Matter Definition and 1000 Threads

I have heard that perturbative quantum gravity calculation predicts an increase of constant G at large distances. So I simply wonder can this growth in G naturally explain the galaxy rotation velocity curve?

I was just recently listening to a radio program, where a scientist said that we cannot observe electrons visually, but know they exist from their effects. That got me wondering... What is the smallest piece of matter that we DO have the capability of seeing? And, also, how much of what...

I need some smart people to explain to me why this idea I have, doesn't work. It's impossible for me to believe others have not thought it, since it's so obvious. What if spacetime is slipping backwards at the black hole at the center of every galaxy? So like a helicopter with no rotar...

For my research on astrophysics for the summer, a professor gave me this assignment but I don't know where to start. The question is: What methods could be used to find the dark matter distribution around a galaxy's central black hole?

I am not a student, just a cosmology enthusiast. I have read many articles and books on the subject, but very often the level of these books is beyond my scope. Often, I have found, that very complex presentations can be presented in a way that casual enthusiasts can understand. So if anyone is...

How does matter be created from light? When a photon strikes a heavy nucleus, it disintegrates and produces a pair of an electron and a positron. Or Two photons are collided and an electron positron pair is produced. Which is true?

I'm not a physics student (chemistry instead), and know extremely little about relativity, so this might be a dumb question and would appreciate simple answers. I'm just curious about this. :) So there is dark matter, which I understand to be the matter that is not detected but needed to...

I just looked Physics graduate admission application guidelines on websites of various US and other International universities. There wasn't any mention of Extracurricular activities at all, unlike undergrad applications which use them as a crucial factor for admission decisions. Do they matter...

Hi, I've been struggling to find the answer to this questions, which are probably simple ones. Does it matter what order a resistor and LED ( or any component ) are in. For example: Vcc -----resistor------Led------gnd or Vcc ------led-------resistor------gnd Are they the same...

UPDATE: New Paper discussion starts here: https://www.physicsforums.com/threads/erik-verlindes-new-view-on-dark-matter.755235/#post-5615947 This is all I could gather from abstracts of talks and colloquiums he gave this year. Each of them have a different bit of information ******************...

$$\begin{equation} 0 = ({\rho}_m + P_m)u^{m}_iu^{m}_j + \frac{4}{3}{\rho}_ru^{r}_iu^{r}_j \end{equation}$$ where i,j = 1,2,3 and different. That is the off-diagonal elements of the tresstensor for matter fluid and radiation fluid. The energy conditions imply that ##\rho_m + p_m > 0## and...

I'll be cautious in asking my my question because I'm out of familiar territory. But... Given the following: that dark matter interacts with baryonic matter (exclusively?) via gravity, that evidence for dark matter shows that it exists largely near baryonic matter, and we are (almost?)...

There is now evidence dark matter fills what would otherwise be considered to be empty space. 'Cosmologists at Penn Weigh Cosmic Filaments and Voids' http://www.upenn.edu/pennnews/news/cosmologists-penn-weigh-cosmic-filaments-and-voids "Dark matter ... permeate[s] all the way to the...

A bunch of news sources are reporting that a group from the UK is working on a way to produce matter from light. As far as I was aware this was impossible so I assume that the news is getting it wrong again and/or sensationalising. But even in the abstract of the paper it's claimed that...

1) How much does it matter when getting a job? Would a student with a lower GPA that went to a more prestigious school be considered more than a student with a nearly perfect GPA going to a school that is not that great? 2) How much does it matter when applying to graduate school? For...

Hi. I've been looking into a possible career in physics once I graduate high school, and I was wondering which types of physicists study dark matter? I have heard astrophysicists do, but are there any others? Sorry if this question is in the wrong place, I've never posted anything before...

Ok, we have all read that space is expanding, especially in low mass areas between galaxies, as described by GR. And that mass bends space, like seen in gravitational lensing. My question is whether on larger scales and masses, like on the size of galaxies, space itself is warped? The properties...

Show that the experimental data are consistent with a Lande g factor of 2 for each of the ions by calculating the saturation magnetic moment. Explain what this means for Cr. I've calculated J using Hunds rules and have the equation M = gμJn, where M is the saturation magnetic moment. BUT...

I'm by no means a astrophysicists but I love reading, talking and studying all I can on the subject. I have a question on the original formation of dark matter. Could it be plausible that the formation of dark matter be the end result of the antimatter/matter collision right after the Big Bang...

Homework Statement For the problem see the attachment, I am trying to evaluate this integral... but the fun part is that I am getting totally different resultsThe Attempt at a Solution First of all, I tried to put the integral in the Mathematica, but the first result contained logarithms...

Today in my chemistry class, the teacher said: Is it true? If yes I have a doubt. 0 vloume means the matter will demolish right? Then how will the mass of the demolished matter be conserved according to Law of conservation of mass?

How is dark matter distributed (as far as we know)? Let's stay with a single galaxy like the Milky Way. I heard that dark matter is even more concentrated in the center than in the halo, that it is falling off when moving outside, but since the halo is so huge (how huge, ten times larger?)...

Hi all. I'm rather a novice in the realm of physics, aside from a class in high-school and my own independent interest. I often wonder if matter is infinitely divisible. What if it's possible to divide quarks, gluons, etc, we just don't have the methods? Does anyone have input on this...

Hello I have a question (well its 2 questions)... I'm not hugely knowledged on the subject so i tend to question things in a more ignorant way but i wanted to know two things: Firstly, how do astronomers weight a galaxy at an accurate level to be confident enough to say there is more stuff...

