Nothing's the Matter With Antimatter, New Experiment Confirms (nytimes.com) 109
Many readers shared this report: Antimatter just lost a little more pizazz. Physicists know that for every fundamental particle in nature there is an antiparticle -- an evil twin of identical mass but endowed with equal and opposite characteristics like charge and spin. When these twins meet, they obliterate each other, releasing a flash of energy on contact. In science fiction, antiparticles provide the power for warp drives. Some physicists have speculated that antiparticles are being repelled by gravity or even traveling backward in time.
A new experiment at CERN, the European Center for Nuclear Research, brings some of that speculation back down to Earth. In a gravitational field, it turns out, antiparticles fall just like the rest of us. "The bottom line is that there's no free lunch, and we're not going to be able to levitate using antimatter," said Joel Fajans of the University of California, Berkeley. Dr. Fajans was part of an international team known as ALPHA, the Antihydrogen Laser Physics Apparatus collaboration, which is based at CERN and led by Jeffrey Hangst, a particle physicist at Aarhus University in Denmark.
Dr. Fajans and his colleagues assembled about 100 hundred anti-atoms of hydrogen and suspended them in a magnetic field. When the field was slowly ramped down, the anti-hydrogen atoms drifted down like maple leaves in October and at the same rate of downward acceleration, or g force, as regular atoms: about 32 feet per second per second. They published their result on Wednesday in the journal Nature. Few physicists were surprised by the result. According to Einstein's theory of general relativity, all forms of matter and energy respond equally to gravity.
A new experiment at CERN, the European Center for Nuclear Research, brings some of that speculation back down to Earth. In a gravitational field, it turns out, antiparticles fall just like the rest of us. "The bottom line is that there's no free lunch, and we're not going to be able to levitate using antimatter," said Joel Fajans of the University of California, Berkeley. Dr. Fajans was part of an international team known as ALPHA, the Antihydrogen Laser Physics Apparatus collaboration, which is based at CERN and led by Jeffrey Hangst, a particle physicist at Aarhus University in Denmark.
Dr. Fajans and his colleagues assembled about 100 hundred anti-atoms of hydrogen and suspended them in a magnetic field. When the field was slowly ramped down, the anti-hydrogen atoms drifted down like maple leaves in October and at the same rate of downward acceleration, or g force, as regular atoms: about 32 feet per second per second. They published their result on Wednesday in the journal Nature. Few physicists were surprised by the result. According to Einstein's theory of general relativity, all forms of matter and energy respond equally to gravity.
Since this is at CERN (Score:5, Insightful)
They probably fell at 9.8 metres per second per second.
They use metric in Europe
Re: (Score:1)
>9.8 metres per second per second.
Oof, not at today's exchange rate.
Re: (Score:2)
I'm used to "high rate of speed" from US police giving interviews or writing reports, but "same rate of ... acceleration" is new to me.
Re: (Score:3)
I'm used to "high rate of speed" from US police giving interviews or writing reports, but "same rate of ... acceleration" is new to me.
Obviously written by a jerk.
In other news: Gravity still isn't a force.
Re: Since this is at CERN (Score:3)
Re:Since this is at CERN (Score:5, Funny)
This is CERN, they probably changed their unit system so that c = 1. (Particle physicists like to do that.) That would make standard acceleration due to gravity g = 3.267E-8 [s^-1], which makes all the sense in the world.
Re: (Score:2)
Re: (Score:2)
An interesting equivalence (that isn't a priori necessarily so) is that the values of 'c' for
Re: (Score:3, Interesting)
They probably fell at 9.8 metres per second per second.
They use metric in Europe
We use both here in the USA. Europeans can only use one system.
Quite the meme that the USA doesn't use metric - but if that's what floats yer boat, have at it.
My garage shop is 100 percent metric, but I can make imperial parts without breaking a sweat.
Re: (Score:2)
In the UK we have both. It's pretty silly really, and somewhat divided by age groups.
For at least 40 years now, schools have been teaching metric, with Imperial units being just a brief "here's how to convert to SI". Still, a lot of newspapers use Fahrenheit instead of Celsius, so you get headlines about "mercury hitting 78 degrees" that half the country doesn't understand. On TV weather reports they mostly use metric.
