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Bloggingheads 06-20-2009 02:43 AM

Science Saturday: The Recipe For Our Universe (Sean Carroll & Mark Trodden)
 

I'm SO awesome! 06-20-2009 10:16 AM

Re: Science Saturday: The Recipe For Our Universe
 
Booyah! Carroll's back, baby! I can't watch cuz I'm out of town but I can tell this talk is gonna be sweet. My favorite topics by the best commenter. Sean, I pre-ordered your book! Thanks for the setup, Bob.

bjkeefe 06-20-2009 01:10 PM

Re: Science Saturday: The Recipe For Our Universe
 
Great diavlog, I really enjoyed it. Some of it was over my head -- that's a good thing. I'll probably watch it again to see how much of that changes -- I did gain something a few times during the first listen by jumping back a couple of minutes and listening to a tricky part again.

One notion that seemed sort of obvious once I'd heard it, but had never thought about before, but in any case intrigued me, had to do with developing theories that "can't be tested." The plan/challenge is to develop a theory that makes (other) testable predictions that at the same time requires the untestable parts to be true as well, as a consequence of the overall theory. I really found that quite profound, for some reason.

Overall, I was surprised to hear how much new thinking appears to have been developed since I used to pay closer attention to this field. (Or maybe I was just kidding myself about how current I was ten and twenty years ago, and these guys are a better resource than what I had back then.)

Thanks again to Sean and Mark.

[Edited to remove opening complaint about sound balance. Turns out the problem was on my end, and having fixed it, I can confirm that there are no problems in the WMV file.]

Ocean 06-20-2009 01:40 PM

Re: Science Saturday: The Recipe For Our Universe
 
Great diavlog!

It seems like it's been a while since we had the particle physics/ cosmology talks that some of us enjoy so much. It's always good to hear some updates, even when the update is "we still don't know and may never be able to know" sort of thing. By the way, they said the LHC would be started later this year. What did ever happen to it last year? I thought that a cooling system had failed, but didn't know it would take this long to repair it.

A concrete question for Sean, Mark or any of the knowledgeable commenters is: what's the difference between working with Einstein's cosmological constant and working with the concept of dark energy? They said that by using the cosmological constant, there would be nothing in empty space, but I guess there would have to be some intrinsic property that can explain the constant. Can someone explain that?

Thanks!

JonIrenicus 06-20-2009 03:24 PM

Re: Science Saturday: The Recipe For Our Universe
 
So it seems that string theorists may be treated like some kind of carny folk within the physics community, is this sort of true?


I remember a physics professor I had awhile ago saying to the class if you ever attended some string theory talk as a student to raise your hand and ask the speaker - What is the Hamiltonian?

He said from him it would be considered snarky, but a student could pull it off.


I did have a question about particle physics in general though, is there any practical application to some of the new discoveries that may soon be made once the LHC goes online?

Particle physics seems to come across more as pure research than some other fields, which is fine by me.


I still do not get what dark matter is exactly,

************Enter LOTS of stupid questions*************


it seems strange if there is So much of it compared to normal matter that it would be so hard to detect it. At first I thought of it as sort of physical "chunks" of invisible stuff, something that you could hold in your hand, just not see.

But based on other reports it does not seem to cluster in chunks or does it? it is just sort of free floating particles of matter that interact very little with either normal matter or itself?


if a craft were to brush against an incredibly thick and dense band of dark matter (would that even be possible in how it exists?) would there be a normal type of reaction beyond a gravitational effect like the craft was brushing against say rocks? Or would it pass through the craft like some sort of ghost substance? It seems to be effected in the normal way by the gravitational force, but does it play by the same rules with say the electrostatic force?

Could it even be hard like rock? or gaseous? or is this nonsense talk as none of this applies to it?

nikkibong 06-20-2009 03:54 PM

Re: Science Saturday: The Recipe For Our Universe
 
Quote:

Originally Posted by JonIrenicus (Post 117171)
I did have a question about particle physics in general though, is there any practical application to some of the new discoveries that may soon be made once the LHC goes online?

That's a complicated question, which more or less boils down to this: we don't know. When US physicists were trying to stave off the cancellation of the Superconducting Supercollider in the early '90s, they made lots of outlandish claims regarding the possible practical applications of high-energy partical physics: it "might" cure cancer, it "might" have uses for medical diagnostics, it "might" . . . cure male-pattern baldness. Without actually having conducted much research though, it's quite impossible to tell. But it was hard (actually, impossible) to sell "knowledge for its own sake" as a reason for funding to the US congress, so people in the physics community had to resort to making these rather specious arguments.

On a pro SSC sheet they distributed to members of congress, the physicists appended the following quotation:

The story goes that, following a demonstration of the new miracle of electricity in 1831, Faraday was asked "What use is it?" He responded, "Sir, of what use is a newborn babe?"