Hi, Why do photons not pass through matter like neutrinos since they have no charge. What are they interacting with when they are stopped by matter? Thanks, Elliott

In his popular cosmology book "Que faisiez-vous avant le Big Bang" (sorry, it doesn't seem to have been translated into English) Edgard Gunzig presents a scenario for spontaneous matter production by inflation whereby virtual particle-antiparticle pairs were separated by inflation too far apart...

I'm trying to get a basic understanding of the big bang in order to teach an advanced oceanography course to high school students this summer. The course starts with one lecture on the origins of the universe, solar system, the earth, and the ocean. I think I get the basics of BBT from quark...

From other threads here I’ve gained a rough understanding of why Dark Matter forms into a halo around galaxies. It makes sense, since DM doesn’t interact and doesn’t clump together, that when a DM particle falls from the halo towards the gravitational centre of the galaxy it gradually...

Does it matter if the resistor is on top or below a voltage source after doing a source transformation? According to this picture from wikipiedia, the resistor is on top of the voltage source: But even if the resistor (Z) was on the other side of the voltage source, it would still be...

I got into a top PHD institution for condensed matter physics. I already have a MS in physics doing condensed matter. Now after a few years of actual research, I'm not sure if condensed matter is for me anymore. I feel like a lot of condensed matter physics right now is just pressing a button on...

I have been following stories about dark matter and have, I think, a layman's grasp of it, to whit: In 1933 the Swiss astrophysicist Fritz Zwicky, who studied clusters of galaxies while working at the California Institute of Technology, made an inference similar to one previously made by Carl...

Hi all, I've been seeing this again and again, that delayed neutrons are the ones that are allowing thermal nuclear reactors to work etc. etc. What I do not understand is how are prompt neutrons controlled and how delayed ones are allowed to "do their thing" no problem ? Wiki says...

Could someone please clear this up for me. We have, Reflection (metal, mirror) Reflection (colour) Absorption (heat) Emission (heat) Transmission (glass) Sry but I use photoelectric effect to reference electrons absorbing photons of specific energies to be excited to higher energy levels, I...

Perhaps, this is an easy question, but still induces a lot of confusion to my self. I might not be the only one confused with the meaning of these concepts so it can help a ton to people, like me, confused with their meaning. So here is my confusion, Matter, as I researched it, although instead...

I'm hoping that David Horgan will create some supplemental material for this, as he has for several other LQG and CDT papers. The pedagogical supplements help one read and understand the papers. In any case, here's the recent deHaro paper AND the previous one that lays out the LQC matter bounce...

Hey all, I'm looking at my third year of university here, trying to narrow down what I want to do. As far as graduate schools, I'm pretty confident I can get into at least a low-tier school somewhere. I have a few publications and talks, and found out yesterday that I'm a Goldwater scholar as...

Let me start off by stating that I have no formal education in Astrophysics, or any other education beyond high school, so if my question is stupid, just say so! Dark Energy, from my understanding Dark Energy is used to explain the expansion of the universe, because when we look at distant...

All waves involve the transfer of energy without a net transfer of matter. What does 'net transfer of matter mean?':confused:

Disappointed with grades -- does it matter? I'm almost done with college and the grades I'm getting this quarter are not impressive. Looking through my transcript I realize that only a handful of times I ever got an A. Most of the time a B and quite a few times C or lower. What sucks is that I...

Homework Statement So this is more conceptual than anything. Say there is a wire loop on the x,y axis and a permanent bar magnet above it on the z axis. I understand according to Faraday's law that as the north end of the bar magnet moves towards the loop the magnetic flux is increasing...

Falling matter of supernova does "work" heating the core? A supernova core collapses and the rest of the star follows, inner layers arrive first, a shock wave wave forms? As outer layers continue to collapse and slow down is there a large radial time rate change in momentum as rapidly...

I'm looking primarily for answers from people who have been on admission committees or have otherwise reviewed applications from undergraduate students. When you look at a student's transcript, is the distribution of his/her grades a factor at all? For example, I performed only around average...

Primordial black holes as a dark matter candidate has been ruled out - http://www.nature.com/news/search-for-primordial-black-holes-called-off-1.14551

Closed, collapsing universe+only photons at first --> matter when hot? Suppose we had closed, collapsing universe with a uniform thermal distribution of low energy photons like that of the CMB and no other matter (I suppose we must pick the initial conditions right for collapse to occur) . As...

Hello, Grad school admissions are about over, and it looks like I will be choosing between UIUC, Cornell, or U Chicago for CME. I have research fellowships from Cornell and U Chicago, still waiting for financial details from UIUC. I'll visit UC and Cornell over spring break, but location...

Alright, I'm well aware of the law that energy/matter cannot be created nor destroyed, but: Considering that universe began at a certain point in time and didn't exist prior to that, doesn't there HAVE to be a mechanism that creates energy/matter? Without some way of creating something...

I have a Physic 201 understanding of physic. I understand that the most distant star (galaxy) that we can see from the Earth is 4.4 billion light years (the time of the big bang) away. I think this is called the viewing horizon. Assume a person on a planet 4.4 billion light years from...

If we consider a perfect relativistic fluid it has energy momentum tensor $$T^{\mu \nu} = (\rho + p) U^\mu U^\nu + p\eta^{\mu \nu} $$ where ##U^\mu## is the four-velocity field of the fluid. ##\partial_\mu T^{\mu \nu} = 0## then implies the relativistic continuity equation...

Hi all. Can anyone please recommend me a good undergraduate level Condensed Matter Physics book that has a number of examples and concise explanations rather than walls of texts? It should cover typical topics such as scattering, magnetism etc. I apologize if this may strike a nerve with...

Hello, I'm having trouble understanding why if there are dark matter particles and other such particles (neutrinos) streaming through the Earth at all times, why don't they just collide with the atoms in our body or the desk or what have you? I understand that they're probably "weakly...