Astrophysics and Cosmology - Discuss the Universe here

[zeebo]

Immortal dreams in a mortal being... what kind of dick would plan that?

I heard a comedian say once, that God has a sense of humor.  He used the example of a guy hanging from a cliff, and then, in his most desperate moment, his palms start sweating.  Now that, that is some funny shit.

[area51drone]

I heard a comedian say once, that God has a sense of humor.  He used the example of a guy hanging from a cliff, and then, in his most desperate moment, his palms start sweating.  Now that, that is some funny shit.

   Dead children too.  God loves dead kids, shit, he demanded they be killed in the Bible.  It's all "part of His plan."

But really, I hate these conversations, they go no where to someone who is a true believer.  If we want to start a new thread to discuss this crap, I'd be more than happy to quickly explain why at least Christianity is bullshit.

[zeebo]

...I hate these conversations, they go no where to someone who is a true believer.  If we want to start a new thread to discuss this crap, I'd be more than happy to quickly explain why at least Christianity is bullshit.

I agree, if a religious maelstrom is about to break out, let's fork it into a new thread and keep this one for topics which are imho far more interesting like black holes and dark matter and the nature of spacetime etc.   

Here's one.  Is there any experiment going on either in some physics lab on earth or through some astronomical study of the cosmos which will shed any light on if string theory is legit or not?  In fact can string theory actually ever be proven at all even with some advanced technology, considering how tiny the strings are supposed to be, or will it be doomed to remain in the realm of mathematical theory?  (Einstein's theories of relativity were pretty far out at the time but at least as I understand it they made some predictions that could theoretically be tested sometime in the future.)

[Agent : Orange]

I agree, if a religious maelstrom is about to break out, let's fork it into a new thread and keep this one for topics which are imho far more interesting like black holes and dark matter and the nature of spacetime etc.   

Here's one.  Is there any experiment going on either in some physics lab on earth or through some astronomical study of the cosmos which will shed any light on if string theory is legit or not?  In fact can string theory actually ever be proven at all even with some advanced technology, considering how tiny the strings are supposed to be, or will it be doomed to remain in the realm of mathematical theory?  (Einstein's theories of relativity were pretty far out at the time but at least as I understand it they made some predictions that could theoretically be tested sometime in the future.)

Yeah there are many ongoing experiments and very interesting at that. String theory depends on something called supersymmetry and this means there should be many more particles than we currently know of. The scale of these particles is not addressed by the theory so no one knows the masses of such super particles ("sparticles" in the parlance) so we don't know what energy scales they should show up at. So far none have been found in the LHC which rules out the existence of the lowest energy sparticles. Other experiments like the ACME experiment have made precise measurements of the properties of the electron that rule out larger portions of the energy landscape where the sparticles can hide (see this article for some more details http://arstechnica.com/science/2013/12/thorium-put-to-use-kills-a-few-more-versions-of-supersymmetry/).

Despite the energy scales needed by string theory there are high energy cosmic rays which enter our atmosphere all the time. These naturally accelerated particles might give the best chance to observe some aspect of string theory. I suspect we'll need something like that to make definitive tests of the ideas because string theory effects are far outside our technological reach when it comes to accelerators.

[area51drone]

So Agent, if two smaller energy wave crests pass each other, is that when a particle pops in and out of existence as we hear in all these physics shows - they say "particles pop in and out of existence all the time"..?

[Agent : Orange]

So Agent, if two smaller energy wave crests pass each other, is that when a particle pops in and out of existence as we hear in all these physics shows - they say "particles pop in and out of existence all the time"..?

It might seem like a subtle distinction but "energy wave crests" are the wrong way to think about these things. All wave phenomena transport and carry energy but they require a physical medium to oscillate in order to propagate any kind of wave. The physical media that carry these waves are the fields that are associated with each kind of particle, or the "force fields" that describe bosons like the electromagnetic field for photons. The waves themselves are associated with material particles are actually what we understand to be waves of probability (http://en.wikipedia.org/wiki/Wave_function). This says that where probability waves are the highest (ie, at the position of maximum amplitude of the wave) we are the most likely to find a particle. Where the waves are minimal, we are unlikely to find any particle. Each probability wave carries some amount of energy, at minimum the rest energy of the particle it's describing. 

