Cosmologists Show Negative Mass Could Exist In Our Universe 214
KentuckyFC (1144503) writes The idea of negative mass has fascinated scientists since it was first used in the 16th century to explain why metals gain weight when they are oxidized. Since then, theoretical physicists have shown how it could be used to create exotic objects such as wormholes and the Alcubierre warp drive. But cosmologists' attempts to include negative matter in any reasonable model of the cosmos have always run into trouble because negative mass violates the energy conditions required to make realistic universes with Einstein's theory of general relativity. Now a pair of cosmologists have found a way around this. By treating negative mass as a perfect fluid rather than a solid point-like object, they've shown that negative mass does not violate the energy conditions as had been thought, and so it must be allowed in our universe. That has important consequences. If positive and negative mass particles were created in the early universe, they would form a kind of plasma that absorbs gravitational waves. Having built a number of gravitational wave observatories that have to see a single gravitational wave, astronomers might soon need to explain the absence of observations. Negative mass would then come in extremely handy.
"Absence of observations" (Score:2)
The summary makes mention that we haven't noted any substantial signs of this material, but how is that any different from, say, antimatter, which we know can exist?
We've observed and created antiparticles (Score:2, Informative)
The summary makes mention that we haven't noted any substantial signs of this material, but how is that any different from, say, antimatter, which we know can exist?
Not too long ago, I think we even created an anti-hydrogen atom.
Negative mass? Not so much (yet).
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Not only have we created them, we have small stores at CERN and a few other facilities for experimentation on.
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Did not know that. What kinds of medical imaging?
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PET scan
http://en.wikipedia.org/wiki/P... [wikipedia.org]
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I love living in the sci-fi world the past predicted. Well, not the parts Orwell predicted, but you can't have everything.
Negative mass- not antimatter, but odd (Score:5, Informative)
Negative mass is very diferent from antimatter. Antimatter is opposite to normal matter in charge and quantum numbers (such as baryon number, etc.), but still has positive mass.
Negative mass reacts oppositely to both gravity and intertia. Oddly, that means that negative mass still falls down in a gravitational field: The gravitational force is opposite, but negative mass responds negatively to force (a=F/m, where both F and m are negative). So negative mass particles repel each other gravitationally, but are attracted to positive mass objects.
This has peculiar consequences. One consequence is that, for objects of negative mass, gravity and electrostatic charge switch. For normal mass objects, gravity is attractive, but like electrical charges repel. For negative matter, gravity is repulsive, but like electrical charges attract.
I wrote about this [nasa.gov] once, in the AIAA Journal of Propulsion and Power-- not a journal that physicists usually read, I'm afraid. If you have access to AIAA online, it's here: http://arc.aiaa.org/doi/pdf/10... [aiaa.org]
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So, I will happily demonstrate my complete lack of understanding on this topic ...
Is this similar to, unrelated to, part of, dissimilar, orthogonal, integral, or in any way linked to Dark Matter?
Because I (and probably most of us) don't understand that either.
Re:Negative mass- not antimatter, but odd (Score:5, Funny)
Almost, but not quite, entirely unlike Dark Matter.
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LOL, so you don't know either then?
Re:Negative mass- not antimatter, but odd (Score:4, Funny)
Hell, I don't even know what we're talking about.
Dark energy is negative (Score:3)
Is this similar to, unrelated to, part of, dissimilar, orthogonal, integral, or in any way linked to Dark Matter?
It's unrelated to dark matter (which has positive mass- that's how we know it's there), but dark energy is gravitationally negative (it causes expansion to accelerate: it's gravitationally repulsive)
Because I (and probably most of us) don't understand that either.
You're in good company! If you did understand it, you could publish, and you should be getting a phone call from Stockholm soon.
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Wait ... dark matter and dark energy are separate things now? Are they related? Or totally separate things?
Honestly, are you guys just fucking with us? ;-)
Oh, good, I'm not supposed t
Yes, they're separate (Score:4, Informative)
Dark matter conerns the "missing" (i.e. never observed directly) mass in the universe, which has despite its "invisibility" been observed indirectly; for example look up Bullet Cluster on Wikipedia.
Dark energy concerns what it is that is causing the expansion of space-time (and consequently) the universe itself.
