Opposites

Well, the anti-matter/matter symmetry stems from an observation of the CPT symmetry. With space time, application of the CPT transformation inverts space and time (so that forward in time is now backward in time, the +x direction is now the -x direction, etc.).

5. Mar 7, 2009

### Nabeshin

Re: Opposites

Yeah but these aren't really opposites in the sense that positive and opposite charge are opposite... They're negative, but I wouldn't say opposite the way the word is tossed around with respect to something like charge. It's a really ambiguous term, and I would avoid applying it to spacetime because then people want to start throwing around phrases like antispace and antitime and things get out of hand quickly

6. Mar 7, 2009

### Chalnoth

Re: Opposites

But that's exactly what it is.

Well, then I could just point out that anti space-time = space-time.

7. Mar 7, 2009

### Nabeshin

Re: Opposites

Here's my thinking, respectfully:
Spacetime is a 4-dimensional subspace spanned by 4 unit vectors in hte directions {ct,x,y,z}. This obviously covers all x, y, z, and ct, both positive and negative values. So what does it mean to talk about negative spacetime? Simply a flip in the coordinates? If you define opposite to be the additive inverse, then sure...

But if you take opposite to more generally mean an antonym of something, then clearly a term such as the opposite of space is silly and undefined; what could the antonym of a 4-d subset be? The absence of a 4-d subset? Maybe... I only bring up this point because it seems more the definition the OP was going for, because clearly you can say the opposite of x is -x, but to ask what is the opposite of numbers is a whole other question entirely.

8. Mar 7, 2009

### Chalnoth

Re: Opposites

Well, you mentioned matter and anti-matter, which quite literally stem from this precise symmetry (plus the charge symmetry). So yeah, this is exactly what I mean.

I don't think there's any consistent, unambiguous way to do this.

9. Mar 7, 2009

### Nabeshin

Re: Opposites

Alright, good. I think we're on the same page now

10. Mar 14, 2009

### apeiron

Re: Opposites

The are two senses in which things can be opposite - symmetrical and asymmetrical.

So postive and negative charge are symmetrical opposites - mirror image. But then you have the metaphysically deeper form of opposite in which two things are completely unalike, rather than merely flopped in different orientations.

So for example, location and motion, or substance and form, or chance and necessity, or stasis and change, or local and global.

Space and time are this second complementary kind of opposite. Space is our co-ordinate system for measuring all the stasis, all the location. Time is the co-ordinate system we use to capture all the motion, all the change, all the development.

So time and space are opposites. First we completely pin things down, then we allow them to move.

You can find simple symmetry opposition within a spatial dimension. Go two feet in one direction, then go two feet it the opposite.

But time of course has an arrow and is not simply reversed (except in some simplistic human models).

The reason for time's asymmetry is because we have abstracted all the complexity to make the spatial dimensions very simple places. And the temporal dimension contains all that complexity now.

Last edited: Mar 14, 2009
11. Mar 14, 2009

### Chalnoth

Re: Opposites

Except only symmetrical opposites are well-defined. An "asymmetrical" opposite is arbitrary and subjective.

12. Mar 14, 2009

### apeiron

Re: Opposites

I would certainly agree that symmetry is mainstream, and asymmetry is poorly understood by mainstreamers. You would have to go out of your way to learn about it.

Would you say that symmetry-breaking is an arbitrary and subjective subject though? Or the concept or orthogonality? These are some of the many faces of asymmetry.

And there are some concrete models in fractals for instance. The axis of scale symmetry in fractals is in a useful sense the "plane of reflection" for asymmetry.

It is just one of those curious features of physics that symmetry is celebrated as "beautiful" - pure and well-defined, the explanation of everything. Yet look closer and actually it is always asymmetry they are talking about. The broken symmetry which actually produces worlds.

So if you find asymmetry subjective and arbitrary, is that just because you have been focused on the wrong part of the story?

13. Mar 14, 2009

### Chalnoth

Re: Opposites

It has nothing to do with that. It's just that a symmetrical opposite has a definite meaning. An asymmetrical opposite does not. The problem is that an asymmetric opposite could, in principle, be anything at all that is not the thing in question. It's just not a well defined term.

No. It just means that the symmetry in question no longer holds. Symmetry breaking is an interesting and complex subject, and probably has quite a lot to say about how the low-energy laws of physics came to be what they are. But adding on fluff terms that have no definitive meaning like "asymmetrical opposite" don't help.

14. Mar 14, 2009

### apeiron

Re: Opposites

Oh dear. Just because you don't understand something does not mean it is all fluff and nonsense. Do you always take this attitude to domains you have not studied?

15. Mar 15, 2009

### Integral

Staff Emeritus
Re: Opposites

Thread locked. This is pure and meaningless specultation.

Note that not a single advisor or mentor has contributed to this thread. This is a bad sign.