This is all regarding the uncertainty relation, position and momentum are related by a Fourier transform, such that the more localized a particle the larger the spread in momentum and vice-versa. Probability waves like any other kind of wave interfere with one another, and can add together (constructive interference) and negate one another (destructive interference). This is the explanation behind the double slit experiment. Wave-particle duality (http://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality) is among the most surprising and counter intuitive ideas of quantum mechanics.

[maureen]

It's such a delight to read such cogent postings. Thank you all for engaging my mind!

[area51drone]

It might seem like a subtle distinction but "energy wave crests" are the wrong way to think about these things. All wave phenomena transport and carry energy but they require a physical medium to oscillate in order to propagate any kind of wave. The physical media that carry these waves are the fields that are associated with each kind of particle, or the "force fields" that describe bosons like the electromagnetic field for photons. The waves themselves are associated with material particles are actually what we understand to be waves of probability (http://en.wikipedia.org/wiki/Wave_function). This says that where probability waves are the highest (ie, at the position of maximum amplitude of the wave) we are the most likely to find a particle. Where the waves are minimal, we are unlikely to find any particle. Each probability wave carries some amount of energy, at minimum the rest energy of the particle it's describing. 

This is all regarding the uncertainty relation, position and momentum are related by a Fourier transform, such that the more localized a particle the larger the spread in momentum and vice-versa. Probability waves like any other kind of wave interfere with one another, and can add together (constructive interference) and negate one another (destructive interference). This is the explanation behind the double slit experiment. Wave-particle duality (http://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality) is among the most surprising and counter intuitive ideas of quantum mechanics.

I thought the wave particle duality experiment was a perfect example of what I said.  In fact, I don't much see the difference, except that the wave may be more bumpy than just a standard sinusoidal wave.   I guess I have some reading to do to understand what the difference between a probability wave and a regular wave is.   (this looks like good reading: http://en.wikipedia.org/wiki/Wave_packet)   I understand what you're saying that the probability wave must be in a field.   Where does the field come from, or is it just there, surrounding everything?  Is my understanding correct that the higgs field is just everywhere and probability waves of a certain amplitude traveling through the higgs field is what makes particles/mass?

[Agent : Orange]

I thought the wave particle duality experiment was a perfect example of what I said.  In fact, I don't much see the difference, except that the wave may be more bumpy than just a standard sinusoidal wave.   

The wave is exactly sinusoidal in the double slit experiment but looks bumpy because there's only zero probability of finding a particle at well defined fringes. So if you were able to throw an infinite number of particles through so that the entire screen was covered you should find the density of particle detections go as a sin wave would predict. Actually to be exactly precise the probability itself is the square of the wave (the amplitude) since sin waves are half negative and there is no such thing as a negative probability.

I guess I have some reading to do to understand what the difference between a probability wave and a regular wave is.   (this looks like good reading: http://en.wikipedia.org/wiki/Wave_packet)   

It's a subtle point but it's an important distinction and it's the answer to your question of what happens when two wavefronts cross one another. Depending on how they interfere with one another you get either constructive or destructive interference. Where constructive interference occurs there's an enhanced probability of finding the particle and less chance to find it in destructively interfering parts of the waves passing. It doesn't mean that energy waves cause a particle to pop into existence anywhere on the screen, just that there is a particle "somewhere" because this wave passes by and the amplitude of the wave tells us what chance we have of finding it at a given point. Again it's a subtle distinction but by definition energy is a scalar property of an object, including waves, which have vector qualities. A wave has a direction of propagation and an amplitude, so a wave can carry energy but have to be described in terms of disturbances of some physical medium whether that is the air (sound waves), water waves or say, through a crystal lattice (phonons). Probability waves are no different except that they can be thought of as waves through distinct physical fields.

Wave packets are more complicated yet again because there's not one single frequency like a sine wave but a sum of frequencies that cancel out pretty much everywhere except at one location which is the description of a spatially localized particle as a set of waves. Again, back to Fourier transforms if you know the math behind those.

I understand what you're saying that the probability wave must be in a field.   Where does the field come from, or is it just there, surrounding everything?  Is my understanding correct that the higgs field is just everywhere and probability waves of a certain amplitude traveling through the higgs field is what makes particles/mass?

They come from the big bang, the fields are the quantum description of what it means to live in a universe in which there are particles like electrons and quarks. There must be electron and quark fields that can be disturbed in a wave-like kind of way. There's also a Higgs field, in which waves make up the Higgs particles and the interactions of those particles with any others causes what we observe as mass.

