Gravity Definition and 1000 Threads

Basically, I'm a Physics/Math MSc student. Currently strengthening my background in Diff. Geo., QFT, GR. I feel like I should start reading some research papers on Quantum Gravity but I do not know where to start. What papers should I start with? I need papers that are accessible to 2nd year...

Classical gravity is additive. Therefore classical gravity obeys Gauss´ law. One result is absence of gravity in any hollow, spherically symmetric shell. In general relativity, gravity is not additive. Simple example is a black hole. The gravity of a classical point mass diverges to infinity...

if I apply a force constant F=100N en ##y## direction to a body of mass 2kg, it is elevated 3m and I know that the force of gravity is in ##y## direction too. What is the work that I did? I think: ##W_{me}=(F_{me}-F_{g})\times 3## it is correct? and the work made by gravity is "0".

The question is: The General Relativity Ideas were confirmed by the position of Mercury by Eddington. How could they be certain that the light deviation was due to gravity rather than the lens effect the Sun's corona may have had? What process was used,if any,to remove the effect of the...

"Gauss's theorem can be established as follows. consider an attracting particle of mass m at the point P, and let a cone of small solid angle ω be generated by radii through P. This cone cuts the surface at the points Q1, Q2, ... taken in order from P; the parts of the surface cut off by the...

I've just watched a vid about jets of matter and neutron stars. It was stated in it that a neutron star is a star that's been compressed from say a sun sized star to the size of a city, every thing OK upto now. Then it goes on to say that it has, the neutron star, enormous gravity, this is were...

At an L1 LaGrangian point between two bodies, one could - materials science notwithstanding - pit two of Newton's Laws (LM3,UG) against each other to provide thruster-free stationkeeping. Would it be feasible to use that to launch free from the system ? either spit out like a watermelon seed...

Homework Statement The Lagrangian density for the ##h=h^{00}## term of the Einstein gravity tensor can be simplified to: $$L=-\frac{1}{2}h\Box h + (M_p)^ah^2\Box h - (M_p)^b h T$$ The equations of motion following from this Lagrangian looks roughly like (I didn't calculate this, they are given...

Work in quantum foundations is partly considered important because of the hope that the way we think about QM may point to a road to quantum gravity. Lucien Hardy, who is well-known in quantum foundations for his reformulation of QM in terms of five "reasonable" axioms, is one of the people who...

How would the world be if light didn't travel in a straight line? I was wondering how it would affect life.

I am trying to answer a question about projectile motion were the change in height is that significant that the gravity cannot be assumed constant.

What is the physical property that gravity has that enables it to make an object go faster or, if it is resting on the ground, have weight? In General Relativity (as I understand it) objects in free fall move in geodesics. Thus an orbiting satellite moves in the curve around the planet that is...

What is the physical property that gravity has that enables it to make an object go faster or, if it is resting on the ground, have weight? That means it can do work: it gives objects kinetic energy. Where does that ability come from and where does the energy (the gravitational potential...

(This is to check my understanding ) I gather that gravity being a space-time distortion is thought to affect everything - mass, radiation, whatever - and can be thought of as an accelerational effect. If it is an acceleration, even entities with mass = 0 are accelerated (?). So is there any...

Hello, all - A question has come back to tickle my brain. Could a vehicle with less than 1G of thrust manage to escape the Earth's gravity well? I'm thinking something like Space X's Falcon 9. As it landed, with just a little more thrust, it could go back up again, I would guess. So, if it...

Homework Statement The distance between the centres of the Earth and the moon is 60 times the radius of the earth. Calculate the centripetal acceleration of the moon. Acceleration due to gravity on the Earth's surface is 10m/s. Homework Equations Centripetal acceleration= v^2/R Orbital...

Problem Statement From the top of the building if we throw one ball straight up with speed v and one ball straight down with the same speed v, then which ball has the greater speed when it reaches the ground? The attempt at a solution I think the ball which is first thrown straight up will...

I am building a rainwater collection system and want to know how much higher the tops of my PVC downspouts have to be compared to where the water exits into my rain tank. Or, how tall my rain tank can be if my downspouts are 10 feet tall. Let's say that the rain tank and home foundation are...

When a stream of water falls perfectly vertical, some water hitting the surface will disperse horizontally. What is the force that causes this? References would be awesome!

I'm trying to get a sense of the current state of knowledge regarding the relationship between gravity and quantum phenomena. For example, if you had a super-sensitive gravity detector, would that count as a "measurement" in the double-slit experiment in the same way that a particle detector...

I'm Dan. I'm trying a few theories out and came up with some pretty sweet stuff. I just want to let people know because its humanities right to know. I know its unlikely anyone will believe anything I put on here just because its human nature for people too. Good thing science isn't about belief!

I just had the thought that atoms emit light at quantized levels but that would seem to imply that only certain energy levels could possibly exist instead of a complete spectrum. But, if light is traveling down or away from a gravitational field the frequency gets shifted. Would this make it...

Commonly it is said that the gravitational field has 6 degrees of freedom (a symmetric tensor, that is 10, minus 4 conservation laws). But is this accepted without any dispute? The reason for my question are so called "indirectly coupling" models, where the primary gravitational field is...

Homework Statement I am trying to solve a problem that I have invented. It consists of a metal stick of mass m, which falls by the action of gravity (g=constant) within a perpendicular constant magnetic field B. The direction of magnetic fiel is showed in the image. The stick makes electrical...

They found an underground lake on Mars last week! Given that the lake exists and is actually liquid (and has a surface), two obvious questions come to mind: 1. Will I be able to beet my earthly current record in bouncing a pebble there? 2. If I release a pebble from a given height here and...

