Proof That the Universe is Electrically Neutral

[Moneer81]

What evidence do we have to support the assertion that the universe is electrically neutral on large scales?

I know that gravity is the dominant force on large scales but what kind of evidence can we give to support the above statement? Does it suffice to say that we have the same number of protons and electrons?

 

[shemszot]

Just out of interest.. Is there a theory that states that the universe is electrically neutral?

 

[Moneer81]

Just out of interest.. Is there a theory that states that the universe is electrically neutral?

Well not a theory maybe but we know that the universe is electrically neutral. You don't suspect we live in an ionized universe, do you?

 

[shemszot]

It's all a question of quantities. I don't suspect the universe is significantly ionized, however I don't see any proof to suggest that the universe is completely balanced either. If there was a very insignificant number of charged particles of one type which would be more common in the universe would we really know? As a matter of fact I have previously though about what exactly would happen if there was a slight charge to the universe. If you take on this though experiment some interesting conditions arise.

 

[Moneer81]

It's all a question of quantities. I don't suspect the universe is significantly ionized, however I don't see any proof to suggest that the universe is completely balanced either. If there was a very insignificant number of charged particles of one type which would be more common in the universe would we really know? As a matter of fact I have previously though about what exactly would happen if there was a slight charge to the universe. If you take on this though experiment some interesting conditions arise.

Well maybe I didn't mean "proof" but instead I meant "evidence"

It seems to be an agreed upon fact that the universe is electrically neutral, on large scales.

What's the evidence? One way to think about it so to try and answer the question that you asked: What would happen if the universe wasn't neutral? How would the universe be like then?

 

[cadnr]

I guess you might not have heard of the IGM (intergalactic medium) which could be considered to constitute the majority of the universe. The IGM is ionised.

I don't think there is any good observational evidence that the universe is charge-neutral.

I'd be interested to hear from anybody in the know who can say whether charge-neutrality of the universe is a feature of the hot big bang theory.

 

[Riogho]

Well, I think we assume the universe started out with no charge, so tehrefore when particle decays took place (pair production) and split into a positron/electron, and such things.

Conservation of charge?

 

[Wallace]

There seems to be a lot of confusion in this thread. To clarify, the Universe is indeed mainly ionized, and has been for many Billions of years ( look up 'epoch of re-ionization' for more info). This, however, has nothing to do with whether the Universe is electrically neutral. If something is ionized that simply means the positive and negative particles (atomic nuclei and electrons) are separated. It doesn't mean that the overall charge is not neutral. The total charge of something (including the Universe) is a completely separate issue to the ionised fraction.

 

[cadnr]

So is the universe charged or not?

 

[sysreset]

So is the universe charged or not?

I don't think anyone knows on very large scales (greater than 10^9 light years).

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V3S-4C76BVX-8&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=de8193723d84e10ebf0e09af45371bf2 suggests that locally, in the vicinity of the Milky Way galaxy, on a scale of 10^5 light years, space is dominated by ionized gas. I haven't seen anything yet that suggests that postively ionized gas has been found over here and negatively ionized gas has been found over there. Since the universe is mainly ionized, I would have to conclude that locally, on a scale of 10^5 to 10^7 light years, it is also electrically charged, unless observations of opposite ionization have been made...fill me in if those observation have already been made...

If the universe is electrically non-neutral out to a scale of over a billion light years, what are the implications? Where are the missing electrons (or atomic nuclei)?? Were they ever there? This seems like a very fundamental question that should be discussed and resolved or very basic models are seriously flawed.

 

[marcus]

I guess you might not have heard of the IGM (intergalactic medium) which could be considered to constitute the majority of the universe. The IGM is ionised.

I don't think there is any good observational evidence that the universe is charge-neutral.

I'd be interested to hear from anybody in the know who can say whether charge-neutrality of the universe is a feature of the hot big bang theory.