For distances, short distances are in metres, but longer distances are in miles. Speed is
Re: (Score:2)
Re: (Score:2)
A liter is so close to a quart that it should make little difference. Especially since a liter is very slightly more than a quart. That would mean that, if she used exactly a quart, there would just be a very tiny bit left over to be wasted. I would say that her story sounds pretty dubious.
Re: (Score:2)
Yeah the UK is wild. People give you weights in stones. Not even wrong.
1 stone equals 6.35 kilograms. If people round it off in their heads, you can say 6.5.
I worked with an older British Woman for years. She always complained about metric. It changed how much product she bought. She wanted a quart of milk, exactly.
She was a bit dense. A liter is .946 quart. Given the margin of error in each, you're likely to get a liter in your quart, or a quart in your liter.
As much as its just a measurement system, its also more than that it influences packaging size and consumption.
Seems like a bottle that will hold a liter will hold a quart, and not many will miss or notice the .04 quarts in the bottle. Or 38 cc.
Yes, there are indeed dense p
Re: (Score:2)
A quarter of a US gallon, or of a UK gallon (I forget which is "Imperial")?
I remember that they're different, but since the last 5 years of my working life I was working 11 months of the year in metric, and only one month of the year with clients that wanted reporting in "oilfield units" (which they never define in advance), I can't remember what the conversion factor is. I know which book of reference tables I'd look it up in, but not which briefcase that book is in.
Re: (Score:2)
basically, our former imperial overlords, among their sins, give us gallons 1/6 smaller than the good ones they kept for themselves.
monsters, I tell you.
And now you know the *real* reason for the american revolution, the undersized pints of ale!
Re: (Score:2)
A quarter of a US gallon, or of a UK gallon (I forget which is "Imperial")?
I remember that they're different, but since the last 5 years of my working life I was working 11 months of the year in metric, and only one month of the year with clients that wanted reporting in "oilfield units" (which they never define in advance), I can't remember what the conversion factor is. I know which book of reference tables I'd look it up in, but not which briefcase that book is in.
It's a US Gallon.
Another oddity:
The Billion. Until after WW2, in England, a Billion was 10 to the 12th power - a million million. Other places, it was 10 to the 9th power, a thousand million. Or some combination of both. https://en.wikipedia.org/wiki/... [wikipedia.org]
And it surely isn't standardized even yet. https://en.wikipedia.org/wiki/... [wikipedia.org]
Billion doesn't even exist in some places. They use a "milliard". Some places use both. long and short scale, both terms. Note much of Europe uses long scale, so if you w
Re: (Score:2)
In the UK we have both. It's pretty silly really, and somewhat divided by age groups.
I mean sort of silly. But I consider the brouhaha, with people getting upset if someone uses an imperial measurement even more silly. I watch a lot of Youtube wood and metalworking, and sometimes the person making the vid gets browbeat for using an imperial measurement.
I'll decide one or the other is better when someone proves that something made with metric is more accurate than something made with Imperial.
Personally I have little intuitive grasp of Imperial measures, I always convert them to metric in my head. 1 inch is about 2.5cm, 1 foot is about 30cm, 1 yard is about 1m, 1 mile is about 2km.
It sounds to me kinda like you are grasping the imperial measures. Doing the conversion in your h
Re: (Score:2)
Other stuff is random, depends on the individual. Personal weight and height can be either system, I always use metric. TVs are randomly sized in inches or centimetres. Property is usually advertised in both, with metric first.
I think Finland is a pretty good example of a modern metric country, but I've never seen anything except inches on TV screen sizes here. They're not even actual inches, at least they weren't in the CRT days -- I remember 19'' CRTs having about 17'' of viewable area.
With today's huge flat screens in various aspect ratios, you'd think people were more interested in the width and height of the set in local units. But it's always the diagonal inches as it's always been done that way.
Re: (Score:2)
The point is you cling to the old ways like a kind of security blanket. Even though you claim "everyone in America can use both".
Is you "claim" even true? Your one example is just an anecdote anyway.
If I was lying - I'd be like you and post as an anonymous coward. Which sad to say - you are, even making up a strawman quote that I presumably said. Sorry, but I didn't say everyone in America can use both. Learn to understand the very big distinction between "we" and everybody. Switching between metric and imperial is no harder than switching between 10 mm and 11 mm. I do get it - for some people, it is not possible. That's because they aren't very adroit.
