Astrophysics and Cosmology - Discuss the Universe here

[zeebo]

Comet Lovejoy.  I saw it with my binocs, but it just looked like a very faint greenish nebula.  Here's a better pic.

[zeebo]

Radio wave blasts from unknown source.  E.T. phoning home?  The Millenium Falcon making the jump to light speed?

http://disinfo.com/2015/01/cosmic-burst-radio-waves-unknown-source-universe/

[zeebo]

What landscape photos would look like if planets replaced the Moon

[GeorgieForPresident2216]

What landscape photos would look like if planets replaced the Moon

The Earth would only be a small moon for Jupiter or Saturn  .

[wr250]

Radio wave blasts from unknown source.  E.T. phoning home?  The Millenium Falcon making the jump to light speed?

http://disinfo.com/2015/01/cosmic-burst-radio-waves-unknown-source-universe/

thats the cosmic reaction to the noorons radio waves spreading out into the universe...

[ks3484]

I suspect that worm holes are generated by suns or stars. In other words they are gateways to other dimensions, galaxies, and universes. I believe that if one were to travel through a worm hole they would exit at, or within the star that is generating the worm hole. Suns are gateways, or stargates if you will. I believe that suns, or stars are the only things in space and time with enough energy to power stargates.  ......just a thought..

[FearBoysWithBugs]

What landscape photos would look like if planets replaced the Moon

That was a fun little article, thanks for posting it.

[FearBoysWithBugs]

The New Horizons camera will begin shooting pictures of Pluto beginning this Sunday.

[Zoo]

Fact light travels slower in a vacuum. I care not what other people or books say or think. Facts are facts!!1

[FearBoysWithBugs]

Fact light travels slower in a vacuum.

Slower than what?

[Yorkshire pud]

Fact light travels slower in a vacuum. I care not what other people or books say or think. Facts are facts!!1

Is this a variation from light only travels in an atmosphere?

[zeebo]

That was a fun little article, thanks for posting it.

Glad you enjoyed - I always love pics that could be a sci-fi book cover.   

[zeebo]

The New Horizons camera will begin shooting pictures of Pluto beginning this Sunday.

Very cool.  Amazing really that they can pinpoint something so far away. 

[Agent : Orange]

Fact light travels slower in a vacuum. I care not what other people or books say or think. Facts are facts!!1

Can you define vacuum for us?

[FearBoysWithBugs]

Can you define vacuum for us?

The space between his ears?

[Agent : Orange]

neutrinos faster than light?


http://phys.org/news/2014-12-faster-than-light-particles.html


i find the article poorly written, perhaps agent : Orange can chime in when he finds time.
i was put off at the beginning where it is stated that : mathematically an imaginary number is the square root  of a negative number ,written bi where

Code Select Expand

i=−b^2, not the square. perhaps it works differently with mass equations (but i doubt it), or they mean

Code Select Expand

−b^2 . a negative number squared is always a positive number. EX: -22 (-2 multiplied by -2) is 4 (not -4) .


note i had to use the code tags to prevent autoformatting ,which made a huge mess of the post.

a month later i figure that the equation above is wrong. probably due to autoformatting.

-b^2 is -b squared which would be a postive number.
what was meant was i=SQROOT of -b

An imaginary number is written with i^2 = -1. So (i x m)^2 = -m^2
Or, if you like things in terms of square roots, sqrt( -m^2 ) = i x m, or just im if you prefer.

There are three kinds of paths particles can take through space-time in general relativity. These are defined in terms of path lengths or proper times, the time an observer travelling on that path would record on a watch they carried with them.

Time-like paths are the trajectories normal particles follow. These particles have positive mass like all of the matter we know. They move through time from the past to the future (though the rate at which they can be said to move from the past to the future is relative of course ) and they have speeds less than the speed of light. The proper time measured along this path is always positive, so causality is preserved for normal matter. As we would expect these particles all have positive mass that is real (which was good news for Einstein).