There seems to be a lot of confusion in this thread. To clarify, the Universe is indeed mainly ionized, and has been for many Billions of years ( look up 'epoch of re-ionization' for more info). This, however, has nothing to do with whether the Universe is electrically neutral. If something is ionized that simply means the positive and negative particles (atomic nuclei and electrons) are separated. It doesn't mean that the overall charge is not neutral. The total charge of something (including the Universe) is a completely separate issue to the ionised fraction.

Wallace has clarified the issue here. There is the question of overall neutrality.

Cadnr and presumably almost everybody here knows that the universe is largely ionized. So that has no relevance to the issue of overall neutrality.
Sysreset offered evidence that there is some ionized gas somewhere, but that is irrelevant. It does not indicate that the ionized gas fails to be overall neutral.

We all know the interior of the sun is largely ionized----most of the hydrogen nuclei and the electrons are running around separately instead of being paired up in atoms. BUT THE SUN GIVES EVERY SIGN OF BEING overall NEUTRAL.

In science when you make a statement it is supposed to be true within some errorbar or within some tolerance. So Cadnr, would you be happy with an assurance that the universe is neutral WITHIN ONE PART PER BILLION? What would satisfy you?

Can anyone tell us what would happen if the sun had one ppb too many electrons?

Can anyone estimate what would happen if our Milky Way galaxy had one ppb too many protons?



For that matter, how about if the Milky Way deviated from electrical neutrality by one part per trillion?

this is a simple back of envelope calculation. It would be exploding. we can go higher, but I don't know how close to perfect neutrality Cadnr wants.

 

[sysreset]

Hi Marcus,

Are you saying you have proof that the Milky Way galaxy is electrically neutral, to, say, one part per quadrillion? Since it is largely ionized, there must be structures that are negative and some that are positive to balance it out. On what scale are these separately charged structures, and has anyone attempted to create an image of this, for our galaxy or any other galaxy?

 

[marcus]

... Since it is largely ionized, there must be structures that are negative and some that are positive to balance it out. ..

Why?

I'm not sure what you have in mind by "structures". You speak of mapping. I assume you mean some macroscopic structures that would be visible on a galaxy map. Maybe you could be more definite about what structures you mean and why you think they must have a net electric charge.

 

[Wallace]

Since it is largely ionized, there must be structures that are negative and some that are positive to balance it out.

Your conclusion does not follow from your premise. If a gas in ionized it simply means that some electrons have separated from the constituant atoms (or molecules) that make up the gas leaving positively charged atoms/molecules and negatively charged electron. However they are still mixed together in the same gas, the 'seperation' that you assume does not exist. The positive and negative charges still mingle in the same space. Even if you took a very small volume (the size of a grain of sand) of an ionized gas the overall charge is still neutral.

 

[sysreset]

I get it now, thanks. You've answered my question marcus and wallace.

 

[kamerling]

In science when you make a statement it is supposed to be true within some errorbar or within some tolerance. So Cadnr, would you be happy with an assurance that the universe is neutral WITHIN ONE PART PER BILLION? What would satisfy you?

Can anyone tell us what would happen if the sun had one ppb too many electrons?

It would blow up with a bang that would make a supernova look like a firecracker?

The mass of the sun is 1.99×10^33 g, so it has 1.99^10^33 * (6.022 * 10^23=avogrado's number) = 1.24 * 10^57 Electrons. This is a charge of about 2*10^38 coulomb (assuming everything is hydrogen) using a 1 ppb surplus we still have 2*10^29 coulomb of charge. The repulsive force due to this is (charge of the sun)*(coulombs constant)/[(mass of sun)*Gravitational constant] which is about 10^16 as big as the gravitational attraction.

I think it's safe to say that the charge imbalance of the sun must be < 10^-25.

It seems likely to me that the sun probably has a small positive charge, because it's easier for electrons in the solar wind to get away than for heavier positively charged ions.

