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Environment & Science

How a fifth force of nature went unnoticed by physicists, until now

Four known forces determine behavior of all things in the universe, but a team of physicists at the University of California, Irvine, have published a theory that there is a fifth one. If their theory is correct, it could change the way the universe is studies.
Four known forces determine behavior of all things in the universe, but a team of physicists at the University of California, Irvine, have published a theory that there is a fifth one. If their theory is correct, it could change the way the universe is studies.
NASA, ESA, The Hubble Heritage Team

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There are four laws of physics and nature govern everything in our world.

They are: gravity (which you may have heard of), electromagnetism (responsible for electricity and so much more), strong nuclear force that holds together nucleii, and weak nuclear force, which is nuclear decay.

Now, physicists say there may be one more. A team of physicists at the University of California, Irvine, published a theory that there may be a fifth force of nature, and they found about it almost by accident. A Martinez spoke to Tim Tait, a professor in the department of physics & astronomy, who is one of the authors of the study.

Interview highlights

This new theory came about from some data that some nuclear physicists in Hungary published last year. How did you come across it, and what made you decide to take a look at it?

What these experimental physicists in Hungary did is they produced an excited state of the beryllium nucleus. (A nucleus is a ball of protons and neutrons and...if you give it a bit of a nudge, you can actually get them moving around a little faster, and we call that an excited state of the nuclues). Eventually, it decays down into a lower energy state, the lowest one, which is called a ground state, and when it does that, it emits some kind of radiation. So what these authors did is they looked for a rare type of nuclear decay where you produce an electron and a positron, which is the anti-matter particle that corresponds to the electron. What they noticed was that the distribution of energy of the electrons that came out was very surprising for them. It had this feature that looks like a bump and this actually indicates a new particle, which could actually be a new force carrier (a particle that transmits a force). We actually found out about their paper by reading it online...and we realized that we actually could add something to the story by looking at what other experiments had told us about [what] the properties of this particle would have to be. Other experiments have also been looking for a fifth force—this search has been going on for decades—and they haven't found any until this most recent hint. So, by putting that info together (the hint that you have that there is something with the results that didn't find anything), you actually get this composite picture of what the properties of this force would be, and that's really what our contribution to this story is.

What does this mean for how physicists or scientists see the universe?

This is one result so far and now there are groups all over the world which are working to try to confirm it, and make sure that it's actually something that's there. We have no indications that there's anything wrong with our findings, but you always want to have an independent confirmation—since you're making an extraordinary claim, you need extraordinary evidence.

What it means for us physicists is that we have to go back to the standard model of particle physics, which describes electromagnetism and the weak and strong nuclear forces, and we've got to add this force into it. And, of course, there's all sorts of things we're going to learn when we do that because it's a big edifice with lots of moving parts that interact with each other, and so you can expect that adding this new force is going to change the way you think about even the parts of it you thought you already understood.

Do we even have to go back to our understanding of how the universe began?

Absolutely. This particle, if it has these properties, should be produced in the early universe and that means after the Big Bang, when the universe was a hot soup, it's part of the soup! So that could change the things we would expect to see today.

So how did this particle go all this time without being noticed?

That was actually part of our motivation. We saw this claim and we though, "well, shouldn't somebody else have seen that already?" Then, by looking into all the details of the experiment, you realize, "no, actually, there is a particle that would have escaped notice until now and been discovered by this experiment." Mostly though, the answer is because: first, it's short-range...if you're looking at macroscopic distances, it just doesn't act far enough for you to see it; and also because it's pretty weak. It's much weaker than the strong nuclear or the electromagnetic or even the weak nuclear force. It's still stronger than gravity though.

So all the brainiacs are excited—what does this mean for the average person?

I don't know yet, but I think that once you understand the basic ingredients of the universe, you put them together and you figure out what great things to build with them, but that's a job for someone else.

To hear the full interview, click the blue audio player above.