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24 views

Is it possible that the acceleration of the growth of our universe is driven by the overall gravitational pull of neighboring universes [closed]

I am painfully unequipped when I think about my my knowledge of physics. Still, I am enthralled, as many of us are, by the mysteries and complexity of the universe, both known and unknown. I was ...
1
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1answer
57 views

Are objects repelled by the cosmological horizon in Lambda-CDM cosmology?

When an observer watches a distant object, is there a gravitational influence of the horizon on that object? ("Distant" here is meant to mean: at a distance that is a sizeable fraction of the Hubble ...
1
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1answer
43 views

Gravity and dark energy in space

I've been studying astrophysics and I read that our universe is still expanding because the gravity is not enough compared to the dark energy present. And right now we are not sure whether are ...
-1
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1answer
46 views

Could a large amount of antimatter accelerate the universe instead of dark energy? [closed]

It is not known whether antimatter is repulsed by or attracted to matter. For the purpose of this question, I assume that antimatter is repulsive to regular matter (otherwise this question makes no ...
-5
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1answer
40 views

Could gravitational waves give an illusion of an expanding universe? [closed]

‪Could the effect of “expanding” gravity (gravitational waves spreading at the speed of light) as it travels through space (and therefore becomes less local) red-shift all EM waves and thus give us ...
1
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1answer
136 views

Zero-energy universe - What is nothing?

I am a layman, so excuse me in advance for the stupidity of my questions, and I hope you can answer them in a way that I can understand. I have read, here and there, that the Universe might have a ...
1
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1answer
160 views

Why is the heat death, rather than a Big Crunch, the most accepted theory of the ultimate fate of the Universe?

The Heat Death is accepted by most as the end of the Universe, but how can that be? Wouldn't the Big Crunch make a lot more sense? I mean, even if everything in the Universe is spread out uniformly ...
1
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1answer
76 views

Modification of Gravitational force's law and related problem

I'm facing a problem which states the following: Suppose that it is discovered that Newton's law of gravitation is incorrect and that the force $F$ on test particle of mass $m$ due to a body of ...
-1
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1answer
72 views

Does space expansion increase potential energy, and hence increase mass?

As space expands the gravitational potential Energy increases. So does the potential energy between Atoms and quarks and so on. I have read several times that these effects are so minuscule that they ...
0
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1answer
66 views

Is this how vacuum works?

Vacuum exerts a net zero force, or i guess pressure? on what's inside it, right? So if the universe is expanding at an accelerating rate, is the vacuum of outer space is growing? Like space is ...
3
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2answers
302 views

“Dark Matter” vs. “Dark Spin”

I am rephrasing an answer to another PSE question as an new question here. Dark matter is invoked to explain the 'observed space-time geometry that does not match with predictions'. According to the ...
0
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2answers
52 views

Is it possible to survive the destruction of a planet (earth)? [closed]

I recently watched Star Trek VI: The Undiscovered Country again. The main story evolves around the destruction of a moon of the klingon empire which is their main ...
0
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1answer
171 views

What is the definition of gravitational horizon $R_h$ in the $R_h=ct $ universe?

Melia's $R_h=ct $ universe proposal suggests that our gravitational horizon $R_h(t)$ should be equal to $ct$ for all cosmic time $t$, not just its present value $t_0$: "several unpalatable ...
1
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0answers
56 views

If dark energy disappeared today, what would be the largest gravitationally bound structures in the universe?

In particular, what would be the largest gravitationally bound structure containing the milky way? As a bonus, how does this compare to the largest gravitationally bound structures assuming a ...
0
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2answers
204 views

Will everything eventually be a single black hole? [duplicate]

Given the idea that gravity is always a factor (even though greater distances are excessively tiny), would everything eventually end up forming a single black hole? My thinking is that, with infinite ...
1
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2answers
112 views

Confusion regarding the concepts and derivation of Hydrostatic Equilibrium for a star

First and foremost I am sorry for this; in order to make the questions clear I must first upload the lecture notes from my institution $^\zeta$ for the derivation of Hydrostatic Equilibrium: $^\...
0
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2answers
67 views

Is the universe expanding?

