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Author Topic: dark matter?  (Read 5185 times)

MetalSlimeHunt

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Re: dark matter?
« Reply #15 on: January 21, 2014, 08:08:31 pm »

You're saying these things, and what I'm hearing is "FTL potential".
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LeoLeonardoIII

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Re: dark matter?
« Reply #16 on: January 21, 2014, 08:19:53 pm »

First they'll use it for advertising. Always do.
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Putnam

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Re: dark matter?
« Reply #17 on: January 21, 2014, 08:29:07 pm »

Antimatter has mass exactly the same way as normal matter does. Nothing we know of has "antimass" (which I'm guessing you mean negative mass by). At all. It's purely conjectural, almost thought-experiment level stuff.

wierd

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Re: dark matter?
« Reply #18 on: January 21, 2014, 08:36:41 pm »

That's exactly what I said.

"To date, no particles with antimass properties have been detected."

However, the concept is required for hawking radiation to work. Hawking radiation is theoretical, but the math looks sound.

I prefaced this with "If you sent a probe to a black hole and found hawking radiation, it implies antimass is real" followed by "antimass would have profound implications."

I fully understand what antimatter is. Antimatter and antimass are completely unrelated.
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MetalSlimeHunt

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Re: dark matter?
« Reply #19 on: January 21, 2014, 08:41:09 pm »

I wouldn't exactly call Hawking radiation theoretical. We can easily infer its existence through the knowledge that micro-black holes form all the time, and yet the universe has not collapsed into a singularity.
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wierd

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Re: dark matter?
« Reply #20 on: January 21, 2014, 08:45:22 pm »

Actually, micro black holes are also theoretical.

That is why the LHC was created to attempt to create some.
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Putnam

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Re: dark matter?
« Reply #21 on: January 21, 2014, 09:09:21 pm »

It's negative energy that's required for hawking radiation...

wierd

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Re: dark matter?
« Reply #22 on: January 21, 2014, 09:12:58 pm »

Hypothetical antimass is equivalent to negative energy, due to the relationship with general relativity.  Negative energy is just as hypothetical as antimass.

Specifically, if E=MC^2, then to have a negative E, you must have a negative mass term, or you must assert that there is such a thing as negative C. One of the terms must be negative for E to be negative.
« Last Edit: January 21, 2014, 09:16:08 pm by wierd »
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alway

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Re: dark matter?
« Reply #23 on: January 22, 2014, 12:02:02 am »

Right then, so here's how things actually work.

Dark matter: Dark matter is likely simply another type of massive (it has mass; not necessarily that it has a lot of it), undiscovered particle; undiscovered simply because it interacts extremely weakly. An example of a similar particle is the neutrino; the experimental verification of which required tanks containing hundreds of tons of a liquid, and then sifting through all that liquid to look for about 10 atoms a week which spontaneously changed into another element as predicted (turns out they actually only found 3 a week, leading to the discovery of different types of neutrinos). So yeah, dark matter is pretty mundane in all likelyhood.

Antimatter: Antimatter is similar to matter; identical is basically every aspect. Not only has it been discovered, but we use it on a routine basis in things like PET scans (Positron Emission Tomography), which make use of antimatter emitted by a radioactive tracer to create their images. Antimatter is essentially identical to their matter pairs; and only differ in a very few known reactions. They have the opposite charge of their matter counterparts. When antimatter and matter meet, they annihilate, releasing energy in the form of photons or other force carrying particles. Their mass, however, is positive.

Dark Energy: Dark Energy is a big mystery. It is of entirely unknown origin, and is a strong, negative energy. It is responsible for the acceleration of the universe's expansion, in contrast to the expectation of a deceleration that was predicted by Einstein's theories of gravity. When this one is discovered, it will likely revolutionize physics, and generally turn everything we know on its head. We're talking potential for perpetual motion machine level of revolution here. So that's the one discovery to look forward to.