There's important experiments showing the equivalence of inertial mass and gravitational mass ( the Eotvos experiments), but I couldn't really find many that show the equivalence of mass (or the stress-energy tensor) in other contexts. These are some of the variants of mass I'm interested in...

Homework Statement h = 10 ft RHO = 10 ppg (or pounds/gallon) Homework Equations P = 0.052 * RHO * h P = RHO * G * h I am very confused right now as why each equation gives a different answer! What are the correct units for the 2nd equation and how do I convert from second equation to the...

Entropy is always increasing, say the thermodynamicists, and the increase will ultimately caue a "heat death" of the universe. But gravity seems to contradict this. Gravity, by clumping matter together, always engenders a decrease in entropy. Indeed, some cosmologists propose an eventual...

So, this is a bit of an odd question, but something I was curious about. I recently learned in layman's terms that the universe is considered flat because of how we measure triangles in 3D space, in particular the CMB. I've also learned that the cosmological constant that was derived from GR...

Is it possible that gravity affects time by constricting motion? We know that gravity can redshift light so if time is measured by the vibration of cesium atoms might it be similar to the effect of a pendulum being slowed by adding weight. That is the dilation of time is caused by the force of...

I am making this thread to discuss interesting open questions in Gravity and Cosmology with people working in these or even relevant area. Anyone who is working in these (and relevant) areas, please identify yourself here and we will begin and hopefully people will catch on and contribute.

At a high/abstract level, I'm trying to understand how QM treats gravity. What if you set up a Schrödinger's cat experiment so that the cat lost some of its mass when in the "dead" state. So, someone outside the box could "observe" the cat being alive or dead based on change in gravitational...

I'm would like to learn of the practicality of separating HHO gas released from a photovoltaic charged lead-acid battery bank for hydrogen storage, perhaps by exploiting the substantial difference in density of the two elemental gases. It occurred to me that were the gas emitted from batteries...

I'm currently doing my thesis in QG and there's a distinct gap between where QFT and GR left off and QG begins, and as I'm sure most of you know, in a thesis you're sort of just thrown right into the deep end. As such, I was hoping someone could recommend a decent textbook that gives a solid...

Newton's law of gravitation cannot be compatible with relativity because the gravity from a massive object applies a force to all other masses infinitely fast. General relativity is supposed to correct this flaw by setting a speed limit on how fast the effect of gravity can reach a distant...

Regarding dark matter, is it possible that at the quantum level there is some unknown property to gravity that is making it appear that there is this dark matter attracting normal mass but it's actually just that on a galactic scale gravity acts different than GR predicts? Or is that completely...

This 54 page review article from a September 2017 conference in Portugal is a good starting point for people wanting an overall summary of the state of BSM physics theories that is reasonably up to date, and may suggest questions about specific theories that deserve more attention in this forum...

Hello, I am trying to find out how to determine the center of gravity of a CubeSat present in an uniform sphere of radius R, using the initial data given by gyroscopes. The satelitte is equipped with magnetometers, gyroscopes, and accelerometers. By taking into account that the only values I...

If a celestial body's kinetic energy (say, the Moon's) surpassed the energy necessary to exceed the gravitational binding energy (GBE), would said body break apart because of it? For example, the Moon is currently orbiting the Earth at a speed of 1020 meters per second, giving it a kinetic...

This has been noodling in the back of my mind ever since I read about the field strength in magnetars etc. Magnetic fields store energy. Magnetic fields in magnetars are inconceivably large (~10^11T). This inconceivably large magnetic field contains ~4x10^27J/m3 From that famous guy whose...

For example, do electrons, atoms etc. experience gravity? Is this proved by experiment?

Suppose there are 2 planets the size (diameter) of Jupiter. Both have the exact same mass. They are separated by a distance of about 10 times the diameter of the planet. They are both at rest. Now, will they start moving towards each other or stay in the same place? This is a sort of thought...

What would be the value of gravity on the surface of the Earth if its mass was twice as large and its radius half of what it is now?

When a force follows the inverse square law, its effects are stronger as the source approaches than when it recedes. So light will blue shift (higher energy) and sound is louder and at a higher pitch. So I would think that gravity would be stronger from an approaching object that from a...

Hi I have 2 questions. There are 2 planets and one clock on each of them. One of them has a bigger gravitational field strength. And two clock have same distance from the core. 1-) Does time dilation occur between two? Which clock ticks slower? 2-) If time dilation occurs, which formula...

How do the components of the stress-energy tensor act on gravity regarding a) the FRW-universe? b) a solid ball? In a FRW-universe ##\rho + 3P## determines the second derivative of the scale factor. So, there are no non-diagonal components. Just theoretically, if the perfect fluid was...

Hi, I am working on a video, and I was wondering if any of you knew of some real-life demonstrations I can do about black holes? So far I have the gravity well, and the balloon covered by foil that you crush to show same mass but denser. My video is about the anatomy of a black hole, so I cover...

Hello, I have a question regarding Damped Harmonic Motion and I was wondering if anyone out there could help me out? Under normal conditions, gravity will not have an affect on a damped spring oscillator that goes up and down. Gravity will just change the offset, and the normal force equation...

As I understand it, Newton considered the influence of gravity between two objects to be instantaneous. Now it would appear that gravity has a speed limit. If the Earth is influenced by the sun from where it was 8 minutes ago, how does the Earth keep up with a traveling sun? Does relativity...

I am trying to compare an experiment on spinal changes due to zero-g in astronauts. Researchers simulated zero-g spinal elongation by suspending human subjects so that no part of their body touched the ground. This figure shows the % change in disc thickness for each subject compared to data...