Questions tagged [cosmological-constant]

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1answer
586 views

Constant term in Lagrangian

Why can we always drop any constant term in a Lagrangian density in quantum field theory? This issue is somehow related to the constant term being some kind of cosmological constant. Can you please ...
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2answers
318 views

Mutiple Zero Point Fields and the Cosmological Constant

Duality of elementary particles like electrons or photons is well known if not fully understood. There is ample research suggesting elementary particles are simply high energy states of universal ...
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3answers
371 views

Regardless of the multiverse. How are our constants and laws communicated across our universe, and my bathroom?

Assuming the multiverse theory is true, then each universe has a different set of constants and it provides a reasonable explanation as to why the constants in our universe seem set 'just right' for ...
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2answers
413 views

How can a cosmological constant be a candidate for dark energy if the universe is flat?

How can a cosmological constant be a candidate for dark energy if the universe is flat? Doesn't a cosmological constant in EFE give rise to positive/negative or no curvature to the universe? I mean, ...
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1answer
69 views

Lorentzian Einstein metric where $R_{ij} = g_{ij}$?

Does there exist a Lorentzian metric $g_{ij}$ (with signature $-,+,+,+$) which also satisfy that $g_{ij}=R_{ij}$ (e.g. is Einstein with $k=1$)?
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1answer
86 views

Generalising a finding in Kaluza-Klein theory to extra spatial dimensions in super string theory a correct method?

As a disclaimer I am an A-level student. I have been doing a research project in which I am looking at manipulating space-time through the ideas provided by superstring theories. I stumbled upon the ...
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0answers
194 views

Does anything exist outside of space?

I was doing a little poking around about just what is a massless particle and what that means when I came across this paragraph: If we hop in a spaceship that can go 90% the speed of light, we are ...
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3answers
1k views

Does empty space have energy?

My physics friend suggested that "the answer to why matter exists in the universe" is because all massive particles are just the fabric of space excited into little packets. To illustrate, imagine a ...
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1answer
112 views

Could Dark Energy be evidence that space equals energy, in a similar manner to $E=mc^2$?

I was reading another Phys.SE question and answer, and this quote jumped out at me: As for dark energy, the current accepted model, Λ-CDM, treats dark energy like a constant energy density. That ...
6
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1answer
135 views

What does the Friedmann Equation imply for the cosmological constant?

The Friedmann equation is given by $$(\frac{\dot{a}}{a})^2 = \frac{8 \pi G \rho}{3} - \frac{kc^2}{a^2} + \frac{\lambda c^2}{3}.$$ Considering that the left hand side is analagous to the kinetic energy ...
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1answer
121 views

Before Dark Energy was discovered

I'm really confused on this topic. Pardon my French if my questions seem really stupid. Before Dark Energy was discovered in 1998 did scientists know that the cosmological constant calculated, I ...
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1answer
294 views

Is cosmological constant really constant?

As the Universe expands, the dark energy in it also increases. I heard that the cosmological constant $\Lambda$ represents dark energy, so that constant must change as time passes, right? Correct me ...
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1answer
457 views

Why does the flatness problem (of the universe) present a fine tuning problem?

The Friedmann equation can be written $$|\Omega-1|=\frac{|k|}{a^2H^2}$$ In a period where the universe is decelerated $a^2H^2$ becomes bigger as we extrapolate into the past. We know $|\Omega-1|$ ...
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0answers
192 views

Why is Weinberg's prediction of omega sub lambda ($\Omega_{\Lambda}$) other than sophisiticated tautology?

I am not a physicist, but I do have a background in engineering (EE and computer science) and have followed physics and cosmology on a primarily conceptual basis for many years. I have looked at ...
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1answer
394 views

Should Anti de Sitter Universe collapse exponentially? (n0)

The de Sitter Universe is described by the Friedmann equation with $k=0$, $\rho=0$ and a positive cosmological constant $\Lambda$: $$\Big(\frac{\dot{a}}{a}\Big)^2=\frac{\Lambda c^2}{3}$$ The ...
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2answers
261 views

Why doesn't the cosmological constant cause black holes to form?

The cosmological constant acts as matter with positive energy but negative pressure. Then a region $R$ should have energy $E\sim \Lambda r^3$. On the other hand, we know that the energy for a black ...
6
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1answer
531 views

Entropy of the cosmological constant and the laws of thermodynamics?