Virtual particles: Virtual particles exist as pairs, consisting of both matter and antimatter. They effectively live on 'borrowed energy' and spontaneously arise from nothing. Turns out, nature really abhors a vacuum. As a result, on the small scale, there is what is referred to as the 'quantum foam,' which consists of a soup of such virtual particle pairs, zipping in and out of existence. Part of quantum theory dictates that space, time, and energy are all quantized, and as such have a minimum size; a particle must have above certain thresholds of these values. Virtual pairs, to my understanding, live in the margins of these values; having small enough existences as to avoid some of the normal rules. To my understanding, these play a massive part in quantum field theory, and are effectively the things responsible for carrying things like magnetic forces. They zip into existence at the same point, fly apart, then back into one another and annihilate almost immediately.

Hawking radiation: Hawking radiation ties in very closely with virtual pairs, as they are the cause of the negative energy. In Hawking radiation, the virtual pair zips into existence right on the edge of the black hole's event horizon. The two fly apart momentarily, when suddenly one falls into the event horizon, and is unable to return. The other becomes a particle, and flies away. This basically creates an energy deficit, since the virtual pairs existed on borrowed energy; this is then basically taken from the black hole itself. Thus, to an observer, the black hole spawns a particle, the black hole losing energy equal to the particle's mass, right next to the event horizon, which then escapes as Hawking radiation. You can actually do something similar with lasers; which likewise turn virtual pairs into particles at the expense of energy. http://www.newscientist.com/article/mg20727744.200-lasers-could-make-virtual-particles-real.html
Which also means there is an upper limit to the power you can make a laser.  ;)

tldr; version, use wikipedia, it works.
« Last Edit: January 22, 2014, 12:07:16 am by alway »
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miauw62

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Re: dark matter?
« Reply #24 on: January 22, 2014, 07:45:22 am »

Hypothetical antimass is equivalent to negative energy, due to the relationship with general relativity.  Negative energy is just as hypothetical as antimass.

Specifically, if E=MC^2, then to have a negative E, you must have a negative mass term, or you must assert that there is such a thing as negative C. One of the terms must be negative for E to be negative.
Isn't C^2 always positive anyway?
« Last Edit: January 22, 2014, 07:48:13 am by miauw62 »
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Re: dark matter?
« Reply #25 on: January 22, 2014, 02:19:58 pm »

My favorite pet theory is stellar wormholes, smearing mass between connected stars and doing funky things to the inverse square law. If wormholes -did- exist, it seems likely they'd take up residence inside something energetic enough to mess with them/create them(?) I thought of it a long time ago, got shot down for no particular reason, and later found out some random researchers in Kyrgyzstan published a legitimate paper suggesting it. It's probably been examined and disproven, but I have no idea where to look for that part :D
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andrea

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Re: dark matter?
« Reply #26 on: January 22, 2014, 02:26:02 pm »

Isn't C^2 always positive anyway?

you would need to have imaginary C to have a negative C^2

MonkeyHead

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Re: dark matter?
« Reply #27 on: January 22, 2014, 02:29:28 pm »

Damn, late to the party, and on my specialist subject as well. Ahwell, nothing more to add, just PTWing incase my powers are needed.

Il Palazzo

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Re: dark matter?
« Reply #28 on: January 22, 2014, 03:04:54 pm »

Matter is to energy as dark matter is to dark energy
This is not true. They have nothing to do with each other, apart from the bad naming convention.

Negative energy is just as hypothetical as antimass.

Specifically, if E=MC^2, then to have a negative E, you must have a negative mass term, or you must assert that there is such a thing as negative C. One of the terms must be negative for E to be negative.
What, you mean like gravitational potential energy? Or any binding energy for that matter?

I'd advise against haphazard use of E=mc^2. For one, it's not the complete form of the equation. Also, it doesn't always apply.

See post #4 here: www.physicsforums.com/showthread.php?t=725315 for more details.
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Putnam

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Re: dark matter?
« Reply #29 on: January 22, 2014, 04:49:50 pm »

Although, there is a theory that matter is actually just energy that has been condensed.

And the prevailing one, at that.

Anyways, dark matter is matter that we cannot really see via the e.m. spectrum, hence the 'dark' (same applies to the energy). Dark Matter has mass, and so attracts other particles with mass. Dark Energy repulses things with mass.

Not quite. Dark matter is pretty much that, but dark energy is just the thing what makes the universe's expansion accelerate. Nothing more than that. We don't know if it's a repulsion affect or whatever.
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