Something omitted in the Mailbag topic for 2/18 was the Cosmological Constant. That leftover omega of 0.7 is no longer just the pipe dream of theorists wanting a less messy universe, it seems to be filled up by the Cosmological Constant. Studies of supernovae in the past two years indicate that the expansion of the universe is accelerating in a way consistent with a lambda (the variable for the CosCons) that gives you that extra 0.7 in your Omega.
Background for those totally lost. Back when Einstein did his work in general relativity, the equations predicted an expanding universe. But, at the time, no one thought the universe expanded, so he tossed in a constant to keep things static. Later he regretted this, since the universe DOES expand, and he lived to see the proof. However, if you use a different value of lambda than the one Einstein used, you can get not only an expanding universe, but one that’s expanding faster every day. And that value just happens to also give us a “flat” universe.
Dave Van Domelen, stopped taking astrophysics courses just before the whole CosCons thing came back up, d'oh....
You know, I read just recently (I think it was this month’s Scientific American) that there is missing matter that they’ve been looking for, and they may have an answer.
Somebody somewhere thinks there are a lot more black holes than previously thought, and that would account for all the mass that must be there to account for how gravity’s working.
You are welcome for this valuable, thorough, specific, and verifiable input.
Dvandom, that was a great post. Wish you’d do it more often. (2 posts since October. WOW!)
After I do a little more internet sleuthing, I hope I’ll be able to find an online reference to an intriguing, far-out theory I read in the Dallas Morning News while I was back home visiting the folks back in December and January. In summary, “dark matter” may not exist at all, but we see gravitational evidence of more matter nonetheless. How to explain it?
We may be detecting the gravitational influence of other dimensions. Electro-magnetic energy (light, radio waves, etc.) cannot travel from one dimension to another, which is why other dimensions are invisible. But gravity can travel inter-dimensionally, according to the math, so so physicist Joe Lykken of Fermilab has offered this radical explanation for “dark matter.”
In other words, this matter is “dark” because it exists in another dimension where it cannot and never will be seen, but its gravity has an influence on our dimension all the same.
Other names mentioned in the article who support Lykken’s idea are:
Savas Dimopolous of Stanford, who suggests that the early, chaotic universe burst forth from a hidden dimension during a period of rapid expansion and organized itself into a series of neatly arranged, parallel folds. We live in one of these folds. Light cannot travel from one fold to another, so those folds remain forever hidden. These folds are also called “branes,” as in membranes. Since our universe is three-dimensional, it’s called a “three-brane”.
Lisa Randall, of Princeton and MIT, and Raman Sundrum Of Boston U., together recently “published papers describing mathematically a possible infinite fifth dimension beyond the four known dimensions of space and time.” These papers were published in the December 6 issue of Physical Review Letters.
Dimopolous and Randall have shown that this scenario might explain why gravity is so much weaker than electromagnetism.
This is what I gleaned from this article. I hope it’s on the web somewhere, but I haven’t found it yet. I hope it’s there so y’all can read it all and evaluate it.
I thought that “missing mass” was a reference to the dark matter problem. Essentially the problem is the discrepancy noted between various ways of measuring the mass in the universe. Karen mentions this discrepancy. Using the galactic velocities and calculating the required mass to hold the galaxies together gives a substantially larger amount of mass than calculating the mass of all the luminous objects. Thus the discrepancy is “missing mass”, also called dark matter, since it (as I just said) isn’t luminous.
I have seen comments describing this as “missing matter”, and going on to discuss how dark matter must be non-baryonic. I tried looking at some references, like Ned Wright’s Cosmology Tutorial: http://www.astro.ucla.edu/~wright/cosmolog.htm . What I saw talking about dark matter was in agreement with Karen, except it didn’t discuss “missing matter” in those words. I was trying to find a reference that did use those words, but was unsuccessful.
What’s a brane?
Jab1’s hypothesis has several problems, including: astrophysicists have searched not only using lumininence (sorry if that’s not the right spelling, but it’s late), but also gravitational effects. So if there were some mass in some other “dimension” (and this is a rather poor use of the word “dimension”), if would be detected.
