Astrophysics and Cosmology - Discuss the Universe here

[GeorgieForPresident2216]

No, that's not what I'm confused about.  The words "free fall" were used to describe Bob's motion.  As in, he started out at v = 0 and accelerated as he approached the black hole.  The curve of the blue line seems to make sense -- starts out slow, gets faster, and then slows down (from Alice's perspective) as he approaches the event

Oh okay, I got you.  I was a little confused about that too but quickly put it out of my mind.  Sorry to muddy the issue.

[DigitalPigSnuggler]

Oh okay, I got you.  I was a little confused about that too but quickly put it out of my mind.  Sorry to muddy the issue.  I've been listening to Noory too much I guess.

It's my fault.  I didn't even explain what was confusing me.  I don't know what has got into me today.

Continuing from the previous post....so the blue curve makes sense.  What doesn't make sense to me is how quickly the blue and red curves diverge.  I would expect there to be a period of time where they would track each other, or nearly so, but they go off and completely different angles.  Maybe it's the scale, I dunno.  But that is what I don't quite understand -- why the red and blue curves show no sign of agreement near t = 0.

[GeorgieForPresident2216]

You're good.  I was in a particular mindset.

[Agent : Orange]

I dropped Bob in only 5 distance units away from the hole, so there should already be some serious time dilation out there. It's only a few Schwarzschild radii away from the event horizon and innermost stable circular orbit. This means that small displacements cause big changes right out of the gate. Coupled with the somewhat squashed y-axis makes the disagreement look very large. If I had started Bob out further away then the curves would indeed track each other much more closely at the beginning. I should check more closely the scaling but I think it's right.

I agree that it was not the best choice to illustrate the effect, but I'd argue that it still makes the point I was trying to make.

[DigitalPigSnuggler]

I agree that it was not the best choice to illustrate the effect

I think it made your point very well.  It just looked odd to me and I wanted to be sure.  Thanks.  And a big sloppy kiss to Georgie for holding my hand until you could provide reassurance.

[Agent : Orange]

I'm pretty sure even in my 'scope I've only really seen the bright core of Andromeda they mentioned.  To pick up those wispy arms you need more optical horsepower I think. 

I do remember reading somewhere that it is the farthest object away you can see with the naked eye, which is pretty cool.  And I suspect most people don't realize how much crazier far away it really is. 

The bright star Vega is only 25 lt. yrs. away, while Andromeda is 2.5 million lt. yrs. from us ... 100,000 times farther away.   

Something to ponder whilst checking out Andromeda, is that the light you're picking up started it's journey to us around the very beginning of the Stone Age:

The Stone Age or Paleolithic Period is the name archaeologists have given to the beginning of archaeology--that part of the earth's history that includes the genus Homo and our immediate ancestor Australopithecus. It began approximately 2.5 million years ago, in Africa, when Australopithecus began making stone tools, and ended about 20,000 years ago, with big-brained and talented modern humans spread all over the world.

These posts made the hairs on the back of my neck stand up and gave me goosebumps. This is all converging on an extremely interesting and perhaps also somewhat obscure fact which makes me feel awe and reverence every time I really think about it.

As Zeebo very nicely said, the light rays that enter the pupil of our eye and form an image of the Andromeda galaxy on our retina began their journey to us when our species was still hanging from tree limbs. This is due to the finite speed of light, c, and the huge gulf of space between us and our nearest neighboring galaxy. From our perspective, the light ray takes a huge amount of time to make the trip from Andromeda to us. Now let's think a little more about objects moving close to the speed of light. We know from special relativity that no material object can move at the speed of light itself but you can approach it arbitrarily close if you have enough energy to get yoursef moving that fast. The faster you go, the slower and slower time seems to run relative to an observer at rest with respect to you. Thus, you can spend a year exploring the Universe at 0.99999999c, and return home to find centuries have passed in your absence but you have hardly aged at all. The catch is, no matter how fast you travel you will always age a little bit, because you just can't move at the speed of light. You have a finite, non-zero mass and the consequence of this means you can never get the energy you'd need to propel yourself along at the ultimate speed limit, c, the speed of light itself.

Now, light rays - photons - do not have such a restriction because they have no mass. They always move at c by their very definition. Since they are massless, photons travel on paths through space-time called null geodesics. These paths have very interesting and non-intuitive properties. Time is a little different to the massless particles that move along null geodesics than it is for material particles. While we see a photon taking a finite time to get to us, the photon itself does not experience time at all. To a light ray, no time passes from its emission and its absorption. This implies space doesn't really have much meaning for a photon either. In analogy to material particles this is an extreme example of Lorentz contraction and time dilation. Photons are the limit at which space and time are contracted and dilated away to entirely nothing. A light ray from Andromeda does not perceive any difference between the prehistoric age of the apes and us.

There is something deep and profound about this idea to me.