Convention The convention being used is: $ A_{C} = $ The classical variable Premise Consider the following toy-model universe: A universe with a positive cosmological constant. Basic ...
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1answer
137 views

Thought experiments about $c$ [closed]

Poincare had a brilliant thought experiment about what if everything in the universe doubled in size, would anybody notice any difference or even be able to measure anything that can be compared with ...
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0answers
62 views

How come the cosmological constant supports the idea of dark energy existing? [duplicate]

According to an article I've read recently, the cosmological constant was used to support the theory of dark energy. But the cosmological constant already defines an inclination in the essence of ...
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2answers
7k views

Lorentz invariance of the Minkowski metric

As far as I understand, one requires that in order for the scalar product between two vectors to be invariant under Lorentz transformations $x^{\mu}\rightarrow x^{\mu^{'}}=\Lambda^{\mu^{'}}_{\,\,\...
5
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1answer
149 views

Doesn't the presence of dark energy make the flatness problem less important?

If the cosmological constant (aka dark energy / vacuum energy) were zero, then an Omega greater than 1 would mean both positive curvature and a recollapse while an Omega less than 1 would mean both ...
16
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1answer
682 views

The cosmological constant as a Lagrange multiplier?

The cosmological constant $\Lambda$ can be introduced into the gravitational action like this : \begin{equation} S = \frac{1}{2 \kappa} \int_{\Omega} (R - 2 \Lambda) \sqrt{-g} \; d^4 x + \text{matter ...
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3answers
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G4v Gravity Theory: Why does this get rid of Dark Energy?

Earlier this year, Carver Mead of CalTech published a paper which seems to be garnering a lot of attention: http://arxiv.org/abs/1503.04866 http://www.npl.washington.edu/AV/altvw180.html http://...
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1answer
1k views

Is there a relationship between the Cosmological constant and the Hubble constant?

I looked around to see if this precise question was asked before and it appears not to be. So is it just me or has anyone else noticed that, no matter what consistent set of units you use, $$ \...
5
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2answers
131 views

What evidence is there for additional dark energy coming into existence when space increases?

As I understand since cosmological constant is a 'constant' - increasing the space must generate additional dark energy that fills that space This does sound counter-intuitive to me, but I am sure ...
4
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1answer
106 views

What is the analogous effect of cosmological redshift for particles with mass?

Due to the metric expansion of space, light emitted from earlier times in faraway parts of the universe and travels for a long time to reach us get progressively redshifted, decreasing the energy of ...
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0answers
50 views

Problems of General Relativity on small and large scales [duplicate]

As far as I know, the most important problem of GR on large scales is the cosmological constant problem which in some manner can be thought of as a dark energy problem (please correct me if I am wrong)...
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0answers
26 views

Cosmological constant in General Relativity [duplicate]

According to my GR notes the cosmological constant can be thought of as a vacuum energy much in the same way as the ground state of the harmonic oscillator. The notes claim that the regularised energy ...
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1answer
153 views

Is it possible to directly test whether of not the vacuum gravitates?

According to GR, all sources of stress-energy (e.g. everything on the $T_{\mu\nu}$ side of the EFE) should gravitate (e.g. affect the curvature/$G_{\mu\nu}$ side of the EFE). We observe the expansion ...
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1answer
363 views

Difference between Cosmologial Constant and Quantum Vacuum State

Hello I am very new to cosmology and quantum physics. I need some basic understanding (in Layman's term) of the Difference between Cosmological Constant and Quantum Vacuum. Cosmological Constant is, ...
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3answers
262 views

Does general relativity entail singularities if there's a positive cosmological constant?

I've heard that Hawking and Penrose proved that general relativity entails singularities. But it says in the abstract of what seems to be the paper in which they proved it (The Singularities of ...
4
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0answers
192 views

Locality, unitarity & vacuum energy

I've read in a set of lecture notes that the requirement of locality and unitarity in QFT imply that the vacuum must have a non-zero energy associated with it (http://arxiv.org/abs/1502.05296 , top of ...
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0answers
394 views

The fate of Poincaré recurrence with the Big Rip

Recently, there has been a lot of talk in the media about the "Big Rip". It most certainly resulted from the paper by Marcelo M. Disconzi and Thomas W. Kephart where they have figured out a ...
2
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2answers
171 views