If spacetime is curved by object with mass, just like the sun curves space time and so makes the planets orbit around it and will eventually in time make them crash towards it then shouldn't the ...
2
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0answers
146 views

How could the universe's expansion “remove the mean gravitational potential”?

I'm citing W. C. Saslaw's The Distribution of the Galaxies: Gravitational Clustering in Cosmology, chapter 25, where he adresses (what seems to be a Newtonian approximation of) the thermodynamic ...
2
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2answers
182 views

Is Einstein’s general relativity applicable to early universe?

The Lagrangian of general relativity is linear (first order) in Riemann curvature. The cosmological term, if included, is zero order in Riemann curvature. From an effective field theory point of ...
4
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4answers
141 views

Applicability of time-dependent metric for expanding universe

What makes us believe that a time-dependent metric is the right way to describe expanding universe instead of just claiming that galaxies fly away from each other? I can see, that it allows them to ...
-2
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1answer
143 views

Could dark energy and gravity be explained as same phenomenon?

I have watched VSouce video on gravity. The idea is that gravity pulling it is just lots of mass bending space-time, and natural direction of movement becomes moving towards the mass, and since we ...
3
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0answers
53 views

Metric vs coframe energy-momentum tensor in metric-affine gravity

Conventions Latin indices represent components in the anholonomic frame and greek ones are for coordinate components. I will call $R_{\mu \nu} := R_{\mu \rho \nu}{}^{\rho}$ (Ricci tensor) and $\bar{R}...
2
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1answer
84 views

Isn't A Singularity Inevitable Given Infinite Time?

I am not a physicist but this is a question I've been trying to find the answer to for years and no answer I've been given has satisfied me. It's my understanding that gravity affects all matter all ...
2
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1answer
157 views

Why doesn't the universe collapse under its own gravity?

Is the reason the universe doesn't collapse into itself due to gravity because there is an infinite amount of bodies in infinite space, therefore there is an infinite amount of gravitational pull on ...
3
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1answer
129 views

How much uncertainty has the relic graviton background?

In the paper [1], it is mentioned that inflation predicts that a relic graviton background is about 0.9 K (cf. cosmic neutrino background, 1.945 K, and cosmic microwave background, 2.73 K). How much ...
3
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1answer
51 views

Cosmological constant phase transition?

I recently watched at a talk by Cumrum Vafa in which he stated that the cosmological constant allows us to define a time-scale $T_\Lambda=1/\sqrt{E_\Lambda}$. The time scale of this time is about 10¹¹ ...
3
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1answer
289 views

If the Big Bang theory is true, what caused it to explode?

According to the Big Bang theory, all the matter in the universe was amassed together at one single point. If this was the case, why was it able to explode? The density of the mass would create a ...
0
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0answers
60 views

Is there evidence the great attractor isn't just gravitationally lensed gravity?

Is there any evidence that the great attractor isn't just gravitationally lensed gravity? It seems odd that it would be directly on the other side of the black hole at the center of our galaxy and ...
0
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1answer
99 views

According to Newton's Law of Universal Gravitation, why isn't the universe shrinking? [duplicate]

Every point mass is attracted to each other with a force $F= \frac{GMm}{r^2}$. I know nothing about theories behind expanding universes but, why wouldn't the universe eventually shrink down to a ...
1
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1answer
54 views

Would “gravity” and the “law of gravity” have a meaning in a universe without matter?

I was discussing the fact that if there was no matter in the universe, just vacuum and radiation, can we say that anything called gravity wouldn't exist? In that universe, the Friedman equations ...
2
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1answer
78 views

Hubble bubble and the shell theorem?

According to the Hubble bubble theory a local void could explain deviations of the Hubble constant for measurements in close vicinity to out local group compared to the global Hubble constant and ...
2
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1answer
117 views

Dicke's variable speed of light proposal and his refractive index formula

As far as I understand Wikipedia, Robert Dicke in 1957 proposed a flat spacetime with a variable speed of light such that gravity works similar to a refractive index, slowing down the speed of light. ...
1
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1answer
273 views

Does the cosmological constant represent anti-gravity? [duplicate]

Does the cosmological constant represent anti-gravity? According to the current Lambda-CDM cosmological model, there must be a fair amount of the dark energy in the universe responsible for the ...
2
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0answers
124 views

How does dark matter distribution help to identify it's composition

A question regarding this recently released data, and the paper https://arxiv.org/abs/1708.01538 that details it's distribution: Abstract: We use 26 million galaxies from the Dark Energy Survey (...
3
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3answers
488 views

Is there 'gravitational force of repulsion'?