It's kind of funny though. Less capable people
Re: (Score:2)
Which is, of course, one of the strands in the "this amplifier goes up to 11" scene in Spinal Tap.
I've never looked, but I assume that amplifier companies sporadically go through phases of selling "Spinal Tap Conversion Kits", consisting of a bag of electronic garbage and a stick-on 0-11 label. And "unTapping" kits with similar contents, a bottle of flammable liquid,
Re: (Score:2)
Then I remember having to actually do exactly those explanations about how to use the same float+potentiometer sensor to record the volume in tanks of various shapes, including sloping side-tanks. Granted, my trainees weren't quite of Tufnell's ... state of being. But it could be really hard work!
Re: (Score:3)
32 ft/s/s is just easier because it is the same number as what water freezes at.
Re: (Score:2)
Re: (Score:2)
7.13 × 10^10 furlongs per fortnight per fortnight.
spin (Score:1)
Same spin, I'm pretty sure.
Re: (Score:2)
You're right. /some/ different particles (quantized and signed), or that a particle and its antiparticle necessarily reverse the signs of those things.
I can't tell if the original writer meant that charge and spin are quantifies which appear with equal magnitudes and opposite signs in
Re: (Score:2)
They mean chirality, although it's related to spin. The weak interaction only works between left handed fermions and right handed anti-fermions. Since we can only observe neutrinos through the weak interaction we've only ever observed left handed neutrinos and right handed anti-neutrinos, although there's no particular reason to think the opposites don't exist (and some reasons to think they do).
Re: (Score:2)
They mean chirality, although it's related to spin.
I think you mean that they mean "helicity". These are massive particles we're talking about.
Re: (Score:2)
That is precisely why I mean chirality. Chirality and helicity are equivalent for massless particles, but if you can go faster than they do you can find a frame of reference that flips the helicity. The chirality remains the same though.
Re: (Score:2)
Fine: helicity isn't conserved under a Lorentz boost, though it does commute with the Hamiltonian; chirality is /not/ a constant of the motion, though it's conserved under a Lorentz boost.
Wanna bet the writer meant neither of those things, and actually meant /spin/?
Re: (Score:2)
It doesn't matter what the writer meant. The phenomenon they're referring to is the charge-parity-time symmetry, in which an antimatter system is equivalent to a matter system under charge conjugation, parity transformation and time reversal. The parity transformation acts on the chirality, not the spin, and chirality is only equivalent to helicity and spin if you're a massless particle or nobody is playing relativity games.
dark matter? (Score:2)
They mean chirality, although it's related to spin. The weak interaction only works between left handed fermions and right handed anti-fermions. Since we can only observe neutrinos through the weak interaction we've only ever observed left handed neutrinos and right handed anti-neutrinos, although there's no particular reason to think the opposites don't exist (and some reasons to think they do).
If right-handed neutrinos and left-handed anti-neutrinos don't respond to the weak force, that means they only respond to gravity. Does that make them candidates for dark matter?
Re: (Score:2)
Re: (Score:2)
Not cold dark matter (cold here meaning the typical particle thermal speed is slow enough to be trapped in a galactic gravity well), since neutrinos would have had highly relativistic energies when they decoupled from other matter and the universe has not stretched nearly enough since then to make them non-relativistic yet.
Are you sure? Considering their low mass, neutrinos must have decoupled very early, and the expansion ratio since then could be very large.
Re: (Score:2)
Re: (Score:2)
Yes, sterile neutrinos generally, and right handed neutrinos in particular, are dark matter candidates. They'd have to be considerably heavier than the left handed variety to satisfy the cold or warm dark matter hypotheses, but that's kind of a feature because heavy right handed neutrinos can help explain the small but non-zero mass of the left handed ones.
It Depends (Score:3)
Same spin, I'm pretty sure.
That's definitely true for any charged fermion but not necessarily for neutrinos. If a neutrino is something called a Majorana fermion then an anti-neutrino is just a neutrino with a flipped spin. However, the one thing they definitely got wrong is that anti-particles are not evil.
Please make it stop (Score:3)
The ludicrous prose used in that summary makes my brain hurt. I feel dumber having read that.
Re: (Score:1)
Ludicrous prose is what powered Space Balls.
Re: (Score:2)
How so?