 

[Chronos]

We have good evidence there is a slight imbalance in the total charge of the universe. If the universe was charge neutral, matter would be nearly extinct by now. Quantum uncertainty does not permit a static universe.

 

[Brad_Ad23]

We have good evidence there is a slight imbalance in the total charge of the universe. If the universe was charge neutral, matter would be nearly extinct by now. Quantum uncertainty does not permit a static universe.

Just out of curiosity what sources are there for this, and just what do you mean by a slight imbalance? i.e how slight? 1 part per quintillion?

 

[Wallace]

We have good evidence there is a slight imbalance in the total charge of the universe. If the universe was charge neutral, matter would be nearly extinct by now.

Can you elaborate Chronos? This doesn't sound right to me. Can you indicate where you got this from?

Quantum uncertainty does not permit a static universe.

I'm not sure how we suddenly got to a static universe in a discussion about whether it has a neutral overall charge??

 

[xantox]

What evidence do we have to support the assertion that the universe is electrically neutral on large scales?

Amongst others, there is the evidence of CMB isotropy. A charged universe would feature currents which would show up in the spectrum.

 

[Haelfix]

We see mostly isotropy, so the amount of free charge floating around is bounded pretty strongly by experiment.

Its usually an *assumption* in simple models

 

[Lawrence B. Crowell]

Assume the universe had a net electric charge. What would happen? Think of the lines of electric force. These lines would wrap around space and would find no charge to connect up with. They would wrap around infinitely and the density of the electromagnetic field energy would diverge. This would happen if the universe contained only one excess electron. This is a physical situation which is unacceptable.

Now think of a system of harmonic oscillators. If there is a driving frequency which is resonant with the system it will diverge --- the Tacoma Narrows bridge. Therefore for the system to be well behaved the driving frequencies of the system must be orthogonal in state space from the natural frequencies of the oscillators. The oscillators are the quantum states for photons, which are complete. Therefore there must be no general driving force for the system of oscillators. There is then no cosmological net charge which can drive the system to a divergence. The universe is electrically neutral.

Lawrence B. Crowell

 

[Wallace]

Assume the universe had a net electric charge. What would happen? Think of the lines of electric force. These lines would wrap around space and would find no charge to connect up with. They would wrap around infinitely and the density of the electromagnetic field energy would diverge. This would happen if the universe contained only one excess electron. This is a physical situation which is unacceptable.

It sounds like you are assuming the Unvierse is finite with a compact topology (i.e. allowing field lines to 'wrap around). This isn't neccessarily true for the Universe. In any case I don't find this argument compelling. There is no requirement for fields lines from a charge to 'connect up' with any other charge? The Universe contains only matter with a positive gravitational 'charge' and suffers from no such cataclysmic problems as suggested here.

Now think of a system of harmonic oscillators. If there is a driving frequency which is resonant with the system it will diverge --- the Tacoma Narrows bridge.

A resonant oscillator does not 'diverge'. The frequency response curve of, in your example, the Tacoma Narrows Bridge is finite at all values of the driving frequency, including at the resonant frequency. The only reason the bridge 'diverged' so to speak is that the forces holding it together were less than the maximum restoring force needed for the amplitude of oscillation at the resonant frequency.

Therefore for the system to be well behaved the driving frequencies of the system must be orthogonal in state space from the natural frequencies of the oscillators. The oscillators are the quantum states for photons, which are complete. Therefore there must be no general driving force for the system of oscillators. There is then no cosmological net charge which can drive the system to a divergence. The universe is electrically neutral.

Lawrence B. Crowell

The static electric field of a point charge, being static, cannot be the driving force of an external quantum oscillator. I don't see how any of the points you make above are related to this issue, or in fact have much meaning? You might want to explain more clearly?