Re:Dark energy is negative (Score:5, Informative)
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I thought the anomalous galactic rotational curve had been almost entirely explained a year or two ago by repeating the analysis using the far more computationally expensive Relativity theory rather than the known-flawed Newtonian theory of gravity. There's still the gravitational lensing anomalies, bullet cluster, etc. supporting the existence of DM, but the while galactic rotation was the impetus for postulating it's existence, it's no longer a strong supporting argument.
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Thanks for the update, guess I'll need to keep an ear out for future developments.
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My way of remembering it is this: Dark matter is why large structures (galaxies) don't fly apart. Dark energy is why even larger structures (the universe) does.
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The question is what would happen in an encounter of 2 objects with symmetrical masses?
The speculation is about negative mass and antimatter... What if, somehow, negative mass was more attracted to antimatter? Could that explain why there is so little antimatter around?
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Negative mass reacts oppositely to both gravity and intertia. Oddly, that means that negative mass still falls down in a gravitational field: The gravitational force is opposite, but negative mass responds negatively to force (a=F/m, where both F and m are negative). So negative mass particles repel each other gravitationally, but are attracted to positive mass objects.
Aw dammit, I was hoping we could build antigravity vehicles from this stuff...or at least some negative mass body panels to lighten up my car :-(
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If it exists, we can do something so much better - we can build Alcubiere Drives - that is, the real version of what Star Trek called "Warp Drives".
(This reference is not accidental - Star Trek inspired Alcubiere's research as he himself pointed out in an e-mail to Shatner - he wanted to test if Star Trek's loophole was really possible, and he found out it is at least theoretically possible, but only if negative mass exists).
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Negative mass is very diferent from antimatter. Antimatter is opposite to normal matter in charge and quantum numbers (such as baryon number, etc.), but still has positive mass.
Negative mass reacts oppositely to both gravity and intertia. Oddly, that means that negative mass still falls down in a gravitational field: The gravitational force is opposite, but negative mass responds negatively to force (a=F/m, where both F and m are negative). So negative mass particles repel each other gravitationally, but are attracted to positive mass objects.
Trying my best to ignore my intuition, which is heavily biased toward "all mass is positive":
A negative mass would fall down in a gravitational field (generated by a positive mass) -- it would experience a force directed away from the positive mass, and it would respond to that force by moving toward the positive mass.
However, the negative mass would repel the positive mass gravitationally -- effectively, exert a force directed away from itself -- correct?
It seems to me that if you had two equal but opposit
Negative mass is weird (Score:5, Informative)
What am I missing?
Nothing. Negative mass is weird.
What you're pointing out -- that a positive mass and a negative mass would chase each other-- was pointed out in 1957 in Bondi's paper about negative mass, "Negative Mass in General Relativity". Rev. Mod. Phys. 29 (3). Robert Forward, in 1990, then extended that analysis even further and pointed out that negative mass is even weirder than that.
A negative mass chasing a positive mass accelerates forever... but it doesn't violate conservation of energy, because the faster a negative mass moves, the more negative the kinetic energy, so the positive kinetic energy and the negative kinetic energy cancel out, leaving energy conserved.
There are weirder things than that, too.
If you think this is so weird that bulk negative mass can't exist... well, that's what Einstein thought (the "positive energy condition").
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Okay, as long as I've got you on the line... :)
What's supposed to happen when negative and positive mass collide?
If I throw a tennis ball at a wall, it bounces off (and the wall recoils imperceptibly). If I throw a negative tennis ball at a wall -- or throw it away, causing it to move toward the wall, whatever -- what happens when it hits? It seems like it would try to "recoil" in the same direction it was traveling, maybe even giving the wall a "tug" instead of a "push" when it hit. But it can't move forwa
Re:Negative mass is weird (Score:5, Informative)
Okay, as long as I've got you on the line... :)
What's supposed to happen when negative and positive mass collide?
If I throw a tennis ball at a wall, it bounces off (and the wall recoils imperceptibly). If I throw a negative tennis ball at a wall -- or throw it away, causing it to move toward the wall, whatever -- what happens when it hits? It seems like it would try to "recoil" in the same direction it was traveling, maybe even giving the wall a "tug" instead of a "push" when it hit. \
Well, I already said negative matter is weird.
Robert Forward proposed that when positive matter and negative matter touch, they cancel each other out, and vanish:
(+) + (-) --> 0 (vacuum)
The mass cancels, and you're left with nothing there.