Imagine you have an electron traveling through 4 space (xyzt) with some velocity, and a gamma ray comes from the future and whacks into it hard enough to change its speed along the t axis from c to minus c, so the electron goes flying off on a new course traveling backwards in time.
Weird, huh? Well what does a reverse time traveling electron look like from a normal traveller. Well it repels itself from elections as it goes backwards, so going forwards or attracts itself to them. So looking at it goin
Re: Please make it stop (Score:1)
no, that time reversal was postulated by Feynman in 1940s but only ever used as just a convient math trick with way too many contradictions in reality to be true, the time arrow is direction of entropy increase and is identical for antimatter for example.
Phycists don't believe it.
Re: (Score:2)
That's kind of the point of this experiment, is it not?
Antimatter falls down in a gravity well (Score:5, Informative)
The ludicrous prose used in that summary makes my brain hurt. I feel dumber having read that.
The question was whether antimatter experiences anti-gravity.
This was a long standing question in physics. Einstein's general relativity suggests that all matter would experience gravity (and not anti-gravity) because gravity is the warping of space time, but people still wanted to do the experiment to be sure.
The experiment is very difficult to do. Anti-electrons are lightweight and subject to the faintest of electric fields (and gravity is relatively weak), so the experiments were like measuring a cork on the ocean during a tornado (actual phrase used in physics class when we discussed this).
Anti-atoms would be electrically neutral and easier to measure, but making these is difficult because man-made antimatter particles have tremendous kinetic energy - you need to cool them/slow them down before they will pair up and form anti-atoms.
It appears that people at CERN were finally able to accomplish this (anti-atoms), and were thus able to measure their gravitational attraction directly.
A long standing question was answered, by experimental method.
Re: (Score:1)
What would have been the alternative? If antimatter was repelled by earth, it would also be repelled by the sun, by the center of our galaxy, etc. So which way would it end up going? The very idea of relativity would be instantly refuted if you could reverse every gravitational effect in the universe. Motion would end up being absolute after all. That would be a pretty unlikely outcome.
Re: (Score:2)
It seems like this is how science communication works now, they have to explain things like marketing copy. It's like Mr. DNA but 100x worse.
Not even sci-fi made them antigravity (Score:4, Insightful)
In sci-fi all warping or anti-gravity things were done using massive amounts of power to create these fields or space time warping effects. Anti-matter has always been a sci-fi source of massive amounts of energy and that's about it afaik, and like all energy, for explosions and what not.
Nasa estimated that it might be possible to bend space time with enough energy too.
Completely expected [Re:Not even sci-fi made t...] (Score:2)
Yes, this result is completely expected. We already knew what the result was going to be, because the energy required to create a proton/antiproton pair is independent of where it is in the gravitational field (if antiprotons fell upward instead of down, then putting them in a gravitational field would give them positive potential energy, and hence it would cost more energy to make them).
But it's good somebody did the experiment. If the result were different, then everything we thought we knew was wrong, an
Re: (Score:2)
Also, photons are their own anti-particles and bend toward mass.
If anti-matter was repelled instead of attracted, it would mean General Relativity is fundamentally wrong.
Re: (Score:2)
Re: (Score:2)
Yeah I think the experiment is important, I just mock the sensationalistic headlines like it's big news. "Anti-matters math checks out!" Okay, what's that mean?! "Nothing!".
Hmm..okay. I mean thanks for sharing I suppose but articles just confirm a theory that doesn't actually change anything, like nothing new can be done with this knowledge. It's good that they tested it, as if we had different results that would be very essential, but it's like if someone said "Math shows that walking generally requires pu
Re: (Score:2)
There's a known particle that does that: the Trumpion.
On a more respectable note, doesn't this experiment imply that gravity is not a force comparable to the other 3? Otherwise, the anti-particles would have fell up. Gravity violates symmetry.
Re: (Score:1)
> It acts differently than the other forces. So not sure what you are getting at.
You answered your own question.
Re: Not even sci-fi made them antigravity (Score:2)
Gravity is not a force. Itâ(TM)s just space time being curved.
Re: (Score:3)
Re: (Score:1)
We don't know that. We know it "acts like" space/time being curved, but that may merely be our best matching model of the moment.
Re: (Score:2)
Gravity violates symmetry.