Null paths are the trajectories that light-rays follow. In fact, any particle with no mass (m=0) will follow one of these paths. The proper-time along these paths is 0, which means that light rays themselves don't experience time (which is infinitely fascinating to me). These kinds of paths are called null geodesics. Particles with no mass move at the speed of light always.

Space-like paths are the opposite to time-like paths, they are directed from the future to the past, and have proper times that are negative! Since energy must always be positive, the particles travelling along space-like paths are imaginary mass particles that must travel at speeds greater than the speed of light. In fact, the energy-velocity relationship is upside down for these kinds of particles. The slower they go, the more energy they have, which is weird and counter-intuitive. These kinds of particles are not widely considered realistic and when a tachyon shows up from a quantum field type of calculation then the theory is considered flawed and there's something wrong with the assumptions that have gone into developing it. These particles make all kinds of strange trouble for the universe and a lot of people have looked at what kind of paradoxes might exist if they were kicking around the universe.

So that article posted earlier is about trying to find such past-directed particles. But there are some big problems with this guys idea. The main one is that his claim hinges on the neutrino being a negative mass particle. Ehrlich claims the mass bound on neutrinos is -0.11 +- 0.016 electron Volts. (from his article here which i have not read http://arxiv.org/abs/1408.2804). That may be, but the observations and experiments with neutrinos are still in their infancy and are not anywhere near precise enough to make the claim the neutrino really has a tiny and negative mass. So I would be suspicious of the whole thing and take it with a salt-shaker full of salt instead of just a few grains.

Still it would turn established physics on it's head so if there's still a possibility let's go do some small experiments first like the ones mentioned in the original article (ie using tritium beta decays and cosmic ray data) before we treat it any more seriously.

Blowing a kneecap off of an established idea is the dream of every theorist.

However, in closing, let me say this

Don't worry about it, the imaginary number isn't really there.   

is wisdom

[Agent : Orange]

Very cool.  Amazing really that they can pinpoint something so far away.

New Horizons was launched in 2006 (or around that) and is expected to enter orbit around Pluto this July... so there will be a ton of closeups coming soon!

[Agent : Orange]

Let me also say that Maxwell's laws also allow for solutions to the electromagnetic wave equation that travel backward through time! We are used to the solutions which are time-delayed which represents the finite speed of light effect - it takes a while for signals to travel through space. Before relativity in classical electromagnetism this has to be put in by hand. You could just as easily put in "advanced" effects just as easily, where the influence travels the other way from future to past. Then when you solve the wave equations you find electromagnetic waves - light rays - that travel backward in time. These solutions are just thrown away as "unphysical" which they are since we've never observed such things. But experiments have been done to try to find them if they are real!

So it's interesting that these kinds of features survived from classical mechanics into GR where causality is strictly enforced for ordinary matter. Maybe there's something to it. Or it may be the next theory will utterly kill them off completely once we understand quantum gravity properly.

[Agent : Orange]

Comet Lovejoy.  I saw it with my binocs, but it just looked like a very faint greenish nebula.  Here's a better pic.

This is a very nice image. I stood around with some friends outside our building on campus to try to get a view in -35 degrees ( C or F, it doesn't really matter when it's that cold). One guy didn't have a coat so we weren't out for long... 
Otherwise haven't had a chance to get much of a view at all though the pictures I've seen (like this one) have looked beautiful.

[FearBoysWithBugs]

expected to enter orbit around Pluto

I think it is moving too fast to do that.  But agree that the images will be sexy.

[Agent : Orange]

I think it is moving too fast to do that.  But agree that the images will be sexy.

My mistake, it is scheduled for flyby summer this year. Then on off to more of the Kuiper belt. Interesting post about followup KBO targets here
http://www.planetary.org/blogs/emily-lakdawalla/2014/10151024-finally-new-horizons-has-a-kbo.html.

[FearBoysWithBugs]

My mistake, it is scheduled for flyby summer this year. Then on off to more of the Kuiper belt. Interesting post about followup KBO targets here
http://www.planetary.org/blogs/emily-lakdawalla/2014/10151024-finally-new-horizons-has-a-kbo.html.