Unfortunately, we know that this can't happen, because if it did, then the opposite reaction could occur:
0 --> (+) + (-)
--vacuum spontaneously generating pairs of positive and negative mass. If this could happen, it would happen, everywhere, all the time. But it doesn't. So there are rules (presumably conservation laws) forbidding this from occurring.
But it can't move forward, because presumably negative and positive matter can't simply interpenetrate -- or can they?
Of course they can interpenetrate. The reason that you can't walk through a brick wall is because of Pauli exclusion [physlink.com]: the electrons in your body can't occupy the same place (the same quantum state) as the electrons in the wall. But, whatever negative matter is, it's not electrons (nor any of the other particles that make up "solid" matter). So, yes, it would pass right through ordinary matter.
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Out of interest, if there were pair creation events of involving particles of negative mass/gravity how would we detect them?
I'm not being critical, I'm curious - how would a particle accelerator, or a bubble chamber or whatever, look different with a negative mass particle?
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Out of interest, if there were pair creation events of involving particles of negative mass/gravity how would we detect them?
You're asking a lot, since we don't really know what the property of the particles are. A negative mass particle would curve in electric and magnetic fields (the usual way to determine what a particle is) just like a positive mass particle of the opposite charge. However, since negative mass particles also have negative kinetic energy, conservation of energy means that the remaining particles will have more energy coming out of the collision than they did going into it.
I'm not being critical, I'm curious - how would a particle accelerator, or a bubble chamber or whatever, look different with a negative mass particle?
Positive mass particles emit positiv
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Ah, the
Pauli exclusion
principle. IANA physicist, but I've never been happy with this here thingy. As the article states, "Wolfgang Pauli gave physics his exclusion principle as a way to explain the arrangement of electrons in an atom. His hypothesis was that only one electron can occupy a give quantum state." This is a principle without an explanation. It's one of those physics things that you have to take on faith, and because nothing works without it. AFAIK there's never been any real explanation of _why_ this pr
Pauli Exclusion [Re:Negative mass is weird] (Score:3)
Ah, the
Pauli exclusion
principle. IANA physicist, but I've never been happy with this here thingy.
Fortunately, your happiness is not relevant to whether physics works.
...
Oh, BTW - this is just one of many examples where science does, in fact, depend on pure faith.
No, this is one of the many examples where science depends on pure observation. The Pauli exclusion principle was first arrived at from observations, and only somewhat later was the theoretical basis-- the spin-statistics theorem [utexas.edu]-- worked out.
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"all mass is positive":
Well, in truth some mass is just not quite _sure_, but is willing to go along with the consensus.
And some mass is on a downer, and just not the type to be 'up' all the time.
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You should do an ama.
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>Negative mass reacts oppositely to both gravity and intertia.
Well, that's one hypothesis. But as I recall there are several hypothesis for each of the three possible interpretations of "negative mass", and none of them have any supporting evidence for actually existing.
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Would an opposite reaction to inertia mean that an object becomes easier to accelerate the more massive it becomes?
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No, assuming you mean negative inertial mass it would probably just accelerate in the opposite direction. You push on it, it moves towards you instead of away, and you generate energy instead of expending it.
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It means that if you have 2 objects, one of negative mass and one of normal mass (and nothing else around) The negative mass object will fall toward the normal one, and the normal one will be repelled by the negative one. The negative mass chases the normal mass and accelerates.
As the speed increases, the acceleration increases (once you get to a significant fraction of the speed of light)
It makes a good 'space drive'.
I wish I had patented the idea back in 1976 when I first thought of it when I was taking
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The sum of energy being zero does not mean either particular component is zero. +apple can have scads of energy as long as -apple has negative scads, and transferring some +apple's energy to the wall does not change the total energy in the system. It does probably mean that -apple will catch up to and pass +apple, at which point the acceleration will be in the other direction but the exact behavior depends on relative speeds because that affects distances. (I'm ignoring the effect of gravitational interacti
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But an anti-hydrogen atom still has mass.
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Dark Matter certainly exists - as certain as anything in cosmology. We know a few things about it: it reacts normally to gravity, but it doesn't interact with light or electrons in any way (these things are true of neutrons as well, of course). Further, it has no analog to EM interaction that could produce friction in some other way - we know this because it doesn't clump like normal matter.