[Agent : Orange]

It's such a delight to read such cogent postings. Thank you all for engaging my mind!

Hi Maureen, welcome to the party.

[zeebo]

Yeah there are many ongoing experiments and very interesting at that. String theory depends on something called supersymmetry....

Great reply Agent, thanks.   I soo want to know if it's real or just a result of too many mathematical geniuses with over-caffeinated brains. 

Btw I just listened to a podcast where I was somewhat surprised to hear a theoretical physicist named Lee Smolin basically declare string theory a dead end, and instead promote something called Loop Quantum Gravity.  If interested it's here starting at 30:34.  (Also, on same podcast, and worth checking out, there's a segment about the search for gravity waves by using pulsars, starting at 19:17.)

http://bigpicturescience.org/episodes/Invisible_Worlds

(For those not already aware, lots of great free podcasts on this site - if you can look past the goofy skits & puns - it's run by Seth Shostak & co. at SETI, just click on Archives link at top for more.)

[Agent : Orange]

Great reply Agent, thanks.   I soo want to know if it's real or just a result of too many mathematical geniuses with over-caffeinated brains. 

Btw I just listened to a podcast where I was somewhat surprised to hear a theoretical physicist named Lee Smolin basically declare string theory a dead end, and instead promote something called Loop Quantum Gravity.  If interested it's here starting at 30:34.  (Also, on same podcast, and worth checking out, there's a segment about the search for gravity waves by using pulsars, starting at 19:17.)

http://bigpicturescience.org/episodes/Invisible_Worlds

(For those not already aware, lots of great free podcasts on this site - if you can look past the goofy skits & puns - it's run by Seth Shostak & co. at SETI, just click on Archives link at top for more.)

I know of Lee Smolin, he is one of the huge outspoken proponents of LQG and is vehemently anti-string theory. There are many others that are more visible who are supporters of string theory (Kaku, Greene, etc). So depending on who you ask you will get different reports on the health of string theory. In pretty much any case where there are two camps arguing for "this" or "that", I wouldn't be surprised if both are wrong and the truth is somewhere in the middle. It's on weaker footing than dark matter in my opinion, which is maybe a surprising thing to say, but at least there we have hints that we are moving in the right direction. String theory is very beautiful mathematically but loaded with speculation and conjecture. And we really have no way of knowing (yet) whether it's foundations are built on solid ground or swampland. String theory (at least the lowest energy cases that we have a hope of detecting) has been constrained strongly in the past few years, and it does not look like any of the forms accessible to us in the low-energy regime are still on the table. LQG has taken it's bumps as well, and I'm just not sure either is the correct path. To be honest, the best outcome may be that both turn out to be wrong and send all of the theoreticians back to the drawing board!

You bring up another interesting subject as well, gravity waves have not yet been directly detected. I guess during that show they mention the binary pulsar system that got Hulse and Taylor a Nobel prize (http://en.wikipedia.org/wiki/PSR_B1913%2B16)?

If not...

The Hulse and Taylor binary pulsar system is a pair of neutron stars that are orbiting around one another and losing energy in the exact amount that Einstein says they should be losing due to gravitational radiation. These gravitational waves that are carrying away orbital energy from the system are predicted by general relativity, they are waves that travel through space-time itself (!!), waves of space-time curvature, that propagate at the speed of light, similar to how light itself propagates through an electromagnetic field. Thus the two pulsars are moving closer and closer to one another as they lose energy to these gravitational waves. For a long time people have set up experiments to try to detect gravitational waves directly but these experiments have not yet been successful (http://en.wikipedia.org/wiki/Gravitational_wave). Much like dark matter, we expect these waves to be propagating around out there, because this system (and now a variety of others as well) so clearly show that gravitational radiation plays an active role in orbital dynamics but we have not yet observed them directly.

Gravitational waves will open a whole new window on the universe and allow us to see back farther than ever before, beyond the cosmic microwave background and in principle all the way back up to the big bang itself at t=0. In fact there should be old "relic" waves from the origin of the universe still propagating around out there, but slowly getting weaker. At the origin of the universe we expect the entire universe should have rung like a gong, and it should be possible to detect those oscillations.

Far out.

Also thanks for the podcast suggestion, I will try to listen later on in the day.

