Joseph Smidt

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  • July 7, 2010
  • 12:46 PM

Massive Early Stars And Molecular Hydrogen Cooling

by Joseph Smidt in The Eternal Universe

The big bang produced only Hydrogen and Helium with trace amounts of Lithium. (For the most part.)  This is a problem for star formation because stars need to be "cool" to form and typically you need heavier elements to help the star cool off.  This is why:

Gravity pulls mass together.  However, as matter gets pulled together it heats up and this heat causes the matter to want to expend again.  

... Read more »

  • January 5, 2011
  • 01:42 PM

How Physics Changes With F(R) Gravity.

by Joseph Smidt in The Eternal Universe

Einstein's general relativity rules the roost when it comes to gravity, but soon modifications to standard GR may detected on universal scales with new cosmological data. Fortunately, a realistic modified version of gravity, known as f(R) gravity, makes practical predictions that may be verified in the coming decades.

A recent paper by Motohashi, Starobinsky, and Yokoyama gives a good synopsis

... Read more »

Hayato Motohashi, Alexei A. Starobinsky, & Jun'ichi Yokoyama. (2011) f(R) Gravity and its Cosmological Implications. to be published. arXiv: 1101.0716v1

  • September 17, 2010
  • 12:49 PM

Cosmology Can Possibly Solve the Neutrino Hierarchy Problem.

by Joseph Smidt in The Eternal Universe

There are three neutrino species in the standard model, hereafter refereed to as 1, 2, and 3, that we know have mass from atmospheric and solar neutrino oscillation experiments. Furthermore, data from these experiments put constraints on the mass-splittings between these three neutrinos.  From atmospheric experiments we know the mass differences between 2 and 3 is |M223| ~ 1.4x10-3 eV2 and from

... Read more »

Jimenez, R., Kitching, T., Peña-Garay, C., & Verde, L. (2010) Can we measure the neutrino mass hierarchy in the sky?. Journal of Cosmology and Astroparticle Physics, 2010(05), 35-35. DOI: 10.1088/1475-7516/2010/05/035  

  • June 25, 2010
  • 01:05 PM

A Great History Of The Evidence For Dark Matter.

by Joseph Smidt in The Eternal Universe

In the paper Dark Matter: A Primer Garrett and Dudagives give a nice historical background to the accumulating evidence for dark matter.  Lets go through the history they lay out.

1.  J. H. Oort:  Astronomers have come to tust what is known as the mass to light ratio, M/L, that does a good job telling you what the mass of luminous matter should be based off of the luminosity of that matter.  

... Read more »

Katherine Garrett, & Gintaras Duda. (2010) Dark Matter: A Primer. Eprint. arXiv: 1006.2483v1

  • January 12, 2011
  • 12:31 PM

First Planck Results: The Sunyaev-Zeldovich Effect.

by Joseph Smidt in The Eternal Universe

There's been many bloggers writing about the first Planck results presented here at AAS and in Europe but I would like to write a little more than has been written on the Sunyeav-Zeldovich results as I think they are impressive.  Impressive both in terms of the science we get as well as well as this particular example shows how precise CMB experiments have become.  I will focus on the results

... Read more »

The Planck Collaboration. (2011) Planck Early Results: The all-sky Early Sunyaev-Zeldovich cluster sample. Submitted to A. arXiv: 1101.2024v1

  • September 10, 2010
  • 11:58 AM

Did Life Develop Shortly After Big Bang and Get Spread Throughout The Universe?

by Joseph Smidt in The Eternal Universe

I woke up to a very interesting paper by Gibson, Wickramasinghe, and Schild that appeared on the ArXiv last night and suggests that life most likely developed shortly after the big bang and was then spread throughout the universe.   They call this the biological big bang. (And at this point I should say that universe here means the "local universe" that was in casual contact between 2-8 million

... Read more »

Carl H. Gibson, N. Chandra Wickramasinghe, & Rudolph E. Schild. (2010) First life in primordial-planet oceans: the biological big bang. Submitted to International Journal of Astrobiology. arXiv: 1009.1760v1

  • January 28, 2011
  • 12:12 PM

Dark Matter Reconstruction From Radio Experiments.

by Joseph Smidt in The Eternal Universe

As photons move through the universe they get gravitationally lensed as the pass by large clumps of matter. (As shown in the image above.) Dark matter, being the dominant form of matter, lenses these photons more than anything.  Therefore, by studying the lensing properties of incoming photons, in principle we can reconstruct what the profiles of the dark matter doing that lensing.