Starwatcher162536 06-20-2009 05:07 PM

A few quick questions.
 
(.5A)Is there anyway to prove that we are not in the center of the universe with a linear redshift-distance law as opposed to being in the center with a quadratic redshift-distance law?

(A)I was under the impression, that since anything outside the Hubble radius is receding at values above c{z>C}, current theory is that the universe is still inflating, albeit much much slower then right after the Big Bang. Is dark energy what is suppose to be driving this inflation?

(B)If the above is true, then that means that a'(t) and a"(t) are >0, has this been measured? Is this why Hubble's constant is said to be decreasing? But doesn't this contradict the inflation model, since if a'(t) is increasing exponentially (like I would expect if the expansion depends on the volume of the universe) the constant should have a steady value, whats going on?

(B.5)Is there any difference between dark energy and zero point energy? If not, how can dark energy actually produce any effects? I thought the only reason you could subtract out the infinities of ground states is because only differences in energy are measurable. But since it is producing changes, does this mean the zero point energy is interacting with something outside our universe that has a even lower ground state?

(C)Since the Freidman equations depend on a isotropic universe (k can only have discrete values), what methods do we have to measure the receding velocities of distant objects that do not depend on the redshift?

Starwatcher162536 06-20-2009 05:20 PM

Re: Science Saturday: The Recipe For Our Universe
 
[disclaimer] Take everything I say with a grain of salt[/disclaimer]


Quote:

it seems strange if there is So much of it compared to normal matter that it would be so hard to detect it. At first I thought of it as sort of physical "chunks" of invisible stuff, something that you could hold in your hand, just not see.
Why do we see stuff? Because of electrons absorbing and remitting photons. Whatever the stuff is, I would bet it does not have electrons, or that for some reason, its electrons will only absorb wavelengths that don't exist anymore.

Quote:

But based on other reports it does not seem to cluster in chunks or does it? it is just sort of free floating particles of matter that interact very little with either normal matter or itself?
I think usually when you refer to something that is "Weakly Interacting", you just mean that is has no electric charge (Like Neutrinos for instance). This would fit in well with us not being able to detect it with light. It should clump together like everything else (I wonder if Paulis exclusion principle would apply to it...). I'm fairly sure the only reason we have a clue its out there is because it interacts with gravity normally.

I'm SO awesome! 06-20-2009 07:23 PM

Re: A few quick questions.
 
A) yeah, I'm pretty sure
B) I'm pretty sure the Hubble constant stays the same regardless of expansion
C) after searching I'd say probably the WMAP, light refraction or maybe postion of a galaxy in the sky compared to its last position but I don't really know and didn't search that hard.

Edit: after looking up my answer to B) I think I might be wrong. Sorry! Not
much help.

JonIrenicus 06-20-2009 08:00 PM

Re: Science Saturday: The Recipe For Our Universe
 
Quote:

Originally Posted by nikkibong (Post 117175)

On a pro SSC sheet they distributed to members of congress, the physicists appended the following quotation:

The story goes that, following a demonstration of the new miracle of electricity in 1831, Faraday was asked "What use is it?" He responded, "Sir, of what use is a newborn babe?"

I wish they had decided to fund the supercollider in the US instead of the ISS. The latter by comparison is virtually useless. And from what I recall from reports, the US version would have been even more powerful in terms of the energies involved. And it would have been nice to have that kind of lab in the US. Back in the late 90s when I was in high school I remember being so enthralled with the ISS, it was a SPACE station after all!

Too bad, having that kind of lab in the US would have been far more useful. I wonder how much more it would have cost, or would it have been cheaper than the ISS?

bjkeefe 06-20-2009 10:39 PM

Re: Science Saturday: The Recipe For Our Universe
 
Quote:

Originally Posted by Ocean (Post 117169)
By the way, they said the LHC would be started later this year. What did ever happen to it last year? I thought that a cooling system had failed, but didn't know it would take this long to repair it.

Some good explanations of why it was (would be) such a time-consuming repair starting here and here, and a little more about what they learned from the shutdown event here.

Ocean 06-20-2009 11:06 PM

Re: Science Saturday: The Recipe For Our Universe
 
Quote:

Originally Posted by bjkeefe (Post 117191)
Some good explanations of why it was (would be) such a time-consuming repair starting here and here, and a little more about what they learned from the shutdown event here.

Thanks! Very interesting indeed.

Starwatcher162536 06-21-2009 10:40 AM

Re: A few quick questions.
 
arghh, I have the feeling neither of our guests are going to check this thread and answer questions like Tim Maudlin did last Science Saturday.

bjkeefe 06-21-2009 10:43 AM

Re: A few quick questions.
 
Quote:

Originally Posted by Starwatcher162536 (Post 117209)
arghh, I have the feeling neither of our guests are going to check this thread and answer questions like Tim Maudlin did last Science Saturday.