[maureen]

the dichotomies of life so well stated makes for a lovely party!!.. and for a giggle I have made gravitational radiation my new oxymoron 

[zeebo]

...Gravitational waves will open a whole new window on the universe and allow us to see back farther than ever before, beyond the cosmic microwave background and in principle all the way back up to the big bang itself at t=0. In fact there should be old "relic" waves from the origin of the universe still propagating around out there, but slowly getting weaker. At the origin of the universe we expect the entire universe should have rung like a gong, and it should be possible to detect those oscillations.

That is really cool.  What amazes me, if I understand it correctly, is that the gravity waves would actually ripple across the spacetime fabric itself, slightly distorting it as it flows along.  I think that's what that pulsar experiment is trying to detect, by looking for some kind of time-warp blip in the pulsar's otherwise very regular pulses when the wave passes through one. 

[Agent : Orange]

That is really cool.  What amazes me, if I understand it correctly, is that the gravity waves would actually ripple across the spacetime fabric itself, slightly distorting it as it flows along. 

Yes this is true. As gravitational wave moves through the Earth, the planet is stretched by a tiny amount in one direction and compressed in the other. The same thing happens to us as gravitational radiation passes through our bodies! An illustration on a ring of particles, from the wiki I linked to earlier:

This effect is actually the key to trying to detect these things directly.

I think that's what that pulsar experiment is trying to detect, by looking for some kind of time-warp blip in the pulsar's otherwise very regular pulses when the wave passes through one.

Hulse and Taylor detected the orbital frequency, that is to say the rate at which the pulsars orbit one another, decreasing in exactly the way predicted by general relativity. That's why they won the Nobel prize for their work. It was significant in that it was the first real test of the gravitational wave prediction of general relativity and once again (as in all known cases) Einstein passed again with flying colors.

However, no one has still *directly* observed a gravitational wave. Their presence and effect are inferred by using systems of orbiting bodies similar to the system Hulse and Taylor studied. So the goal now is to observe gravitational waves directly using a gravitational wave detector (http://en.wikipedia.org/wiki/LIGO).

[West of the Rockies]

God, I love this stuff!

[zeebo]

...So the goal now is to observe gravitational waves directly using a gravitational wave detector (http://en.wikipedia.org/wiki/LIGO).

Ah so that's the LIGO the scientist (Scott Ransom) referenced in that podcast.  He said they were considered more likely to be successful than his experiment but you never know.  His way is discussed here: http://nanograv.org/.  Here's the gist:

Pulsars are rapidly rotating stars. A pulsar emits beams of radio waves which, like lighthouse beams, sweep through the sky as the pulsar rotates. The signal from a pulsar can be detected by radio telescopes as a series of regularly spaced pulses, essentially like the ticks of a clock. In fact, for the purposes of this experiment, it's useful to think of the pulsars as clocks. Gravitational waves affect the time it takes the pulses to travel from the pulsar to a telescope on Earth. We seek out perturbations due to gravitational waves in measurements of pulse arrival times at a telescope, in other words, we look for deviations in the clock ticks!

[Agent : Orange]

Ah so that's the LIGO the scientist (Scott Ransom) referenced in that podcast.  He said they were considered more likely to be successful than his experiment but you never know.  His way is discussed here: http://nanograv.org/.  Here's the gist:

Pulsars are rapidly rotating stars. A pulsar emits beams of radio waves which, like lighthouse beams, sweep through the sky as the pulsar rotates. The signal from a pulsar can be detected by radio telescopes as a series of regularly spaced pulses, essentially like the ticks of a clock. In fact, for the purposes of this experiment, it's useful to think of the pulsars as clocks. Gravitational waves affect the time it takes the pulses to travel from the pulsar to a telescope on Earth. We seek out perturbations due to gravitational waves in measurements of pulse arrival times at a telescope, in other words, we look for deviations in the clock ticks!

Thank you for the link. I would agree that the nanograv team will almost certainly be more successful than LIGO (Not sure if I linked to them before so here just to put it out there http://www.ligo.caltech.edu/). The weakness in this approach is the necessity for accurate timing measurements. They need to be able to observe a radio pulse in order to find gravitational waves. However this is the tried and tested approach, which we know will work, and was originally used to get Hulse and Taylor their Nobel prize.

