Astrophysics and Cosmology - Discuss the Universe here

[zeebo]

This is dated and I don't know if it's accurate, but a kinda cool musing on photons.

http://www.propermotion.com/jwreed/Essays/The%20Life%20of%20A%20Photon.htm

[Agent : Orange]

All about tachyons, better than I could say it and right from the horse's mouth!

https://www.uam.es/personal_pdi/ciencias/jcuevas/Teaching/Taquiones.pdf
Enjoy!

[Agent : Orange]

This is dated and I don't know if it's accurate, but a kinda cool musing on photons.

http://www.propermotion.com/jwreed/Essays/The%20Life%20of%20A%20Photon.htm

This was a neat article. But the real punchline for me is that the observer's eye and Andromeda are the same place and time for the photon in that story!

[GeorgieForPresident2216]

All about tachyons, better than I could say it and right from the horse's mouth!

https://www.uam.es/personal_pdi/ciencias/jcuevas/Teaching/Taquiones.pdf
Enjoy!

Thanks for taking an interest in my questions and your answers.  That looks like a good comprehensive article, from a time when you could find in depth treatments like that  .  It should be very helpful.

[zeebo]

All about tachyons...

Tachyons are real?  I thought they were just a Star Trek Next Gen. device.  Will have to look into this.

[FearBoysWithBugs]

Tachyons are real?  I thought they were just a Star Trek Next Gen. device.  Will have to look into this.

You wouldn't be able to see a tachyon approach, but after it passed, you would see two images: one of it approaching, and another of it departing.

[Agent : Orange]

Tachyons are real?  I thought they were just a Star Trek Next Gen. device.  Will have to look into this.

They're not physically "real", but they do come from real theory. You can take physics and put exotic bits of math into it (like tachyons, or exotic matter, or whatever) and see what it would be like afterward. But it doesn't mean things are really like that.

[aldousburbank]

They're not physically "real", but they do come from real theory. You can take physics and put exotic bits of math into it (like tachyons, or exotic matter, or whatever) and see what it would be like afterward. But it doesn't mean things are really like that.

So, like a cosmic strip club?

[wr250]

They're not physically "real", but they do come from real theory. You can take physics and put exotic bits of math into it (like tachyons, or exotic matter, or whatever) and see what it would be like afterward. But it doesn't mean things are really like that.

its like you have 2 apples. you double the number of apple you have (2*2) for a total of four. but mathematically -2*-2=4 is also true and a mathematically valid answer.

[Agent : Orange]

So, like a cosmic strip club?

^^^ this.

You may only think what you're seeing is real.

[aldousburbank]

^^^ this.

You may only think what you're seeing is real.

I want to believe!

[Agent : Orange]

its like you have 2 apples. you double the number of apple you have (2*2) for a total of four. but mathematically -2*-2=4 is also true and a mathematically valid answer.

The problem is it may not make "sense" as we understand it to say a negative number (or imaginary) is at all valid for some quantities. Like magnetic monopoles. Maxwell's equations are set up to ignore magnetic "charges" since we have never seen one and thus we conclude they don't exist. If they did they could be accommodated easily. But such things have never been seen (and no evidence exists for them) so we discount them. Including them becomes and interesting mathematical game of "what if". It's tough to answer if such things might really be possible, which is why we need experiment to put physics on the right track.

[wr250]

The problem is it may not make "sense" as we understand it to say a negative number (or imaginary) is at all valid for some quantities. Like magnetic monopoles. Maxwell's equations are set up to ignore magnetic "charges" since we have never seen one and thus we conclude they don't exist. If they did they could be accommodated easily. But such things have never been seen (and no evidence exists for them) so we discount them. Including them becomes and interesting mathematical game of "what if". It's tough to answer if such things might really be possible, which is why we need experiment to put physics on the right track.

i should of qualified that as " -2*-2=4 might be valid mathematically, but makes no sense in the real world, and is thus discarded"

[aldousburbank]

i should of qualified that as " -2*-2=4 might be valid mathematically, but makes no sense in the real world, and is thus discarded"

Yeah well, don't let it happen again.

[GeorgieForPresident2216]

http://www.cbc.ca/news/technology/planetary-society-to-launch-solar-sail-test-flight-in-may-1.2932302

Long the stuff of science fiction, people are now experimenting with solar sails.  It's pretty cool to see citizen groups working on this kind of thing rather than having to rely on government.

http://www.youtube.com/watch?x-yt-ts=1421914688&x-yt-cl=84503534&v=bI_FH_2Cqr8#t=14

[Delphi]

I remember a pc game called Tachyon.. am I right?

[zeebo]

...Long the stuff of science fiction, people are now experimenting with solar sails.  ...

Those space jibs are cool but isn't the problem that once you get out past your own solar system the photons powering you drop off?  Or can you already get up to pretty good speed by then?

[GeorgieForPresident2216]

Those space jibs are cool but isn't the problem that once you get out past your own solar system the photons powering you drop off?  Or can you already get up to pretty good speed by then?

I suppose you would have to drift on your momentum... don't have a clue how much speed you could develop by then.  I've heard some musings about using lasers or directed energy shot out from the inner solar system to keep a solar sail ship powered in interstellar space.

