# Possibility of anti-time

I was just wondering if every particle has an anti-particle (or so I've read/heard), are there other things which could be candidates to have an anti- "form" as well? My example is focused on the possibility of anti-time. Sorry for a weird question. I was just wondering.

• Hint: Wikipedia has an article for “Antiparticle” but not for “Antitime” or “Antispace”. Mar 17 at 23:49

## 4 Answers

Yes, there are some quantum mechanical thingies which serve as their own antiparticle, but the margins of this page are too small to contain a list.

Regarding time, it is neither a particle nor a wave, and so "anti-time" isn't a thing- or a thingy either, for that matter.

In considering antimatter, as with many things in physics, the name my obfuscate the concept. The genesis of antimatter has to do with the symmetries of spacetime: all the fundamental particles we observe are excitations of quantum fields, and these fields must transform under representations of the Lorentz Group. (The representation theory of the Lorentz group is rather involved).

So the electron is an excitation of the electron field, and the electron field is a Dirac spinor field. That means it has 4 components. It needs these 4 components to be self-consistent regarding special relativity. The components correspond to the 2 electron spin states (sort of), and 2 positron spin states. The positron is of course the antimatter compliment to the electron.

When Dirac wrote his equation down for relativistic electrons, he needed these 4-component objects (now called spinors) to get a mathematically consistent answer, but did not know what to do with the positron parts. Fortunately, the positron was observed in cosmic ray experiments a few years later, and antimatter (as a concept) was born.

Quarks are also spin 1/2 fermions and have a similar structure regarding antiquarks. Like electrons vs. positrons, the antiquarks have opposite charges. They also have opposite color charges, which is a whole nother thing.

The book is still open for neutrinos. Being neutral, they may exist as a different type on spinor called Majorana spinors. If this is they case, then they are their own antiparticle, and search for neutrino-less double beta decay, in which the two neutrinos quietly annihilate each other, have been on-going for decades.

Meanwhile, photons are their own antiparticle. This is critical for the function of the electric light bulb (otherwise, it would have to emit anti photons, too).

Regarding time, there is no anti-time; however, time-reversal was once thought to be a symmetry of space-time (the Weak interaction broke that). If you look at the definition of velocity

$$\vec v = \frac{d\vec x}{dt}$$

under time reversal, velocity changes sign and so does $$dt$$, while position remains unchanged, so that:

$$-\vec v = \frac{d\vec x}{-dt}$$

is the same equation and holds true. Velocity is "time-odd", while position is time even ($$T:\vec x \rightarrow +\vec x$$).

Newton's law is time-even:

$$\vec F = m\vec a = \frac{d\vec x}{dt^2}$$

becomes

$$\vec F = \frac{d \vec x}{(-dt)^2} = \frac{d\vec x}{dt^2}$$

One can also look at these equation under coordinate inversion ($$P$$ for parity) with similar results. Like $$T$$, $$P$$ was once thought to be a universal symmetry. The weak interaction broke that.

Nevertheless, we still believe $$CPT=1$$ is must symmetry (Where $$C$$ exchanges matter and antimatter). This is why you often hear "a positron is an electron going backwards in time", but if $$C = P^{-1}T^{-1}=PT$$, then a positron looks like the mirror image of an electron going backwards in time.

Every physical particle has an antiparticle which has all fundamental characteristics of matter opposite. This is a concept attached to matter components like the electron, the proton…

This symmetry of elementary particles was first theoretically discovered by Paul Dirac, and later confirmed through the discovery of the first of them: the positron e⁺ antiparticle of the electron e⁻.

See: Antiparticle

This mathematical symmetry concept doesn't apply to any thing else than fundamental particles.

Thus there is no such thing like anti-space, anti-time, anti-frequency… even if we often consider the change of physical laws when we change them through a mathematical symmetry as for example:

t → -t


( the opposite of time, within which a particle would behave as aging "backward" ).

If we take the time-reversal aspect of CPT symmetry literally, then the missing antimatter is a time-reversal of our matter universe.

In this model, there is an antimatter universe, evolving in the opposite time direction from ('prior' to) the Big Bang - and thus, presumably, inaccessible to us.

Picture the jets that occur as a result of violent events in astrophysics, but opposite in temporal instead of spatial direction.

This is a silly idea, unless it becomes testable.

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• In physics we don't take anything literally without checking the definition, first. The definition of time in physics is "that which the clocks show". Clocks can't run backwards. Problem solved. May 31 at 1:30
• There are cosmological models with such backward-in-time antimatter-dominated mirror universe. PS I only report it here, not arguing about its validity.
– M.S.
May 31 at 16:54