Since time is maximally dilated along a light ray, all the moments we experience between the photons creation to annihilation are "now" from it's point of view, and all points from the beginning to the end of it's trek is "here". This is an alien, holistic type of description of the Universe that is completely outside our every day experience and gives one of the best examples where mathematics has to lead over our intuition. It is a beautiful example of the truth in Einstein's words when he said "the distinction between past, present, and future is only a stubbornly persistent illusion".

It's pretty mindblowing to look at Andromeda and think about all of this. But even more so, consider what it means for a photon from the cosmic microwave background. For this photon, emitted at the time of last scattering only 300,000 years after the big bang, "today" and "then" are effectively identical, and the path it has taken through the 13 billion plus years getting to us is nothing more than a step. In that sense there is no distinction between the early Universe and today. In some way far outside our own limited perspective we are in direct audience of the origin of the Universe at every moment, no matter where we are, connected in an ephemeral way with the ultimate birth of whatever it is we mean when we say "reality". I'd be hard pressed to say that I have ever found a more awesome (or dare I use the term spiritual?) concept than that in my life.

[Agent : Orange]

And a few links from yesterday:

Signatures of starquakes found in giant flares from magnetars:
http://www.nasa.gov/content/goddard/nasas-fermi-satellite-finds-hints-of-starquakes-in-magnetar-storm/#.VEckUEvZAeE_______________________________________________
An equivalent of magnitude 23 quakes act on these neutron stars during their bursts, shattering their crusts and injecting the magnetic fields around them with huge atomic fireballs that are strong enough to affect Earth's magnetic fields even from light years away

POLARBEAR claims to see evidence of cosmological B-modes which measure gravitational lensing by substructure forming between now and the Universe's origin
http://ucsdnews.ucsd.edu/pressrelease/polarbear_detects_curls_in_the_universes_oldest_light
They may also have something to say about the BICEP2 results on primordial B-modes as well, since they also have two other papers in the chute. this makes the upcoming joint planck/BICEP2 paper even more interesting...

[GeorgieForPresident2216]

Originator of Inflationary cosmology Alan Guth to hold free live streaming event on World Science U tomorrow.

http://www.worldscienceu.com/courses/master_class/master-class-alan-guth

[GeorgieForPresident2216]

Thanks for your thoughts, Agent.

I think a lot about the nature of time and the significance of the speed of light in shaping of the Universe.  I find it fascinating that while we think of boundaries as being physical, the universe is bounded by a speed and all structure originates from that.  And of course it's not light itself that is important in that respect... it is just something that happens to travel at that upper boundary due to its lack of mass.  It almost seems, at least to me, that the singularity is what happens at that boundary of the speed of light, at least in the direction that it is traveling.  This all seems to point to light speed as a starting point for our Universe... not the end point that we tend to view it as.  Wouldn't that be a beautiful way to make a simulation?  Start everything out as a singularity and expand both time and physical space out from there based on a fixed information transfer rate.  And what if in this simulation you set that transfer rate to unity?  Then mass and energy would truly be 1:1 equivalent. 

I think we are only beginning to understand the nature of the universe, and I think the answers are locked up in the nature of time itself and its interaction with light speed and gravity -- or maybe it's all the same thing.  Maybe gravity is just the slowing down of information transfer because there is too much stuff to process.

[area51drone]

Agent,

If you have time, could you revisit these posts for me?  I've been waiting for you to comment on them, since, oh, July.  Not like you have to, but I would definitely like to hear your opinion.


http://bellgab.com/index.php/topic,4908.msg279650.html#msg279650
http://bellgab.com/index.php/topic,4908.msg279802.html#msg279802
http://bellgab.com/index.php/topic,4908.msg280074.html#msg280074
http://bellgab.com/index.php/topic,4908.msg297102.html#msg297102

[Agent : Orange]

Agent,

If you have time, could you revisit these posts for me?  I've been waiting for you to comment on them, since, oh, July.  Not like you have to, but I would definitely like to hear your opinion.


http://bellgab.com/index.php/topic,4908.msg279650.html#msg279650
http://bellgab.com/index.php/topic,4908.msg279802.html#msg279802
http://bellgab.com/index.php/topic,4908.msg280074.html#msg280074
http://bellgab.com/index.php/topic,4908.msg297102.html#msg297102

For sure I'll get back to this but it might be a few days.

[aldousburbank]

The faster you go, the slower and slower time seems to run relative to an observer at rest with respect to you. Thus, you can spend a year exploring the Universe at 0.99999999c, and return home to find centuries have passed in your absence but you have hardly aged at all. The catch is, no matter how fast you travel you will always age a little bit, because you just can't move at the speed of light. You have a finite, non-zero mass and the consequence of this means you can never get the energy you'd need to propel yourself along at the ultimate speed limit, c, the speed of light itself.

I hate when that happens.

[ComeBackArt]

Finally, a speed limit people actually have to follow.

[zeebo]

Speaking of the speed of light, I have a dumb question but here goes.   Is there something special about light as it relates to the fabric of spacetime?  Or, is it just that light is the only thing fast enough to be constrained by the global speed limit for anything in the universe (i.e. if the generic speed limit were higher, would light go faster)?