How do we know this? There were many theories for the galactic rotation rate anomaly, but only the WIMP (dark matt
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Of course it does exist. It was discovered by Dr. Cavor and is sold as Cavorite(TM).
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The summary makes mention that we haven't noted any substantial signs of this material
They're just pointing out that it CAN exist, like unicorns and the Loch Ness monster.
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Yes, but the point was that we don't really see much sign of it in the stars above, not that we've never observed it at all.
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Come on man, I said "much". I'm aware of the history here.
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It's not about sight. It's always about measurement.
Finally... (Score:2)
A goal for all those zero sized models and weight loss fanatics to aim for!
This kind of thing confuses me (Score:2)
This kind of subject always leads to a cascade of stupid questions in my head that I can't answer, leaving me feeling even dumber than usual. Does negative mass necessarily imply negative weight? What about momentum and kinetic energy? If a lump of matter with negative mass hit something, would it actually absorb energy from it rather than imparting energy to it? Would a negative-mass planet have an anti-gravity field? Is it even meaningful to talk about matter with negative mass, or is some physicist going
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You forgot the most important question:
Can I use this to make a flying car and/or hoverboard?
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Given that negative mass atoms repel each other, a negative mass planet would never form. Even if one did form, it would disintegrate rather violently within seconds. Probably be fun too watch.
So, negative mass atoms could only form thin gas clouds.
Re:This kind of thing confuses me (Score:5, Interesting)
An excellent question, and as yet we don't have an answer.
There are actually two apparently unrelated phenomena we call mass - inertia and "gravitational charge", and last I heard we don't even have any substantial hypotheses as to why the two always seem to appear in the same ratio. The properties of a "negative mass object" would vary wildly depending on whether one or the other, or both properties were negative.
Negative gravitational mass only would mean you have an object that behaves as normal, but would presumably be repelled from normal gravitational matter (and then there's the question of how it would react to other negative matter - a naive hypothesis would be mutual attraction - rather like electrostatics except that like charges attract and dislike charges repel.
Negative inertial mass would likely mean that acceleration would be in the opposite direction of applied forces - push on a chunk and it would move towards you (basis for a cool "reactionless" drive?). This would also be repelled from normal mass, but for a different reason - gravitational forces would pull on it just like normal matter, but the resulting acceleration would be in the opposite direction.
If both are negative then you get stuff that acts like normal matter so long as only gravity is affecting it - gravitational forces would repel it from normal matter, but since the inertial mass is negative the resultant acceleration would be toward the gravitational source. All other forces would still result in backwards acceleration.
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Glad I came back to look for later replies, thanks for that.
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FWIW, I believe that General Relativity is based on the idea that those aren't really two distinct things, but rather the two "ideas" of what mass is are two different ways of talking about the same basic reality. If you want to really consider them as separate things that just happen to be equal, then I think you need to replace General Relativity with something else...and there don't appear to be any good candidates.
Why do we keep trying, then? (Score:2)
If they must see that same single gravitational wave over and over again, why do we need to keep building more of them? Why don't we build some to see OTHER gravitational waves?
OMG! A (possibly) testable theory! (Score:5, Interesting)
Before I read the article, I'd have been predisposed to agree with the poster who called this "The crackpot cosmology theory Du Jour". However the article does note that not only does negative matter possibly explain the current lack of detection of gravitation waves but (presumably unlike many other phenomena) predicts that if there is negative matter, we WOULD be able to detect gravitational waves but only above a certain frequency:
"the evidence that could back it up would be the discovery of the threshold frequency above which the waves do propagate"
If anyone who can read and understand the actual paper could tell us non-cosmologists when our improving technology might be able to detect gravitational waves above the cut-off frequency I would appreciate it. I mean is it technology that is (very roughly) 10 years away, 25 years, a century or basically only when we have god-like powers. I seem to remember that NASA was going to launch a space based interferometer with "arms" (free floating platforms) in a triangle 5 million km on a side. Would that be able to detect them? The whole point now isn't just to prove the existence of gravity waves but also negative matter (and the possibility of warp drives, yay!).
Actually, since (if I am reading the article correctly) they are looking for "higher frequencies", doesn't that mean the detectors should be smaller? ("arm" length shorter?) Shouldn't they be increasing the sensitivity instead? Or is the sensitivity increased by making the detector larger? I'm so confused!
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Dark energy (Score:2)
Wouldn't negative gravity obviate the need for dark energy?
