3,818 reputation
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bio website physics.drexel.edu/~groenera/…
location Philadelphia, PA
age 27
visits member for 1 year, 3 months
seen 2 days ago

I'm a Ph.D. candidate in the field of Physics at Drexel University. My research interests include the formation and structure of dark matter in galaxy clusters and gravitational lensing.


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2d
reviewed Approve The role of gravity during planetesimal accretion
2d
comment Can it be inferred that our cosmological horizon has increased over time?
Lastly, welcome to the astronomy stack exchange :) This is probably not deserving of a separate comment, but feel free to inject strict definitions of the cosmological and particle horizons (for those of us who worry about them), or clarify the language in my above answer.
2d
reviewed No Action Needed Can A Black Hole Exist?
2d
reviewed Leave Open Can Jupiter's bands be made out using a 15x70 pair of binoculars?
2d
reviewed Approve Which galaxy is receding from the Milky Way the fastest? What is known of the mechanism behind its recession?
2d
comment Can it be inferred that our cosmological horizon has increased over time?
You also incorrectly interpret my first point. I am not saying the speed of light is a hard cut-off in what we can observe, however, I am saying that since the universe expands (in a non-trivial way), and the speed of light is finite, there is a fundamental limit to how far into the past we can see. In other words, it DOES have to do with the speed of light. Your definition of the particle horizon is a rather poor answer, since you fail to make it understandable in any way.
2d
comment Can it be inferred that our cosmological horizon has increased over time?
Firstly, I say "boring" because there weren't objects to look at in this stage of the history of the universe. People do study the swiss cheese universe at high redshift using radio surveys, but you are wrongly interpreting what I mean here, as stars and proto-galaxies have to have formed first - which is not what I am discussing here.
Dec
20
awarded  Custodian
Dec
20
reviewed Close How to find Schwarzchild radius and and parsec help?
Nov
2
reviewed Approve solar-eclipse tag wiki excerpt
Oct
30
awarded  Nice Answer
Oct
11
comment Which galaxy is receding from the Milky Way the fastest? What is known of the mechanism behind its recession?
There are a lot of unknowns about dark energy. However, typically, it is included into Einstein's field equations through the addition of a term called "the cosmological constant". If it is in fact supposed to be included in GR in this particular way (which it is absolutely not clear that it is supposed to be), then the interpretation is that it must have a negative equation of state. That's all I was saying below. Secondly, we have mapped out the large scale universe out to a fair distance - we do not live at the center of a void (unless the size of the void is that of the entire universe).
Sep
30
awarded  Explainer
Sep
24
awarded  Yearling
Jul
24
comment Could dark matter particles be unstable?
@Envite That is absolutely incorrect. Astronomer's do not define dark matter as cold gas, dust, or the like, which is simply unobservable.
Jul
24
comment Did we ever actually see the earth revolving around the sun? Is the geocentric model completely disproved?
Well, epi-cycles were introduced to correct for the retrograde motions of the plants in a geocentric model; they never really worked super well, and even if one could make them work mathematically, they represent really complicating and unphysical orbits... Not the best argument, but I thought it should be included here.
Jul
24
awarded  Custodian
Jul
2
awarded  Curious
May
26
revised Calculating Angular Distance
azimuthal coordinates is more appropriate
May
18
answered How to calculate right ascension of Greenwich?