[GeorgieForPresident2216]

Speaking of the speed of light, I have a dumb question but here goes.   Is there something special about light as it relates to the fabric of spacetime?  Or, is it just that light is the only thing fast enough to be constrained by the global speed limit for anything in the universe (i.e. if the generic speed limit were higher, would light go faster)?

I'm not sure I can provide any special insight or tell you anything you don't already know, but hopefully this will be useful.  Special relativity says the speed of light is the limit at which all observers not traveling with a particle of mass x will see its momentum approach infinity -- an impossibility because there isn't enough energy in the universe to do this.  Particles without mass, however, do not require energy to overcome inertia so they automatically travel at light speed.  Photons are one such particle, but gluons and the hypothetical gravitons may also carry zero mass and therefore travel at this speed.  Neutrinos may as well but it is almost certain they do have some mass.

So I guess the simple answer to your question is that light simply adheres to the universal speed limit because photons carry no mass.  However, what is the underlying principle for this?  We say the speed of light is the maximum speed of information.  The carriers of information include photons, gluons, gravitons, and the weird W and Z bosons which actually do have mass.  Right now I'm trying to visualize the speed of light as a sort of processing speed for the universe something like the processing speed of your cpu, and photons as packets of information which mediate the transfer between memory locations, perhaps jumping form Planck volume to Planck volume.

With my limited knowledge I actually think your question is very profound and holds the key to understanding the nature of the universe.

[zeebo]

...Particles without mass, however, do not require energy to overcome inertia so they automatically travel at light speed.  Photons are one such particle, but gluons and the hypothetical gravitons may also carry zero mass and therefore travel at this speed....

Actually this helps me understand it better, thanks.  Light speed is one way to describe the max speed limit, but sounds like we could also say it's Massless Particle speed.  So the way I'm seeing it, is it's really the nature of mass that reveals the relativistic constraints, not necessarily light specifically.

[area51drone]

Why is it 186k miles per second though?  Why not 200k?  Why not 5,000,000?

[GeorgieForPresident2216]

Why is it 186k miles per second though?  Why not 200k?  Why not 5,000,000?

Idunno. 

186k miles/sec must equal unity in the units of the Great Programmer.

[aldousburbank]

Why is it 186k miles per second though?  Why not 200k?  Why not 5,000,000?

Dude, it's because our measure of "mile" is off by 186,000 x (60 X 60) percent. Think about it. 

[area51drone]

Saw this pic over on 4chan.   Hexagon?  Crazy

[GeorgieForPresident2216]

The Alma radio telescope took this image of a protostar, showing evidence of planets developing within the black rings.

[attachimg=1]

The star only started forming about one million years ago, or around the time our Homo Erectus ancestors were learning to harness fire.  Perhaps in another 4.6 billion years it will have its own hominids who think the Universe was created just for them.

http://www.bbc.com/news/science-environment-29932609

[Gd5150]

Homo Erectus

[zeebo]

Ok you guys are posting some cool pics - here's one from a few years ago you may have missed.  Hubble's shot of the huge globular star cluster Omega Centauri.  Note the newer, hotter blue stars and older, cooler red stars.



From wikipedia:  "Located at a distance of 15,800 light-years, it is the largest globular cluster in the Milky Way galaxy at a diameter of roughly 150 light-years. It is estimated to contain approximately 10 million stars and a total mass equivalent to 4 million suns".

[zeebo]

Interesting info on a new super-accurate atomic clock.  It's so sensitive apparently that it can pick up time differences between the floor and the ceiling.

The relative nature of time isn't just something seen in the extreme. If you take a clock off the floor, and hang it on the wall, Ye says, "the time will speed up by about one part in 1016."

That is a sliver of a second. But this isn't some effect of gravity on the clock's machinery. Time itself is flowing more quickly on the wall than on the floor. These differences didn't really matter until now. But this new clock is so sensitive, little changes in height throw it way off. Lift it just a couple of centimeters, Ye says, "and you will start to see that difference."

This new clock can sense the pace of time speeding up as it moves inch by inch away from the earth's core.

[area51drone]

That's pretty cool

[area51drone]

Coolest video you will see today:

http://www.cnn.com/video/data/2.0/video/tech/2014/11/06/astronauts-put-camera-in-water-bubble.nasa.html

[area51drone]

Check this out guys - very good pictures of 67P/Churyumov-Gerasimenko.   Tomorrow Philae lands!

http://kuow.org/post/researchers-attempt-robotic-landing-comets-surface

[area51drone]

The above referenced images... for those of you too lazy to click.   These were taken from 18 miles away.

[zeebo]

Check this out guys - very good pictures of 67P/Churyumov-Gerasimenko.   Tomorrow Philae lands! ....

Amazing technological feat to get this close to something so small that's hurtling through space so fast.  This is the kind of inspirational achievement that should lead the nightly news, not the usual parade of knuckleheads doing idiotic things.

[Robert Ghostwolf's Ghost]

Somebody should call RCH, because there appear to be some sort of mysterious artificial structures in that little valley.

[attachimg=1]