 

[Chronos]

http://daily.stanford.edu/article/2004/8/12/slacPhysicistsMaySoonAnswerWhyUniverseOnlyConsistsOfMatter
http://www.sciencedaily.com/releases/2006/06/060624115839.htm
http://www.physorg.com/news88684585.html
http://arxiv.org/vc/physics/papers/0604/0604002v1.pdf

 

[Wallace]

Those links are on the issue of the imbalance between matter and anti-matter, not the issue of any imbalance between positively and negatively charged matter. These are very separate issues.

 

[sysreset]

Amongst others, there is the evidence of CMB isotropy. A charged universe would feature currents which would show up in the spectrum.

I think it would be flawed logic to use CMB isotropy to disprove an electrically charged universe now. CMB data reflects the state of the universe 13 billion years ago. I think that after 13 billions years charge neutrality could have been lost via interactions between ionized matter and black holes, or through other mechanisms, and we wouldn't know this by looking at CMB.

 

[xantox]

I think it would be flawed logic to use CMB isotropy to disprove an electrically charged universe now. CMB data reflects the state of the universe 13 billion years ago. I think that after 13 billions years charge neutrality could have been lost via interactions between ionized matter and black holes, or through other mechanisms, and we wouldn't know this by looking at CMB.

It is of course entirely correct that the CMB is not -definitive- evidence that the universe is neutral. As always in cosmological observations, which only sample a small portion of space and time, there is an inherent uncertainty which is moreover accompanied by the fact that you need to make the very specific assumptions of some particular physical theory to bring an interpretation to the data.

However, this still counts as valid evidence to provide a better large scale constraint than say, an experiment conducted in laboratory. The underlining theoretical assumption, which cannot be counted as a flaw, is in this case that the electromagnetic gauge symmetry of the standard model would not have been broken after recombination.

 

[Haelfix]

" I think that after 13 billions years charge neutrality could have been lost via interactions between ionized matter and black holes, or through other mechanisms, and we wouldn't know this by looking at CMB."

That won't work, you still can't 'create' charge with ionizing matter, nor will black holes work either (since net charge is also conserved in black hole processes by the no hair theorem).

You either have a net charge imbalance right at the start of the universe, or you don't at all. Like others said, that's strongly constrained by experiment.

 

[xantox]

You either have a net charge imbalance right at the start of the universe, or you don't at all.

Again, we should be prudent not to go beyond both extremes of the constraint. Mechanisms could still exist allowing a charge imbalance to develop over cosmological timescales. Numerous such proposals were worked out, implying more or less exotic assumptions and/or theories beyond the standard model (eg electrons escaping the Randall-Sundrum brane, and many others).

 

[Haelfix]

Yes, that's true. But since we are talking mostly conventional cosmology, that's the way it goes.

 

[sysreset]

Cosmic rays have been observerd to be 90% protons, 9% helium nuclei, and 1% an assortment of heavier nuclei. With all of these positively charged particles flying around without electrons, doesn't it follow that the universe is not charge-neutral; or, if it is neutral, that charges are separated by cosmic distances?

 

[Wallace]

No, this difference is due to the mechanisms that accelerate different types of objects to different energies. The electrons are there, they just aren't traveling with the same energy.

 

[cadnr]

So why is the universe neutral?

 

[sysreset]

No, this difference is due to the mechanisms that accelerate different types of objects to different energies. The electrons are there, they just aren't traveling with the same energy.

Do you have any sources to back up the assertion that electrons are present in cosmic rays to charge neutrality? My understanding has always been that 99% of cosmic rays are hydrogen and helium nuclei stripped of any electrons of any energy, and are thus positively charged particles. http://imagine.gsfc.nasa.gov/docs/science/know_l1/cosmic_rays.html explains further.

 

[Wallace]

You misunderstood, I agree that cosmic rays are mainly protons or other light nuclei (or high energy photons). The key point relating to this discussion is the sentence 'striped of any electrons'. The electrons still exist, so the Universe is charge neutral, but the electrons don't get accelerated to cosmic ray energies. When I said the electrons are there I just meant they are still in the Universe, not that they are in the cosmic ray flux.