Currently, mass is defined in terms of the amount of gravity it exerts. If you postulate that gravity is of varying strengths, that would require an entirely new definition of “mass”.
As for the article: what’s this about neutrinos not having mass? I’m a bit confused because in older physics books, “mass” was used to refer to total energy, while “rest mass” refers to the amount of energy at rest. Apparently there is a new trend to use “mass” to refer to what used to be known as “rest mass”. So when physicists say that they are trying to figure out whether neutrinos have mass, do they mean rest mass, or mass in the old sense?
if gravity is an active distortion of space–i.e., space itself is being sucked into gravity wells (implied by einstein’s math)–then space is a medium–a stuff–but it’s not matter, although matter exists in it and affects it. we know about matter & the things that affect matter–we don’t know much about this underlying “stuff”, space.
oooohhh, spooky!<font color=#950000">
A new world order has been formed/between the cheque book and the dawn/A new renaissance man is born"
Jim Moginie/Peter Garrett/Martin Rotsey(Midnight Oil), “Renaissance Man”
weird, huh? </font>
anyway, since gravity, though induced by mass, is actually a feature of space, it may be affected by things we know nothing about, because matter (like what we see as “us”) isn’t affected by those things.
hmmmmmmmmmmmmmmmmmmmm…
Okay, this is what I get for being in a hurry and not taking the time to fully quote from the articles I read. And Ryan, I get the feeling you didn’t fully read my post. I thought I made it clear that it wasn’t my hypothesis, it’s one made by Joe Lykken of Fermilab ( lykken@fnal.gov ) in Illinois.
As for the idea that gravity isn’t the same strength everywhere, that’s the theory of Lisa Randall of Princeton and MIT, along with Raman Sundrum of Boston U. You can read their paper here: http://focus.aps.org/v4/st28.html The paper is no longer than one of Cecil’s columns, so you should be able to read it in two or three minutes. This paper describes what a brane is. An abstract of a lecture entitled “Supersymmetry Breaking from Higher Dimensions” given by Randall at CWRU in Cleveland is here: http://erebus.phys.cwru.edu/~trodden/seminars/randall_abs.html Finally, a recording of a lecture given by Randall entitled “Do We Live in Five Dimensions?” is here: http://online.itp.ucsb.edu/online/bblunch/randall/ (hope you have RealAudio). Lastly, Randall’s email address is: randall@baxter.mit.edu I give their emails here in case you have questions for them, though I know getting a response from such busy people is a longshot.
Lastly, from the January 3rd Dallas Morning News article:
If you need more info, Ryan, I could Xerox a copy of this article and mail it to you. If it wasn’t a violation of copyright laws, I’d gladly post the entire article here. Not being a physicist, I post this stuff to see if there are any problems with it. You seem to know it better than I.
I just happened to be reading up on this stuff while the board was down.
The Ryan asked:
So when physicists say that they are trying to figure out whether neutrinos have mass, do they mean rest mass, or mass in the old sense?
The New York Times ran an article yesterday (2/29), which covered a speech wherein Dr. Katherine Freese said the dark matter, whatever it is, is nonbaryonic (that is, not normal stuff like protons and neutrons).
Most of the universe’s mass is ‘not normal’ stuff.
Well, it depends on what you’re looking for in dark matter. If you’re just worried about galactic dark matter, then sure, it could be all or mostly baryonic. It’s certain that at least some of it is-- last estimates I saw were that at least 20% of the galactic dark matter is MACHOs, presumably brown dwarfs and Jupiters. As to the cosmological dark matter, baryonic matter must again be some of it, but there can’t be enough baryonic matter to account for all of it. This doesn’t seem to present much problem anymore, as the evidence is increasingly pointing towards the Cosmological Constant exactly making up the difference (as Dvandom pointed out), so by Occam’s Razor, we needn’t postulate unobservable other worlds gravitationally bound to our own. Finally, a better question that “why is gravity so much stronger than electromagnetism?” is, “why do most particles have charge so much higher than their mass?”. Just my .16 bit.
“There are only two things that are infinite: The Universe, and human stupidity-- and I’m not sure about the Universe”
–A. Einstein
