All Questions
Tagged with cosmology experimental-physics
62
questions
2
votes
1
answer
137
views
Which evidences do we have that general relativity works at large scales?
Recently I've been reading Pedro Ferreira's SciComm book The Perfect Theory: A Century of Geniuses and the Battle over General Relativity. At one of the last chapters, which discusses modified ...
- 22.1k
1
vote
1
answer
85
views
Tests for general relativity
As a theorist, I’d guess that in Newtonian gravity we can check for proportionality to mass, and inverse square proportionality to distance, by measuring the ratios of gravitational forces.
Is there ...
0
votes
0
answers
23
views
How would red (frequency) shift work for sound waves on the surface of a balloon?
Imagine an expanding balloon with a source of vibrations, in the fabric of the balloon, on one side (pole), and a microphone on the other side (pole). We would expect the sound to be 'red shifted' ...
- 371
2
votes
1
answer
98
views
What do WMAP CMB Temperature map values represent exactly?
I understand that Cosmic Microwave Background Radiation Map provided by WMAP survey in HEALPix pixelization format is nothing but an array of temperatures associated with the cmb radiation coming from ...
2
votes
1
answer
146
views
Problem with the Fisher information matrix in case of $N$ measurements of two observables
Let consider two observables, $x$ and $y$. Suppose that $y$ depends on the independent variable $x$ through the model $m(x; \boldsymbol{\theta})$, where $\boldsymbol{\theta}$ is a vector of model ...
- 43
1
vote
1
answer
103
views
By what experiment is the vacuum energy density actually measured?
I have heard that the actual vacuum energy density which is up to 120 orders smaller than the predicted QED value can be measured in experiments or cosmological observations?
What are these ...
- 4,170
1
vote
1
answer
132
views
How to rule out that the speed of light was different in the past?
The constancy of the speed of light is a fundamental principle in modern physics, and it is supported by a wide range of current experimental evidence.
There is no evidence to suggest that the speed ...
- 489
0
votes
2
answers
137
views
*Observational* Consequences of Energy Nonconservation in GR
What are the experimental or rather observable consequences of the non-conservation (or conservation) of energy in GR? Imagine our instruments were $10^3$ or even $10^6$ more sensitive, better ...
- 19.7k
0
votes
0
answers
45
views
Spacetime of a quantum measurement
In a classical(or wave) picture, when we measure a doppler effect from a receding galaxy, we are working on two wave crests essentially. Therefore, there are two events in spacetime for such detection....
- 2,794
1
vote
0
answers
96
views
Experimental Test for the cyclic $G_{earth}$ prediction of a Cosmological Model
Can anyone suggest a way to measure or rule out a tiny cyclic variation in the earth’s gravitational constant $G_{earth}$, predicted by an alternative cosmological model? It’s an annual cyclic ...
- 13.7k
1
vote
2
answers
383
views
Frequency sensitivity of gravitational wave interferometer with its armlength and with mass of the mergers
To the best of my knowledge, LIGO is capable of observing gravitational waves (GW) from stellar mass black hole (BH) mergers but not mergers of supermassive black holes. In order to detect the latter ...
- 26.8k
0
votes
1
answer
63
views
How do we obtain matter-lambda curve?
I have 400 supernovas type Ia's distance modulus and its error and redshift.
how can I obtain an elliptic curve like the one in image for my datas?
where did that elliptic came from?
- 75
2
votes
2
answers
85
views
Research in next decade on dark matter: sky surveys vs particle detectors
The next decade is very promising for cosmology as new surveys such as SPHEREx, Roman, Euclid, DESI which will shed light on inflation, dark matter/energy and more. At the same time there are particle ...
- 4,576
1
vote
2
answers
76
views
What difference does the wavelength and/or frequency of a gravitational wave make? On the detector, for instance?
When they talk about the arms of LIGO or Virgo stretching by a thousandth of the width of a proton, they always emphasize that this is the wave's amplitude, not wavelength...
The wavelengths are ...