Which kind of symmetry does gravity violate? If you mean that all energetic/massive things move the same in response to gravity, that's a symmetry which is /not/ violated.
If you mean there should be a mapping between (say) electric charge and gravitational charge, and thus a form of mass which feels a force /away/ from a "conventional" mass, well, I'm sorry.
Charge and parity both lead to breaking of symmetry under the weak force; the resolution of this in the form of CPT invariance necessarily leads
Re: (Score:2)
In sci-fi all warping or anti-gravity things were done using massive amounts of power to create these fields or space time warping effects. Anti-matter has always been a sci-fi source of massive amounts of energy and that's about it afaik, and like all energy, for explosions and what not.
Nasa estimated that it might be possible to bend space time with enough energy too.
Maxim 24 [fandom.com] Any sufficiently advanced technology is indistinguishable from a big gun.
Einstein not NASA (Score:4, Informative)
Nasa estimated that it might be possible to bend space time with enough energy too.
Nice try but Einstein showed that happens in 1915 when he published General Relativity and Eddington first showed that he was right in 1919 by measuring the deflection of light from a distant star close to the sun in the sky during a total solar eclipse. NASA did not exist at all until almost 40 years later in 1958.
Re: (Score:2)
That's due to mass, not energy.
Protip: e=mc^2
Re: (Score:2)
No, Einstein.
Mass IS energy. The mass of the sun is already energy.
Mass and Energy are Equivalent (Score:3)
That's due to mass, not energy.
Happily, Einstein also showed that mass and energy are equivalent. With the discovery of the Higgs, we even know where the energy that makes up the mass of fundamental particles comes from.
Re: (Score:2)
The mass didn't flatten the cities, only when that mass was changed into energy did that happen.
You can think of mass as just stationary energy so really it was just releasing the energy bound up as mass not changing it into energy.
The detailed mechanism shows this even more clearly since the energy comes from increasing the nuclear binding energy per nucleon of a nucleus. This removes energy from the nucleus which results in a reduction in mass because mass is literally just the energy bound up in the nucleus from the nucleons binding to each other, the quarks binding together to form the nucleon
I liked this story better last year. (Score:2)
Re:I liked this story better last year. (Score:5, Informative)
You'll note that at the end of that story, they mention that dropping of antimatter in Earth's gravitational field had yet to be done; today's report is the results of just that experiment.
Nice way to confuse of plebs. (Score:1)
Re: (Score:3, Insightful)
Testing CP Violation (Score:5, Informative)
Nobody's ever had a large enough amount of it to test whether its mechanical properties (like maleability and tensile strength) are what would be expected for the corresponding normal matter.
True but we have tested the atomic spectrum of anti-hydrogen so we know that the positron energy levels are identical to the electron levels in normal hydrogen. Given that the mechanical and chemical properties of materials all stem from electron interactions between atoms if those are identical then all the bulk properties that depend on them should be identical too.
Is anti-oxygen or anti-carbon even a physical possibility?
Yes, but there is very little interest in making them since it doesn't really test anything because we can't yet do detailed calculations of nuclear structure from first principles - QCD is non-perturbative which makes the calculations impossibly hard. Studying anti-atomic spectra is important because we can do both theory and experiment with great precision so it is a good way to see whether the electromagnetic force differs between matter and antimatter (technically whether it is CP violating). This is important since the universe is full of matter without any antimatter so there must be some difference between them and the only difference we have seen so far in quarks (plus a hint in neutrinos) is not enough to explain the difference we see.
Re: Nice way to confuse of plebs. (Score:4, Funny)
To be clear, you absolutely can do the experiments you described. What happens is you get a lot of energy very fast.
Re: (Score:1)
Too many idiots on slashdot now....
Re: (Score:3)
Where'd you get the idea antimatter has yet to be "proven"? Your body generates a few thousand positrons a day through decay of radioactive potassium. If you ever go for a PET scan, the P stands for "positron."
Re: (Score:3)
Nope, anti-electrons are quite well known and are used in PET scanners in hospitals around the world. Their mass is the same as an electron, and when the two meet they annihilate to produce two 511 keV gamma rays. It is these gamma rays which are detected by a PET scanner.