Maybe you could post a comment over on Cosmic Variance asking Sean and/or Mark to check the forums. There are a couple of posts that mention this diavlog. Latest here.

(You could also ask your questions there, of course, but I can't in good conscience recommend that sort of treason.) ;^)

bjkeefe 06-21-2009 10:52 AM

Re: Science Saturday: The Recipe For Our Universe
 
Quote:

Originally Posted by JonIrenicus (Post 117171)
it seems strange if there is So much of it compared to normal matter that it would be so hard to detect it. At first I thought of it as sort of physical "chunks" of invisible stuff, something that you could hold in your hand, just not see.

But based on other reports it does not seem to cluster in chunks or does it? it is just sort of free floating particles of matter that interact very little with either normal matter or itself?


if a craft were to brush against an incredibly thick and dense band of dark matter (would that even be possible in how it exists?) would there be a normal type of reaction beyond a gravitational effect like the craft was brushing against say rocks? Or would it pass through the craft like some sort of ghost substance? It seems to be effected in the normal way by the gravitational force, but does it play by the same rules with say the electrostatic force?

Could it even be hard like rock? or gaseous? or is this nonsense talk as none of this applies to it?

Assuming you've already looked at Wikipedia's entry, you might also browse these search results: Cosmic Variance | Bad Astronomy.

Sorry I don't know the subject well enough to want to try to answer your questions directly.

I'm SO awesome! 06-21-2009 12:07 PM

Re: A few quick questions.
 
Yeah, sean typically answers questions in his blog but not here so that'd be your best bet. Also, there's a few high end physics forums around the web that have people who'll anwer immediately.

Starwatcher162536 06-21-2009 11:04 PM

Sean's Response
 
In case anyone else was interested.

Sean's Response:
Quote:



Starwatcher– If you believe we live in a special place in the universe, very strange distance/redshift relations are possible. There are some constraints, but as I recall (I may be out of date) they’re not very good.

Objects sufficiently far away are always moving faster than the speed of light, if the expanding universe is big enough. Dark energy is responsible for accelerated expansion: the apparent velocity of individual galaxies is increasing with time. “Inflation” refers specifically to accelerated expansion in the early universe.

Yes, we think that a’ and a” are both positive right now. That’s from real measurements. The Hubble parameter is a’/a, which is actually decreasing. although slowly.

Zero point energy is one possible example of dark energy. It produces effects through its influence on gravity (spacetime curvature). “Only differences in energy are observable” is not true once you include gravity.

It’s hard to measure velocities without using redshifts. You might look at Ned Wright’s tutorial for more info:

http://www.astro.ucla.edu/~wright/cosmolog.htm

bjkeefe 06-22-2009 03:47 AM

Re: Sean's Response
 
Quote:

Originally Posted by Starwatcher162536 (Post 117242)
In case anyone else was interested.

Sean's Response:

Yes. Thanks for passing it along.

rene 06-29-2009 08:01 AM

Re: Science Saturday: The Recipe For Our Universe
 
This was the most entertaining explanation I could find.

bjkeefe 06-29-2009 08:09 AM

Re: Science Saturday: The Recipe For Our Universe
 
Quote:

Originally Posted by rene (Post 118082)
This was the most entertaining explanation I could find.

Thanks for that, Rene. Entertaining and informative.

Ocean 06-29-2009 06:34 PM

Re: Science Saturday: The Recipe For Our Universe
 
Quote:

Originally Posted by rene (Post 118082)
This was the most entertaining explanation I could find.

Thanks! I'll watch it soon.

thouartgob 06-30-2009 04:03 PM

All pervading energy in vacuum
 
Besides residing in Bob new book maybe god just poked it's head out for a metaphysical chat :-)

Seriously enjoyed this diavlog and lamentably late in listening to it. Coming to this discussion after wading through the comments sections of late I wonder just how much "magic" resides in the secular halls of science. Not that I believe that there are any supernatural reasons behind the array of constants that when plugged into quantum theory allow those in the know to arrive at a highly accurate predictive mechanism ( sorry for the handwaving in my explanations ) but I wonder if there were to be a time when we are just left with a number(s) that cannot be derived from anything but answer what you want it to answer. What is the difference between that and god ? And would one of those numbers be 42 ??? ( sorry an easy joke )

Given the difficult nature of being able to measure accurately yet not be able to agree on what those measurements mean:

Other Interpretations of scripture

Can't we have a little more compassion for those of us who wonder at the unknowables behind the knowables ??


ps.
Weakly Interacting Bandwidth Excessive (WIBE) joke (not so easy joke )

ledocs 07-15-2009 12:32 PM

Re: Science Saturday: The Recipe For Our Universe (Sean Carroll & Mark Trodden)
 
I have made a series of negative critiques of diavlogs lately, but this one was great. I plan to record this at some point so I can return to it at will. This was bhtv worth watching.


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