Now, put (

... Read more »

Michael L. Brown, & Richard A. Battye. (2011) Mapping the dark matter with polarized radio surveys. E-Print. arXiv: 1101.5157v1

  • February 9, 2011
  • 01:03 PM

Current Cosmology From Supernova Data.

by Joseph Smidt in The Eternal Universe

Ariel Goobar and Bruno Leibundgu have recently submitted an article to Annual Review of Nuclear and Particle Science summing up our current understanding of physics from the current set of supernova data. We have accrued quite a lot of supernova data over the years and so it is interesting to take a look at how much we have learned. I will not report everything but will post a few interesting

... Read more »

Ariel Goobar, & Bruno Leibundgut. (2011) Supernova cosmology: legacy and future. To Appear In Annual Review of Nuclear and Particle Science. arXiv: 1102.1431v1

  • September 28, 2010
  • 01:23 PM

What Happens When A White Dwarf Collides With A Neutron Star?

by Joseph Smidt in The Eternal Universe

                             Image via WikipediaPaschalidis et al. recently simulated what will happen when a white dwarf collides with a neutron star in a head on collision incorporating the effects of general relativity.

In each case I will list the mass of the white dwarf and neutron star in solar masses, (meaning the mass of these objects after dividing my the mass of the sun) the ratio of

... Read more »

Vasileios Paschalidis, Zachariah Etienne, Yuk Tung Liu, & Stuart L. Shapiro. (2010) Head-on collisions of binary white dwarf--neutron stars: Simulations in full general relativity. Submitted to PRD. arXiv: 1009.4932v1

  • January 25, 2011
  • 01:00 PM

What If Dark Energy Were A Phantom Energy?

by Joseph Smidt in The Eternal Universe

Before we get too far ahead of ourselves, let's remember that dark energy being a cosmological constant fits the data very well and has for years. That said, experimental constraints allow for dark energy actually being an exotic form of phantom energy. (So for the time being we have to allow for the possibility and work out the details.) This was recently done by Dabrowski and Denkiewicz.


... Read more »

Mariusz P. Dabrowski, & Tomasz Denkiewicz. (2009) Exotic-singularity-driven dark energy. AIP Conference Proceedings. arXiv: 0910.0023v1

  • September 21, 2010
  • 12:07 PM

How To Possibly Detect Graviton Mass With Gravity Waves/Pulsars.

by Joseph Smidt in The Eternal Universe

Gravitons are the particles that mediate the force of gravity in the analogous way that photons are responsible for the electro-magnetic field.  And like photons, gravitons are thought to be massless.  In fact, assuming general relativity is correct, the mass of the graviton has an upper bound of 7x10-32 eV which is really small. (See bold text at bottom.)  However, for alternative gravity

... Read more »

Kejia Lee, Fredrick A. Jenet, Richard H. Price, Norbert Wex, & Michael Kramer. (2010) Detecting massive gravitons using pulsar timing arrays. Accepted by ApJ. arXiv: 1008.2561v2

  • September 22, 2010
  • 01:24 PM

How The Twin Paradox Of Relativity Changes In An Expanding Universe.

by Joseph Smidt in The Eternal Universe

I'm sure most of you have heard of the twin paradox "in which a twin makes a journey into space in a high-speed rocket and returns home to find he has aged less than his identical twin who stayed on Earth."  This paradox has been worked out for special relativity in Minkowski spacetime.  Recently, Boblest et al. worked out the details using general relativity for an expanding universe. (de Sitter

... Read more »

Sebastian Boblest, Thomas Müller, & Günter Wunner. (2010) Twin Paradox in de Sitter Spacetime. E-Print. arXiv: 1009.3427v1

  • August 18, 2010
  • 11:23 AM

Could The Planck Satellite Discover A New Species Of Neutrino?

by Joseph Smidt in The Eternal Universe

It has been known for some time that the WMAP data is more consistant with the existence of four neutrino species than three. Nevertheless, most cosmologists shrug this off as three is by no means ruled out. However, Hamann et al. 2010 demonstrate that such a dismissal may be a mistake.