Anti-protons are much harder to make because they require over a thousand times more energy than an anti-electron. So much energy that there is no prospect of producing an isotope which emits anti-protons. Instead they are produced at CERN
Re: (Score:3)
Antimatter has been proven to exist and measured in particle accelerators for decades now. Scientists have repeatedly created and detected various antimatter particles like positrons and anti-protons. Particle/anti-particle pairs have been declared to have the same mass. This experiment demonstrates that.
Antimatter was first experimentally confirmed in 1932 by physicist Carl David Anderson.
Re: Nice way to confuse of plebs. (Score:2)
Antimatter exists, first detected in the 1930s and mankind has been making it for decades. Your science education is lacking.
Fantastic (Score:1)
Re: (Score:1)
If physics has a sense of humor, it will make anti-gravity kick in slowly, so that the bombs reverse and make their way back up to the jet.
Re: (Score:2)
... which will now be in a different place, since it generates lift by the differential motion of the air and it's wings.
TTBOMK, nobody has seriously proposed a helicopter-launched nuclear bomb. Yet.
Re: (Score:1)
> which will now be in a different place
Only in an approximately different place. An anti-matter bomb only needs "kind of close".
Warm Tea and a Big Bang (Score:3)
Tachyons? (Score:1)
Physicists know that for every fundamental particle in nature there is an antiparticle -- an evil twin of identical mass but endowed with equal and opposite characteristics
Did someone finally prove the tachyon exists? I missed that.
Re: (Score:2)
I don't think they have yet.
And if they're charged tachyons, wouldn't they lose energy by emitting Cherenkov radiation, and therefore speed up to infinite speed?
Tachyons = Time Travel (Score:2)
Re: (Score:1)
Why 60? Why not? It could be 100 decimal minutes. (See e.g. "decimal clocks" ;-)
You can divide 60 by 30, 20, 15, 12, 10, 4, 3, 2.
Now try that with 100.
Re: (Score:3)
Re: (Score:2)
Cough. [wikipedia.org]
Negative charge/spin don't give negative mass. (Score:3)
Re: (Score:2)
The summary was pretty clear on that, and there's an upthread comment that explains it reasonably well.
The plain and simple fact is that we had not, until this experiment, actually observed anti-matter's interaction with gravity. Because electrical and magnetic fields are so much stronger than gravity, we needed neutral bits of anti-matter to test gravity, and the easiest way to do that (which is by no means easy) is to create a bunch of anti-hydrogen (a positron bound to an anti-proton) suspended in an ab
Re: (Score:2)
Re: (Score:2)
That's not what I asked. Investigating the question is fine in itself, but why was that particular question considered to have a decent chance at yielding meaningful new information? What was the ambiguity that needed clarifying?
There was enough interest in the right people who decided to spend their time on it. There is a lot of widespread interest in how gravity really works and the limits of the General Relativity model of it. I doubt this is sensitive enough to probe into any small deviations from the expected result, but just demonstrating that anti-matter wasn't super different is useful, and constrains anyone working in alternative models to the generally accepted ones.
We still have no real idea why inertial mass and gravita
Even photons 'fall' so why wouldn't antimatter? (Score:1)
I'm not a physicist, but given that photons respond to gravity, it would be really, incredibly strange if anti-matter behaved differently, seeing as how photons are made from matter and anti-matter collisions.
Of course, it was still worth doing the experiment. From what I understand, physicists are always looking for surprises, and how else are you going to find them?
Does antimatter v.bis (Score:2)
There is a slightly different variant of the same question does the gravitational field created by the anti-matter oppose or add to the gravitational field of normal matter.
To put it another way imagine there were two spheres (one made of matter, the other antimatter) of equal mass and size separated by some distance in space and initially placed at rest to each other.
Would they mutually attract each other or would the gravity wells between each sphere cancel out keeping them at rest? That would be one hel
Re: (Score:1)
Re: (Score:2)
Actually ball-parking the numbers in my head ... for planetary (Earth) masses, of matter and anti-matter, self-gravitating together ... it would be a supernova-scale event. So in a reasonable size galaxy (Magellanic cloud, upwards) you're quite unlikely to be damaged by the event.
Well duh (Score:2)
Of course we won't use them to levitate, that's just sci-fi nonsense.
We'll use them to power our FTL warp drive.
Dark AntiMatter? (Score:1)
Re: (Score:2)
Antimatter is matter. That's all that matters.
NYTimes confused about physical properties (Score:2)