1,465 research outputs found
What’s the problem with the cosmological constant?
The “Cosmological Constant Problem” (CCP) is widely considered a crisis in contemporary theoretical physics. Unfortunately, the search for its resolution is hampered by open disagreement about what is, strictly, the problem. This disagreement stems from the observation that the CCP is not a problem within any of our current theories, and nearly all of the details of those future theories for which the CCP could be made a problem are up for grabs. Given this state of affairs, I discuss how one ought to make sense of the role of the CCP in physics and generalize some lessons from it
Betting on future physics
The "Cosmological Constant Problem" (CCP) has historically been understood as describing a conflict between cosmological observations in the framework of general relativity (GR) and theoretical predictions from quantum field theory (QFT), which a future theory of quantum gravity ought to resolve. I argue that this view of the CCP is best understood in terms of a bet about future physics made on the basis of particular interpretational choices in GR and QFT respectively. Crucially, each of these choices must be taken as itself grounded in the success of the respective theory for this bet to be justified
Trans-Planckian Philosophy of Cosmology
I provide some philosophical groundwork for the recently proposed 'trans-Planckian censorship' conjecture in theoretical physics. In particular, I argue that early universe cosmology is, at least as we usually understand it, autonomous with regards to quantum gravity, the high energy physics that governs the Planck regime in our universe. Trans-Planckian censorship is then seen as a means of rendering this autonomy a novel empirical constraint within contemporary quantum gravity research
On efforts to decouple early universe cosmology and quantum gravity phenomenology
The Big Bang singularity in standard model cosmology suggests a program of
study in 'early universe' quantum gravity phenomenology. Inflation is usually
thought to undermine this program's prospects by means of a dynamical diluting
argument, but such a view has recently been disputed within inflationary
cosmology, in the form of a 'trans-Planckian censorship' conjecture. Meanwhile,
trans-Planckian censorship has been used outside of inflationary cosmology to
motivate alternative early universe scenarios that are tightly linked to
ongoing theorizing in quantum gravity. Against the resulting trend toward early
universe quantum gravity phenomenology within and without inflation, Ijjas and
Steindhardt suggest a further alternative: a 'generalized cosmic censorship'
principle. I contrast the generalized cosmic censorship principle with the
logic of its namesake, the cosmic censorship conjectures. I also remark on
foundational concerns in the effective field theory approach to cosmology
beyond the standard model, which would be based on that principle.Comment: A previous version of this paper misstated the scope of the intended
argument, and was subsequently withdrawn out of respect for those invested in
related areas of research. The present version resolves this issue, and also
includes a number of further revision
Empty space and the (positive) cosmological constant
I discuss empty space, as it appears in the physical foundations of
relativistic field theories and in the semiclassical study of isolated systems.
Of particular interest is the relationship between empirical measurements of
the cosmological constant and the question of appropriate representation of
empty space by spacetimes, or models of general relativity. Also considered is
a speculative move that shows up in one corner of quantum gravity research. In
pursuit of holographic quantum cosmology given a positive cosmological
constant, there is evidently some freedom available for theoretical physicists
to pick between two physically inequivalent spacetime representations of empty
space, moving forward: de Sitter spacetime or its 'elliptic' cousin.Comment: Final pre-print versio
Lorentz shift measurements in heavily irradiated silicon detectors in high magnetic fields
An external magnetic field exerts a Lorentz force on drifting electric
charges inside a silicon strip sensor and thus shifts the cluster position of
the collected charge. The shift can be related to the Lorentz angle which is
typically a few degrees for holes and a few tens of degrees for electrons in a
4 T magnetic field. The Lorentz angle depends upon magnetic field, electric
field inside the sensor and temperature. In this study the sensitivity to
radiation for fluences up to 10^16 n/cm^2 has been studied. The Lorentz shift
has been measured by inducing ionization with 670 nm red or 1070 nm infrared
laser beams injected into the back side of the irradiated silicon sensor
operated in magnetic fields up to 8 T. For holes the shift as a function of
radiation is increasing, while for electrons it is decreasing and even changes
sign. The fact that for irradiated sensors the Lorentz shift for electrons is
smaller than for holes, in contrast to the observations in non-irradiated
sensors, can be qualitatively explained by the structure of the electric field
in irradiated sensors.Comment: Accepted publication for RD09 conference in Proceedings of Scienc
Would Two Dimensions be World Enough for Spacetime?
We consider various curious features of general relativity, and relativistic
field theory, in two spacetime dimensions. In particular, we discuss: the
vanishing of the Einstein tensor; the failure of an initial-value formulation
for vacuum spacetimes; the status of singularity theorems; the non-existence of
a Newtonian limit; the status of the cosmological constant; and the character
of matter fields, including perfect fluids and electromagnetic fields. We
conclude with a discussion of what constrains our understanding of physics in
different dimensions.Comment: 31 pages, 1 figur
Priority and privilege in scientific discovery
The priority rule in science has been interpreted as a behavior regulator for the scientific community, which benefits society by adequately structuring the distribution of intellectual labor across pre-existing research programs. Further, it has been lauded as part of society's "grand reward scheme" because it fairly rewards people for the benefits they produce. But considerations about how news of scientific developments spreads throughout a scientific community at large suggest that the priority rule is something else entirely, which can disadvantage historically underrepresented or otherwise marginalized social groups
Priority and privilege in scientific discovery
The priority rule in science has been interpreted as a behavior regulator for the scientific community, which benefits society by adequately structuring the distribution of intellectual labor across pre-existing research programs. Further, it has been lauded as part of society's "grand reward scheme" because it fairly rewards people for the benefits they produce. But considerations about how news of scientific developments spreads throughout a scientific community at large suggest that the priority rule is something else entirely, which can disadvantage historically underrepresented or otherwise marginalized social groups
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