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The 'dark' in 'Dark energy', means we don't know what it is.
It wouldn't obviate the need for dark energy, it would be dark energy.
COme on (Score:2)
find a way to make them in the lab. I want my anti-grav car.
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Negative mass could exist in the universe (Score:2)
But there probably is less than a pound of it!
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wrong
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Re:The crackpot cosmology "theory" Du Jour (Score:5, Interesting)
As I understood it with my very limited knowledge of physics, there are perceivable phenomena that did not quite make sense because it was an either/or situation.
In that case, Occam's Razor makes way for Sherlock Holmes' "Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth."
A model that allows for more of the perceived phenomena than previous models must be taken under more scrutiny.
Forget the banana! (Score:2)
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Forget the banana!
= my new catch-phrase, perhaps replacing "We're all gonna die!" - thanks! ;D
Re:The crackpot cosmology "theory" Du Jour (Score:5, Insightful)
As we better understand the universe, we find gaps between reality and our understanding. We then try to extend our understanding to better match reality, and that means filling in those gaps. Sometimes it takes many tries to fill in a gap, or at least make it smaller.
Negative mass is one of those attempts, and it's worth noting that they aren't clinging to the concept, they're simply suggesting that it's one possibility that can be tested. In other words, they actually are using Occam's Razor. In this realm, nothing is simple, which makes the Razor harder to use.
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Math doesn't take as much funding, but with enough math, you can hope to get a mite of funding.
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that we know to be true
... given the existing theoretical model
we must always keep in mind that, just as Newton's model turned out to be incomplete, the present model may - nay is - incomplete. Or incorrect. Or ??
Occam and White (Score:3)
What ever happened to Occam's Razor?
It competes with the totalitarian principle, "everything that is not forbidden is compulsory."
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It is important to note that this does NOT mean that negative mass exists, only that, so far as we know, it could exist. All it means is that it is now another po
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You use it to make concrete predictions about future observations. There might be several such "negative matter" theories, each with a different model and each making different predictions. Much like we had WIMPs and MACHOs for dark matter.
Then you wait for new observations that fit the predictions (or, more likely, don't), and importantly that don't fit the null hypothesis. Something new, that accepted theory doesn't explain, but some hypothesis specifically and accurately predicted.
That's the scientifi
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IIUC, it's not speculative at all. It's a work of math saying that this particular math is consistent with General Relativity. There are lots of things that are consistent with General Relativity, and most of them don't have any evidence of existing. There isn't much that appears inconsistent with General Relativity that DOES appear to exist.
Think of it as a Venn Diagram. Mark one circle "consistent with General Relativity". Mark another circle inconsistent with General Relativity. Now take a couple
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Anyone else sick of these fantasies?
What ever happened to Occam's Razor?
Occam's Razor doesn't apply here. They are not trying to explain something. They are showing that something is possible. Just because negative mass is possible, doesn't mean it really exists.
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In a way it does. They are offering that since the simplest answer was incomplete there's at least one slightly more complicated way things might work. You see, the simplest explanation isn't the thing. The simplest explanation that actually explains things is.
What happened to Occam's razor. (Score:3)
It was used by William of Ockham in the late middle ages to argue against the species theory of perception -- the idea that everything you can see constantly emanate images of themselves in every direction. It states (in scholastic Latin) "Do not multiply entities beyond necessity."
It was then stripped of its context somewhere halfway through the previous century, became a rallying cry of pretty much every self-proclaimed skeptic, and erroneously believed to say "the simplest explanation is usually right"
Th
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Excuse me, 14th century.
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Even worse, he never actually said that!
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It's alive and well. As strange as some of the ideas are, they DO represent the most simple explanation we have for the given observations.
Consider, the whole idea of epicycles was entirely appropriate until eliptical orbist were mathematically shown to be possible and that they matched observation. Then and only then, Occam's Razor dictated that we adopt the theory that planets were in elliptical orbits.
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Actually no - epicycles were an attempt to explain the motion of the planets while keeping Earth at the center of the universe, and have nothing to do with ellipses. The planetary orbits all have such low eccentricity that they are almost perfect circles anyway - IIRC as seen from Earth you never get more than a degree or so of discrepancy in planetary positions if you assume circular orbits instead of elliptical, and most planets don't vary even that much. The largest discrepancies are the result of plane
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Actually yes. Copernicus discarded geocentricism and found that the heliocentric model greatly simplified things, but he retained circular orbits with the planets moving at uniform speeds which still required epicycles to match observation. (in fact, it would have required an infinite number of epicycles to exactly match observation).