[Kelt]

I suppose you would have to drift on your momentum... don't have a clue how much speed you could develop by then.  I've heard some musings about using lasers or directed energy shot out from the inner solar system to keep a solar sail ship powered in interstellar space.

I believe that was the plot in The Mote in God's Eye.

[wr250]

http://www.cnet.com/news/a-planetary-ring-system-200-times-the-size-of-saturns/

link says it all

[FearBoysWithBugs]

http://www.cnet.com/news/a-planetary-ring-system-200-times-the-size-of-saturns/

link says it all

Great article!  What an interesting discovery.

[ks3484]

<a href=http://www.space.com/28376-asteroid-2004-bl86-moon-nasa-video.html?cmpid=558948>Space.com: Big Earth-Buzzing Asteroid Has Its Own Moon</a>

The mountain-size asteroid that gave Earth a close shave Monday (Jan. 26) has its own moon, new radar images of the object reveal.

[Gd5150]

Theres an app called Luminos that tracks 1000's of comets, astroids, all the satellites. Will show you where they are in the sky and solar system at anytime within 10,000 years of today. I found BL86 on it, and flew by the Earth, its amazing. Check it out, its very cool!

[ks3484]

Theres an app called Luminos that tracks 1000's of comets, astroids, all the satellites. Will show you where they are in the sky and solar system at anytime within 10,000 years of today. I found BL86 on it, and flew by the Earth, its amazing. Check it out, its very cool!

I think that the graphics for Luminos are awe inspiring (or at least their web site is). But I've used - <a href=http://www.fourmilab.ch/homeplanet/>Home Planet</a> for years now - <a href=http://www.fourmilab.ch/homeplanet/download/3.3a/hp3full.zip>Download Home Planet "Full" Edition (14Mb)</a>; mainly because it's 100% free.

It's able to track asteroids, comets, meteors, spacecraft, space junk, the zodiac and anything else floating around in space.

The main reason that it's able to do those things and more is because the program is able to use the standard elements from any space program. A couple of the sites that I get my elements from is Space.com, Near Earth Asteroid Tracking - N.E.A.T., Near Earth Objects - N.E.O., Minor Planet Circulars - MPECs, and NASA.

[Agent : Orange]

Looks like the BICEP2 results on primordial B-modes (gravitational waves) in the early universe were incorrect after all. The joint paper they collaborated with the Planck team acknowledges they likely just detected polarization from galactic dust.
http://phys.org/news/2015-01-planck-gravitational-elusive.html
Too bad... but there may still be primordial B-modes lurking out there somewhere, waiting to be discovered.

Exciting times

[Agent : Orange]

Amazing paper just posted to the arXiv a few hours ago, the Keck array seems to argue for primordial B mode gravitational wave signature consistent with BICEP2 and not due to systematics.

http://arxiv.org/abs/1502.00643

The situation is even more exciting now! I'm sure this will attract a lot of discussion in the next few weeks...

No mention of dust or how to distinguish primordial B-modes from dust, but this says plenty about the ability to detect gravitational waves. Will be interesting to see what multiple frequency observations have to say about all of this.

[GeorgieForPresident2216]

Amazing paper just posted to the arXiv a few hours ago, the Keck array seems to argue for primordial B mode gravitational wave signature consistent with BICEP2 and not due to systematics.

http://arxiv.org/abs/1502.00643

The situation is even more exciting now! I'm sure this will attract a lot of discussion in the next few weeks...

No mention of dust or how to distinguish primordial B-modes from dust, but this says plenty about the ability to detect gravitational waves. Will be interesting to see what multiple frequency observations have to say about all of this.

This has more ups and downs than the unfolding Art Bell saga  .

[Agent : Orange]

This has more ups and downs than the unfolding Art Bell saga  .

Absolutely!

There's a lot on the line and the measurements are extremely difficult to make so people are scrambling for any clues they can find that will help in moving on.
There's still room for this to be a dust contaminated signal but we have to wait for the upcoming observations to know that for sure. What is clear is that there is a signal over what is expected from the standard cosmology and that signal remains consistent with BICEP2.

The previous BICEP2/planck paper from two days ago shows there is some contribution from dust in the B-mode signal, so that some of the signal must be the result of dust. But it does not mean all of it must be from dust. There's still room for primordial B-modes in the BICEP2 data. That's why its so important to get this new paper from Keck. Maybe there is something more interesting there beneath the surface that needed a better instrument to be studied. We'll see.

[GeorgieForPresident2216]

Keeping this thread alive, and seeing if this entire .gif will post.

The Sun so far this year.

[zeebo]

"Quasars separated by billions of light-years are lined up in a mysterious way. Astronomers looking at nearly 100 quasars have discovered that the central black holes of these ultra-bright, faraway galaxies have rotational axes that are aligned with each other. These alignments are the largest known in the universe.....These new findings indicate that the rotation axes of quasars tend to be parallel to the large-scale structures that they inhabit. That means that if the quasars are in a long filament, then the spins of their central black holes will point along the filament. According their estimates, there’s only a one percent probability that these alignments are simply the result of chance."

http://www.iflscience.com/space/quasars-across-billions-light-years-align-each-other