- 4,509
0
votes
1
answer
54
views
Observational evidences of the early universe other than CMB
CMB is a great experimental evidence that the universe was once in an hot themal phase at early times. Supposing all the CMB observations failed for tecnical reason (for example the rocket shipping ...
- 505
1
vote
0
answers
52
views
What are the key pieces of cosmological evidence if you want to compare the success of dark matter versus quantised inertia?
Quantised Inertia is a controversial fringe theory that is claimed to be an alternative explanation of, for example, galactic motion.
The consensus explanation for why the outer stars in galaxies ...
- 2,572
-2
votes
2
answers
153
views
Is Young Earth universe distinguishable from non-creationist one? [closed]
While talking today about some religious beliefs I was struck by the next question:
So what if some super-natural being forks our universe 6,000 years
ago, i.e. creates the exact same copy of ...
- 141
1
vote
0
answers
52
views
Tianqin project vs LISA
How does Tianqin space-based gravitational wave detector compare to LISA? Will it be able to detect gravitational waves from e.g. inflation (considering possible upgrades)?
- 2,726
0
votes
1
answer
210
views
Estimate of neutrino masses from the values of $\Delta m_{21}^2$ and $\Delta m_{13}^2$ only!
The blog here says that
The measured mass differences between the eigenstates are $\Delta m_{21}^2=7.5\times 10^{-5} {\rm eV}^2$ and $\Delta m_{13}^2=2.5\times 10^{-3} {\rm eV}^2$, suggesting that ...
- 26.8k
1
vote
4
answers
885
views
Does the unobservable universe exist in the present?
Is our observation about universe limited due to the incapacity of telescopes to look further or is it just because we look too further into the future, so the "unobservable" universe hasn't been ...
- 113
41
votes
5
answers
13k
views
Is light actually faster than what our present measurements tell us?
It is well established that the light speed in a perfect vacuum is roughly $3\times 10^8 \:\rm m/s$. But it is also known that outer space is not a perfect vacuum, but a hard vacuum. So, is the speed ...
user182521
1
vote
1
answer
212
views
Precision in cosmological constant
The observed cosmological constant, what is its precision? How precise do we know is it not a fluke or misinterpretation of cosmological data?
- 6,611
0
votes
1
answer
253
views
Are physicists still ignorant of the existence of real singularities?
(1) Is the gravitational singularity (or space-time singularity) the same as the black hole singularity?
(2) The wikipedia page says
Physicists are undecided whether the prediction of ...
- 61
2
votes
1
answer
133
views
How is the primordial abundance of Lithium measured?
I was reading about the "Lithium problem" and I came across this Physics SE post: Discrepancy problem in lithium?
The answer mentioned
On the other hand, measurements of the $\rm Li$ abundance ...
user191954
6
votes
0
answers
66
views
Sterile (4th) neutrino and cosmological bound
Recent results by MicroBoone seems to give support to old LSND experiment in favor of a fourth neutrino (sterile). How does it fit with the current cosmological bound for neutrinos?
- 6,611
1
vote
0
answers
45
views
Experimental constraints on dark matter pressure?
The $\Lambda$CDM model assumes collisionless dark matter, so that its pressure $P=0$. But what are the best experimental constraints on $P$? I guess on $P/\rho$ in fact…
user175150
1
vote
1
answer
125
views
Is quantum theory useful to describe the whole cosmos? [closed]
We often say that QFT describes the nature on a fundamental level. However this is indeed a very complicated theory for which the calculations related to the interaction of just a few particles simply ...
user56963
1
vote
0
answers
125
views
Fisher Forecasting For EUCLID Experiment Help [closed]
I'm trying to recreate the results of this paper https://arxiv.org/abs/1607.08016
to obtain the constraints for the matter density and hubble constant h.
However every time I try to create there ...
- 179
1
vote
0
answers
137
views
Experimental test for a universal scale closed timelike curve?
So recently, in chat, I was interested in about what if our universe contains only one CTC (thus making it unlike the Gödel metric, van Stockum dust where there can be more than one CTCs found) and ...