According to hubble's law of universal expansion, the velocity of a galaxy moving away from ours is directly proportional to the distance between the two. Now velocity is increasing in direction away ...
-2
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1answer
82 views

Red shift and the expanding universe pertaining to gravity wells

is it possible that gravity's effect on the energy level of light could be causing the red shift in light arriving from other galaxies and not an expanding universe? it is impossible, after all, to ...
-4
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1answer
87 views

Are far objects really accelerating away at that huge rate? [duplicate]

Discutssions around this question Why is light bent but not accelerated? got me thinking. Specifically, hsinghal said "The absorption lines appeared to be red shifted (de accelerated photons) they ...
-1
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3answers
61 views

Is the gravitational pull of the early ($10^{10}$ more massive) universe still observable?

During one of the early epochs of the universe it used to be 10^10 times more massive than it is now, just before the matter / antimatter annihilation. So what cosmic gravity is being asserted on the ...
0
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1answer
203 views

Can a photon attract another photon? [duplicate]

Now since Photons have energy too, is it possible for these particles to gravitationally attract each other.
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0answers
89 views

Expansion of Homogeneous Universe using Fluid Dynamics

In the MIT OCW course The Early Universe Prof. Alan Guth justifies the use of Newtonian gravity to approximately describe the homogeneous expansion of the universe, (at least a matter dominated one) ...
0
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1answer
413 views

Anti de Sitter and FLRW metrics

Perhaps this is a naive question, but I have been reading about conformal invariance and conformally related metrics and I would like to know if someone can clarify me some concepts on this. Anti de ...
1
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2answers
633 views

Is this a reasonable explanation for “the universe is finite but unbounded” which seems to be contradictory at first sight? [closed]

[Editorial note: I'm going to revise this question according to the suggestions made in comments and answers during the next few days. Thank you all for your valuable hints.] There's the "ant on a ...
4
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3answers
157 views

Current constraints on Dark Matter self-interaction from galactic profiles

The self-interaction of dark matter may be small but it cannot be negligible if it is able to dissipate energy to relax into galactic clumps (necessary to explain galaxy rotation curves). According ...
8
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2answers
922 views

Dark Matter vs Modified Gravity

Why do cosmologists and astrophysicists assume that the reason for the higher velocities of outer stars in galaxies is due to matter at all? The name dark matter seems misleading. Couldn't gravity ...
1
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0answers
60 views

As space-time expands between two stars, what happens to the gravitational potential energy seemingly lost as U~1/r => ZERO.?

As the space-time between two stars grows (the accelerating expansion of the universe) the gravitational potential energy between two stars is reduced as 1/r -> ZERO (r is the distance between stars). ...
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1answer
63 views

Universe expansion, sub-luminal velocity elements? [closed]

It's not another question about the mechanism of expansion velocity exceeding c Much literature is devoted to describing the expansion of the universe measured by Hubble's Law - how the speed of ...
1
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1answer
93 views

Universe expansion / contraction ambiguity

I've read everywhere that the universe is expanding, and accelerating the expansion. But it is our single point observations of the universe enough to resolve this result? What gives us 100% ...
1
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2answers
95 views

Where are the Gravitational effects of an Inifite Universe?

The Baryon Oscillation Spectroscopic Survey (BOSS) announced that BOSS has measured the scale of the universe to an accuracy of one percent. http://newscenter.lbl.gov/2014/01/08/boss-one-percent/ In ...
0
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1answer
91 views

Potential Distant Future Reversal of Universe's Dark Energy Scalars?

Assuming the most probable universe topology/parameterization -- a infinite flat / open universe following the Lambda-CDM model -- and most possibilities postulated on the long term evolution of such ...
1
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2answers
157 views

Velocities of galaxies as they move away from each other

I am currently reading A Universe from Nothing, by Lawrence M. Krauss, and I have come across a concept that I found confusing: Now, if gravity is an attractive force, then it should be slowing the ...