Might be me, but that link did not work for me.  The site comes up but not the article.

[Agent : Orange]

Might be me, but that link did not work for me.  The site comes up but not the article.

Bizarre.
http://www.planetary.org/blogs/emily-lakdawalla/2014/10151024-finally-new-horizons-has-a-kbo.html
Did that work?

Regardless... interesting stuff is afoot.

[GeorgieForPresident2216]

Fact light travels slower in a vacuum. I care not what other people or books say or think. Facts are facts!!1

I tried to look down the nozzle of my vacuum when I got some hair stuck in there, and I couldn't see any light at all.

[GeorgieForPresident2216]

Agent, can I infer from your discussion that a hypothetical particle of negative mass would necessarily travel faster than light and with negative time progression?

Also, something which has long bothered me:  is it possible such particles could be confined to the great voids between galactic clusters and walls in the large scale structure of the universe?  Is it possible they could be creating a repulsive force compressing areas of ordinary matter together -- perhaps being interpreted as dark energy or contributing to the appearance of dark matter?


I suppose if they did travel faster than light it wouldn't make any sense for them to be confined in that way.

[FearBoysWithBugs]

Bizarre.
Did that work?

Yes, thanks.  Apparently the period at the end of the first link gummed it up.

[wr250]

to be clear matter with negative mass is not antimatter (which is matter with reversed charge, IE an anti-electron has a positive charge, anti-proton has a negative charge).

[GeorgieForPresident2216]

to be clear matter with negative mass is not antimatter (which is matter with reversed charge, IE an anti-electron has a positive charge, anti-proton has a negative charge).

Indeed.  Matter with negative mass would have negative inertia and possibly negative gravity? which would be strange indeed.  I'm not sure such a thing is possible but I have been curious since the late 90s whether it could be an explanation for the great voids and large scale structure, and some of the effects we see, like the Great Attractor, which I propose is really the Great Repulsor, as two great voids attempt to merge.  It's probably pretty silly, but that's what I'm here to find out. 

[Agent : Orange]

Agent, can I infer from your discussion that a hypothetical particle of negative mass would necessarily travel faster than light and with negative time progression?

Also, something which has long bothered me:  is it possible such particles could be confined to the great voids between galactic clusters and walls in the large scale structure of the universe?  Is it possible they could be creating a repulsive force compressing areas of ordinary matter together -- perhaps being interpreted as dark energy or contributing to the appearance of dark matter?


I suppose if they did travel faster than light it wouldn't make any sense for them to be confined in that way.

Negative mass is a bit of a different exotic something. Negative mass would still give m^2, and imaginary mass like the kind discussed earlier on in the article posted would give back a -m^2. That - sign makes all the difference. Such stuff if it existed would have to have v>c always and the standard energy relationship would be flipped - as it moved faster and faster it would have less and less energy.

I would argue the lack of a ground state (E=0 would occur only at v=infinity) would be a case against this kind of matter. And I would need a good argument to believe neutrinos might be this stuff.

Anyway even imaginary mass should still have positive energy and would still (presumably) affect gravity in the same way as normal matter in general relativity.

[Agent : Orange]

Indeed.  Matter with negative mass would have negative inertia and possibly negative gravity? which would be strange indeed.  I'm not sure such a thing is possible but I have been curious since the late 90s whether it could be an explanation for the great voids and large scale structure, and some of the effects we see, like the Great Attractor, which I propose is really the Great Repulsor, as two great voids attempt to merge.  It's probably pretty silly, but that's what I'm here to find out.

Theorists love to talk about "exotic matter" which is pretty much just negative energy (or negative mass) to stabilize finnicky solutions. It's how we got started talking about traversible wormholes and warp drives. It can give interesting mathematical behavior in some cases and even if it's not physical it might make a solution interesting in a different way.

It's basically the equivalent of "yes, and" for a theorist.

Certainly some kinds of physical effects are measurable and related to negative energy (like the Casimir effect http://en.wikipedia.org/wiki/Casimir_effect), but it's not really understood yet how it can be used or in what quantity or what real applications such things may yet have.