Cosmological constants

I've heard that the cosmological constant is 0.[123 more zeros] and then a 1 [in some units]. Does that means that it used to be exactly zero? Is the value of this constant changing or is it fixed at ...
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0answers
287 views

How to find de Sitter and almost de Sitter solutions in (super)string theory

From Cosmology, we have learned that we live in an almost de Sitter (positively accelerated!) Universe. It seems that dS space solutions in superstring/theory are problematic and there are some no-go ...
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1answer
333 views

Cosmological Constant on the LHS of Einstein's Field Equation

The cosmological constant seems to be normally described as an energy (repulsive force, Dark Energy) of Space-Time. I was just wondering, if we were to interpret the cosmological constant as being ...
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0answers
163 views

What are the zero point energy densities of the individual quantum fields?

I'm reading through "General Relativity - An Introduction for Physicists", by Hobson, Efstathiou, and Lasenby, and I have a question regarding one of the statements related to the cosmological ...
2
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1answer
186 views

Generalized Bekenstein-Hawking temperature for Kerr-Newmann-dS black holes

What is the formula for the Bekenstein-Hawking temperature in a Kerr-Newmann-de Sitter spacetime, i.e., the temperature for a black hole with Mass (M), angular momentum (J), electric charge (Q) and ...
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1answer
166 views

Connection between the cosmological constant $\Lambda$ and the cutoff scale $\Lambda$

I'm trying to understand the connection between the $\Lambda$ from cosmology and the $\Lambda$ from QFT. Cosmology: The cosmological constant enters the Einstein equations. In the special case of the ...
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0answers
62 views

Cosmological constant theories

Are there any hypotheses on the expansion of the universe, which have a cosmological constant, or some other parameter, that results in a universe with an ever increasing rate of acceleration for the ...
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5answers
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Negative pressure, tension, and energy conditions

We have lots of common everyday experience with positive pressure, the canonical example is a gas. But other examples of positive pressure are easy to imagine: for instance, a solid that gets ...
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1answer
260 views

How can we know that virtual particles exist everywhere in space and not just locally around individual particles our are universe as a whole?

The metaphor of virtual particles that inhabit all of space is used to explain quantum fluctuations. This ceases to be just a metaphor due to the effects of gravity as clumps of any energy (not just ...
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1answer
126 views

Is there any paper analyzing the validity of Relativity in expanding space? [duplicate]

Big Bang models result from applying Relativity equations to expanding space; however, as Einstein noted, Relativity was not established in expanding space. A basic question arises: is Relativity ...
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1answer
79 views

Why do scientists use a different method from redshift to find the distance of distant galaxies?

The method I am referring to is measuring the brightness of a super nova. Does the redshift method even work at that distance and if it doesn't why not? If it does work why do they prefer to use the ...
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2answers
371 views

Would cosmological redshift be present in the following situation?

I'm trying to understand if cosmological redshift is just a secondary form of doppler redshift, or something else entirely. Suppose the two galaxies in the picture are receding from each other, but ...
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3answers
2k views

Expanding universe as predicted by the Einstein Field Equation

Without the cosmological constant, the Einstein field equation predicts the universe is expanding. Why is that? It is counter-intuitive because generally gravity should pull things closer and shrink ...
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2answers
340 views

Why is the cosmological constant a scalar?

Maybe my understanding is just off, but the cosmological constant is just a scalar, right? What are it's units? Why a scalar? - was a tensor 'cosmological constant' ever considered or is it just not ...
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1answer
237 views

Why is it so hard to find out the sign of the cosmological constant?

Correct me if I am wrong (it is in fact part of my question :) ) but from the little I know about the cosmological constant, growing existing evidence is still insufficient to tell whether $\Lambda$ ...
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2answers
2k views

Does spacetime have a “mass” value? or What is “Spacetime” made out of?

When measuring the MASS within the Universe, does "space" or "spacetime" have a value? I only ask, because when speaking of expansion, space is expanding. Could it be possible, to reverse the process,...
3
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1answer
97 views

Effect of cosmological constant on time

The cosmological constant is introduced in Einstein equations in the form : $G_{\mu\nu} = T_{\mu\nu} + \Lambda g_{\mu\nu}$, as I understand it, shouldn't the term $\Lambda g_{\mu\nu}$ have effects on ...