However it is far from a direct detection of gravitational waves in the absence of any pulse, which is the goal of interferometric methods. LIGO probably doesn't have the sensitivity to detect gravitational waves on it's own but it can supply some important constraints on the backgrounds and noise we should expect. A much more successful approach will be LISA, if it is ever built (http://lisa.nasa.gov/). LISA is a space based interferometer that will be more sensitive and should be able to detect gravitational waves form their passing without the need to monitor received pulses from binary systems. That is when the search gets very interesting.

[jazmunda]

Hey science geeks. Are any of you guys able to identify this phenomena? The sun had a really cool rainbow ring around it today. I've never seen this before.

[Agent : Orange]

Hey science geeks. Are any of you guys able to identify this phenomena? The sun had a really cool rainbow ring around it today. I've never seen this before.

Sure, that's a nice picture of a 22-degree halo. It's made from a combination of both reflection and refraction of sunlight through ice crystals in the upper atmosphere. Each of those crystals is hexagonal and acts like a little prism floating in the air so you get light bent by a minimum of 22 degrees which is the typical angular size of that ring on the sky. You typically need a bit of cirrus cloud to get them, when the air is very calm the crystals are randomly oriented and you get the ring like shape. If you were to see the Sun closer to the horizon through this kind of cloud, the crystals are typically settled and they are more or less aligned vertically so you get preferential reflection and refraction in a horizontal plane and wind up with a phenomenon called Sun Dogs, which look like bright spots to the left and right of the Sun. With the Sun dogs and the halo both reflection and refraction are occurring so not only do you get a ring or other Sun mirages, you can also sometimes see a rainbow pattern in the ring with red light bent the least. So there's red on the inner part of the ring and a rainbow effect through it which is visible in your photo too. In the olden days people used to use these mirages as a weather forecasting device and the apparent omen is that it meant upcoming precipitation which might have a grain of truth to it considering you need both moisture in the atmosphere to make the ice crystals and cloud formation to produce light cirrus.
Anyway there are some more nice pictures that look just like yours here: http://earthsky.org/space/what-makes-a-halo-around-the-moon

[jazmunda]

Thanks AO.

I've seen a ring around the moon but never around the sun.

Oh and it rained in the afternoon.

[area51drone]

Now that Jazmunda has posted in this thread, expect a short death for it.  I'd give it, oh, about 6 weeks.

[zeebo]

Now that Jazmunda has posted in this thread, expect a short death for it.  I'd give it, oh, about 6 weeks.

Nah we need Jaz's perspective ... I think Australia has different physics.  Things go backwards and upside-down.  Plus the stars in the night sky are all weird.  Scientists are still trying to unravel it all.

[area51drone]

Nah we need Jaz's perspective ... I think Australia has different physics.  Things go backwards and upside-down.  Plus the stars in the night sky are all weird.  Scientists are still trying to unravel it all.

Exactly, he is the trough to our crest.   He cancels this thread out.

[West of the Rockies]

Well, at least the solar flares did not roast us all as a couple doomsayers predicted.

[steelbot]

Now that Jazmunda has posted in this thread, expect a short death for it.  I'd give it, oh, about 6 weeks.

Maybe 7, weeks...

[West of the Rockies]

Damn it, dude, you're jinxing it!  I posted yesterday specifically because I don't want this thread to go away.  It's one of the few spots where we aren't assaulted by political diatribes and forum user dust-ups!

[aldousburbank]

Well, at least the solar flares did not roast us all as a couple doomsayers predicted.

Damn!

[maureen]

Damn it, dude, you're jinxing it!  I posted yesterday specifically because I don't want this thread to go away.  It's one of the few spots where we aren't assaulted by political diatribes and forum user dust-ups!

I too appreciate the knowledgable posts and polite sanity. 

[zeebo]

Awesome new deep field pic from Hubble using gravitational lensing of giant galaxy cluster Abell 2744 to image galaxies as far as 12 billion light years away. 

The Hubble exposure reveals nearly 3,000 of these background galaxies interleaved with images of hundreds of foreground galaxies in the cluster. The many background galaxies would otherwise be invisible without the boost from gravitational lensing. Their images not only appear brighter, but also smeared, stretched, and duplicated across the field.  Thanks to the gravitational lensing phenomenon, the background galaxies are magnified to appear up to 10 to 20 times larger than they would normally appear. What's more, the faintest of these highly magnified objects have intrinsic brightnesses roughly 10 to 20 times fainter than any galaxies ever previously observed.

Full story here

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