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Relative Masses of 7-Billion-Year-Old Protons and Electrons Confirmed to Match Those of Today's Particles

The mass of the proton in relation to its much lighter counterpart, the electron, is known to great precision: the proton has 1836.152672 times the mass of the electron. But has it always been so?
Quite possibly, according to new research which taps the cosmos as a vast fundamental-physics laboratory. A study of a distant galaxy strongly suggests that the proton-to-electron mass ratio, denoted by the Greek letter mu (µ), has remained essentially constant for at least half the age of the universe. The findings appeared online December 13 in Science.

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Title: Constraining the variation of fundamental constants at z ~ 1.3 using 21-cm absorbers
Authors: H. Rahmani, R. Srianand, N. Gupta, P. Petitjean, P. Noterdaeme, D. Albornoz Vasquez

We present high resolution optical spectra obtained with the Ultraviolet and Visual Echelle Spectrograph (UVES) at the Very Large Telescope (VLT) and 21-cm absorption spectra obtained with the Giant Metrewave Radio Telescope (GMRT) and the Green Bank Telescope (GBT) of five quasars along the line of sight of which 21-cm absorption systems at 1.17 < z < 1.56 have been detected previously. We also present milliarcsec scale radio images of these quasars obtained with the Very Large Baseline Array (VLBA). We use the data on four of these systems to constrain the time variation of x = g_p*alpha^2/mu where g_p is the proton gyromagnetic factor, alpha is the fine structure constant, and mu is the proton-to-electron mass ratio. We carefully evaluate the systematic uncertainties in redshift measurements using cross-correlation analysis and repeated Voigt profile fitting. In two cases we also confirm our results by analysing optical spectra obtained with the Keck telescope. We find the weighted and the simple means of Delta_x / x to be respectively -(0.1 ±1.3)x10^-6 and (0.0 ±1.5)x10^-6 at the mean redshift of = 1.36 corresponding to a look back time of ~ 9 Gyr. This is the most stringent constraint ever obtained on Delta_x / x. If we only use the two systems towards quasars unresolved at milliarcsec scales, we get the simple mean of Delta_x / x = + (0.2 ±1.6)x10^-6. Assuming constancy of other constants we get Delta_alpha / alpha = (0.0 ±0.8)x10^-6 which is a factor of two better than the best constraints obtained so far using the Many Multiplet Method. On the other hand assuming alpha and g_p have not varied we derive Delta_mmu / mu = (0.0 ±1.5)x10^-6 which is again the best limit ever obtained on the variation of mu over this redshift range.

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Dimensionless cosmology
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Title: Dimensionless cosmology
Authors: Ali Narimani, Adam Moss, Douglas Scott

Although it is possible that some fundamental physical constants could vary in time, it is important to only consider dimensionless combinations, such as the fine structure constant or the equivalent coupling constant for gravity. Once all such dimensionless numbers have been given, then we can be sure that our cosmological picture is governed by the same physical laws as that of another civilization with an entirely different set of units. An additional feature of the standard model of cosmology raises an extra complication, namely that the epoch at which we live is a crucial part of the model. This can be defined by giving the value of any one of the evolving cosmological parameters. It takes some care to avoid inconsistent results for constraints on variable constants, which could be caused by effectively fixing more than one parameter today. We show examples of this effect by considering in some detail the physics of Big Bang nucleosynthesis, recombination and microwave background anisotropies, being careful to maintain dimensionlessness throughout. We also give a dimensionless version of the parameters of the standard cosmological model. Rigorously determining how to talk about the model in a way which avoids physical dimensions is a requirement for proceeding with a calculation to constrain time-varying fundamental constants.

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The European Science Foundations new EUROCORES (European Collaborative Research Scheme) programme EuroQUASAR - European Quantum Standards and Metrology - could lead to crucial developments in time-keeping and scientific measurement. The work may allow scientists to measure the effects of gravitational waves to go beyond Einstein's theories and gain new insights into quantum effects that will lead to quantum computers and communications. The programme will also pave the way for the most accurate optical clocks and inertial sensors ever made that will provide researchers with better than pinpoint accuracy in determinations of the fundamental physical constants of nature.

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Proton electron mass ratio
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According to a new study carried out at the Max Planck Institute for Radio Astronomy, the mass ratio between the electron and the proton remained constant over the past 6 billion years. This comes to contradict the findings of a study conducted nearly two years ago which suggested that the masses of the two particles varied significantly since the Big Bang event which is responsible for the birth of the universe.
There are some theories in physics implying that certain physical constants of the universe might have varied in time, including the masses of sub-atomic elementary particles. Finding out whether this is true or not may have significant implications on our understanding of the universe, its nature, if the speed of light varied as well or whether mysterious entities such as dark energy and extra hidden dimensions can exist.

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Don't take our starry skies for granted. If you were unlucky enough to be living in some other universe, you might have nothing to stare at but black holes.
At least, that's the view of a new study that examines the nature of other universes that might support life and suggests that our cosmic habitat is nothing special after all - wondrously starry skies apart.

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Fundamental Constants
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Title: Stars In Other Universes: Stellar structure with different fundamental constants
Authors: Fred C. Adams

Motivated by the possible existence of other universes, with possible variations in the laws of physics, this paper explores the parameter space of fundamental constants that allows for the existence of stars. To make this problem tractable, we develop a semi-analytical stellar structure model that allows for physical understanding of these stars with unconventional parameters, as well as a means to survey the relevant parameter space. In this work, the most important quantities that determine stellar properties -- and are allowed to vary -- are the gravitational constant $G$, the fine structure constant $\alpha$, and a composite parameter $C$ that determines nuclear reaction rates. Working within this model, we delineate the portion of parameter space that allows for the existence of stars. Our main finding is that a sizable fraction of the parameter space (roughly one fourth) provides the values necessary for stellar objects to operate through sustained nuclear fusion. As a result, the set of parameters necessary to support stars are not particularly rare. In addition, we briefly consider the possibility that unconventional stars (e.g., black holes, dark matter stars) play the role filled by stars in our universe and constrain the allowed parameter space.

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Different fundamental constants
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In a paper soon to be published in the Journal of Cosmology and Astroparticle Physics, astrophysicist Fred Adams says that the three most relevant physical constants that determine star formation can have very different values, yet still permit stars to appear. In other words, there is nothing obviously 'special' about their values in our Universe at all.

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Physical Constants in the Cosmos
Have the laws of physics stayed the same throughout the history of the cosmos? It’s an interesting question because even minute changes to physical constants could imply the existence of extra dimensions, of the sort posited by string theorists. But that’s a big ‘could’, because despite earlier controversial findings, at least one cornerstone constant — the ratio of a proton’s mass to that of an electron — looks to be exactly the same in a galaxy some 6 billion light years away as it is when we measure it on Earth. A study led by Michael Murphy (Swinburne University) presents the result in a recent issue of Science.

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The laws of nature are the same in the distant Universe as they are here on Earth, according to new research conducted by an international team of astronomers, including Christian Henkel from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn. Their research, published today in Science, shows that one of the most important numbers in physics theory, the proton-electron mass ratio, is almost exactly the same in a galaxy 6 billion light years away as it is in Earth's laboratories - approximately 1836.15.

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