Kepler took the next step with elliptical orbits and so was able to predict planetary motion with unprecedented accuracy.
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Man who doesn't understand the science, the math, or the data, calls theory crackpot. News at 11.
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Definition: "Crackpot: disagrees with me." :D
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Anyone else sick of these fantasies? What ever happened to Occam's Razor?
Occam's Razor states that your personal theory that isn't testable is automatically false and invalid. The theory in the article that is testable may be right or wrong but we won't know until testing it.
Since your "faith" that everything you dislike must be wrong is automatically ruled out as an option, could you please stop posting useless tripe? The world would be a better place once people like you get your fingers out of science.
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Occam's Razor states that your personal theory that isn't testable is automatically false and invalid. The theory in the article that is testable may be right or wrong but we won't know until testing it.
Actually, no. Occam's Razor (as others have noted) is more or less about choosing the simplest theory that fits the facts. Falsifiability is about whether a theory is testable or not.
I'll just add this irrelevant point: any theory that concerns the Universe as a whole, viewed as a system from outside, is inherently unfalsifiable, even though it may be true. I can say, "the Universe is blue, viewed from outside", and there is no way to prove that, so far.
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actual evidence that warp drive cannot be created and it is called the Fermi Paradox.
- that's not evidence. That's a question, for which the answer has not been determined. It's not even certain that the assertion upon which the question is based, "we have not heard from them", is true.
F'ing balloons, how do they float? (Score:2)
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What is the sound of one balloon inflating?
Oh wait, I forgot, this isn't Jeopardy!.
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You're confusing negative mass with antimatter - antimatter reacts violently with normal matter due to the nature of the quark interactions, but there's no reason to assume negative mass would do the same.
If it did though - I imagine they'd simply wink out of existence: a chunk of normal mass (antimatter included) represents mc^2 mass-energy, a chunk of negative mass presumably has the same magnitude of negative mass-energy: mc^2 + (-m)c^2 = 0.
For the rest of your post, please be aware that there are two a
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mc^2 + (-m)c^2 = 0
OK, here I go on a wild toot. What if c^2 is negative? I.e. the "speed of light" is a complex number, or a pair of numbers, one of which is real and the other is imaginary? Then we might have c and c^2, and we can define the imaginary C=ic and C^2 = i^2c^2. This is different than the topic of negative mass, of course. I think I just boggled myself.
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Wild toot is right - how exactly could a speed be negative or imaginary? It's a scalar value measuring the magnitude of the velocity vector. Even when you're doing simple physics problems and choose your reference frame for measuring such that it shows up in your equations as negative, what you're really doing is discussing one-dimensional velocity - still a vector value, and not the same thing at all.
And of course that also ignores the fact that E=mc^2 is part of a much more complicated formula providing
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If negative mass and positive mass collide, what would happen? ...
I'm not positive...
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They are supposed to be opposites, and let's presume they cancel each other out ...
Well, no, let's not - at least not without good reason.
Positive mass and negative mass have oppositely-signed masses. Why would that mean they'd be opposite in all other ways?
I'm no particle physicist, but negative mass seems to integrate very poorly into the system here.
Or it could just be that, not being a particle physicist, integrating negative mass into "the system" could be beyond you. It's certainly beyond me, so I'm not even going to try.
And presumably negative mass would have particles of some sort
That's an awful lot of presumptions.
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Firstly, Dark Matter is hardly a new buzzword, it's been around for decades. And secondly, no it probably wouldn't.
Composition of the universe according to currently accepted cosmology: (from memory, the %'s are probably off a bit)
Normal matter ~= 5%
- everything we can observe directly
Dark Matter ~=20%
- Can only interact via gravity. To explain observations it must not be able to collide or clump together. Not even with other dark matter. Basical
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Balancing would be easy I would think, just use the negative mass as your reaction mass. Example:
Float in space next to a chunk of negative inertial mass with the the same absolute mass. Push on chunk - you move away from it, and an equal-but-opposite force pushes the chunk away from you. However the chunk's negative mass means that force generates an acceleration in the opposite direction: towards you. So you and the chunk travel through space in the same direction and speed, and any time you wish to a