It turns out, when WMAP 7 year data is combined with Sloan data, the three neutrino species model is ruled

... Read more »

Jan Hamann, Steen Hannestad, Georg G. Raffelt, Irene Tamborra, & Yvonne Y. Y. Wong. (2010) Cosmology seeking friendship with sterile neutrinos. Eprint. arXiv: 1006.5276v1

  • June 23, 2010
  • 01:18 AM

Does Ignoring Small Scale Physics Hurt Cosmology? Probably Not.

by Joseph Smidt in The Eternal Universe

When cosmologists study the universe they usually assume it is homogeneous and isotropic with linear perturbations.  On large scales this turns out to be a very good approximation.  Fortunately, these assumptions greatly simplify the math since:
The equations are linear and therefore easily solvable.
(Related to #1.)  Fourier modes decouple meaning you can solve for each mode independent of the

... Read more »

Daniel Baumann, Alberto Nicolis, Leonardo Senatore, & Matias Zaldarriaga. (2010) Cosmological Non-Linearities as an Effective Fluid. eprint. arXiv: 1004.2488v1

  • September 27, 2010
  • 12:15 PM

Distinguishing Our Universe From Other Similar Universes In The Multiverse.

by Joseph Smidt in The Eternal Universe

Srednicki and Hartle have raised an interesting concern recently about a limitation on the predictive power of multiverse theories. They observe that in multiverse theories, exact snapshots of our universe happen several times in different places. So if we want to have a physical theory that describes our universe, the one we live in, then the question arises: how can we tell which one it is from

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Srednicki, M., & Hartle, J. (2010) Science in a very large universe. Physical Review D, 81(12). DOI: 10.1103/PhysRevD.81.123524  

  • December 30, 2010
  • 12:11 PM

The Effects Of Special Relativity On Planetary Orbits.

by Joseph Smidt in The Eternal Universe

General relativity affects the orbits of planets in ways Newtonian gravity cannot account for. Interestingly, Lemmon and Mondragon explore if special relativity can account for the same behavior predicted by general relativity.   They find that qualitatively it can, but quantitatively it comes up a little short and so the full general relativistic treatment is still needed.

First a reminder: 

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Tyler J. Lemmon, & Antonio R. Mondragon. (2010) First-Order Special Relativistic Corrections to Kepler's Orbits. Submitted to American Journal of Physics. arXiv: 1012.5438v1

  • January 11, 2011
  • 03:40 PM

The Statistical Mechanics of Money

by Joseph Smidt in The Eternal Universe

Yesterday I listened to a talk by Victor Yakovenko of the University of Maryland about the physics of money and it was quite interesting. I think that after this talk I am finally beginning to understand economics while at the same time I suspect that most economists don't.

In his talk he said that back in 2000 he published a paper on how to apply statistical mechanics to free market economics.... Read more »

XI, N., DING, N., & WANG, Y. (2005) How required reserve ratio affects distribution and velocity of money☆. Physica A: Statistical Mechanics and its Applications, 357(3-4), 543-555. DOI: 10.1016/j.physa.2005.04.014  

  • September 7, 2010
  • 01:13 PM

Standard Cosmology Theory Is Confirmed By ACT For Smallest Scales In The Universe.

by Joseph Smidt in The Eternal Universe

It never ceases to amaze me how well standard cosmology theory fits the ever increasing amount of data with precision. The results just released from the Atacama Cosmology Telescope (ACT) confirm that, even on the smallest scales, the predictions of the Lambda CDM universe preceded by an epic of inflation are correct.  This study extracts data for L modes of The CMB between 500 and 10,000.  (For

... Read more »

  • October 31, 2011
  • 12:35 PM

Could The First Stars In The Universe Really Be Annihilating Dark Matter?

by Joseph Smidt in The Eternal Universe

Stars today burn bright through the interactions of elements like hydrogen and helium.  But was that the same story for the first stars in the universe, or was their light dominated by the annihilation of dark matter?  Recently,  Ili et al. took up the challenge of finding out what astronomers should be looking for if this is the cas.

Some background:  If dark matter really is a weakly interacting particle, then shortly after the big bang, when the un........ Read more »

Cosmin Ilie, Katherine Freese, Monica Valluri, Ilian T. Iliev, & Paul Shapiro. (2011) Observing Dark Stars with JWST. e-print. arXiv: 1110.6202v1

  • January 19, 2011
  • 12:14 PM

Evidence Against The Universe Being Fine Tuned For Life.

by Joseph Smidt in The Eternal Universe

Many people will tell you that the universe appears fine tuned for life.  Don Page has decided to address this issue scientifically by calculating the best value for the cosmological constant needed to support life in the universe and then comparing it to our own.  His conclusion is that the cosmological constant is actually an example that our universe is not fine tuned for life.


... Read more »

Don N. Page. (2011) Evidence Against Fine Tuning for Life. E-Print. arXiv: 1101.2444v1

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