- 935
1
vote
1
answer
591
views
To what accuracy do we know the value of the cosmological constant?
The Wikipedia article just says that the cosmological constant
"is measured to be on the order of $10^{−52} \text{ m}^{−2}$," but the only citation goes all the way back to 2004. What is $\Lambda$'s ...
- 48.4k
5
votes
1
answer
152
views
What are some experimental verification of the non-linearity of gravitation?
According to my (limited) knowledge, all experiments to date probe only situations which can be understood using the linearized version of general relativity. For example, measuring gravitational ...
- 2,568
16
votes
2
answers
3k
views
What evidence do we have that CMB is the result of the Big bang?
I got the main picture repeated over and over again about why if there's a Big bang we indeed should see the CMB with this feature. In this question I'm asking something different: what independent ...
- 944
3
votes
1
answer
77
views
Running Constant Values At Very Low Temperatures
From Wikipedia Coupling Constants, using QED as an example. I realise that the one-loop beta function in quantum chromodynamics is negative.
If a beta function is positive, the corresponding ...
user108787
2
votes
0
answers
59
views
Any method to determine the gravitational constant $G$ from observations in cosmological scale?
By the observations in cosmological scale, I mean observations by astrophysicists like motions of quasars in far distance from us, relative motions of our galaxy to others, etc.
I know the famous ...
- 189
3
votes
1
answer
133
views
How was hydrogen gas (H) obtained by spectroscopists? Why is there more H than H2 in space?
Introductory quantum mechanics lessons talk about emission and absorption spectra for the hydrogen gas, and then give you an explanation as if this gas were pure $H$ atoms, and not the $H_2$ molecule (...
- 1,619
3
votes
1
answer
1k
views
Is there any evidence against the Cosmological Principle?
I have been slowly getting more into math, but haven't gone into differential geometry or anything like that yet, so this question might be basic. Trying to get a deeper understanding of the ...
- 2,200
3
votes
1
answer
147
views
The actual space curvature
What is the curvature of our physical space, according to the latest experimental data? I've found it somewhat difficult to find a definitive answer to the question, because the spacetime curvature ...
- 33
2
votes
1
answer
236
views
How do we get the power spectrum through the CMB?
How do we get the power spectrum through observing the CMB?
- 11
3
votes
5
answers
4k
views
Where does General Relativity (GR) fail experimentally? Experimental shortcomings of GR?
When speaking with researchers and professors at my physics department, I sometime catch this undertone in the conversation when speaking about GR: almost as if some are not entirely convinced about ...
- 3,719
11
votes
1
answer
700
views
The status of the BICEP2 'discovery' after Planck 2014
The tumultous period after the original announcement that the BICEP2 experiment had supposedly detected strong evidence of cosmological inflation in the form of B-mode polarization in the cosmic ...
- 16.4k
16
votes
3
answers
1k
views
What is the most compelling evidence of General Relativity in the presence of matter and energy?
The most oft-cited triumphs of GR are things such as the shifting perihelion of Mercury, gravitational redshift experiments, and gravitational lensing. But, as far as I know, these are only ...
- 2,046
1
vote
1
answer
82
views
Data/signal from a black hole to observe a singularity
I wonder if a situation is possible where, we measure some signal/property concerning a black hole. Supposing the measurement we make with some telescope, gets us the Fourier transform coefficients of ...
- 2,152
2
votes
2
answers
177
views
How do we observe the expansion of the universe?
This is my first question.
So I was reading about expansion of the universe and from what I've seen, the only way that we know that universe is expanding is by measuring redshift.
Also, here it says ...
- 31
2
votes
4
answers
339
views
What experiment would disprove Friedmann model of cosmology?
What experiment would disprove Friedmann model of cosmology?
As a layman, I have read a lot of articles and threads in specialized forums. I am probably wrong, but I developed an impression that that ...
- 5,854
7
votes
2
answers
659
views
What experiments compete with BICEP 2, and when are their results expected?
The recent results of the BICEP 2 experiment published on March 17th 2014, has generated a lot of media attention, with the general consensus being that "this is a major discovery" perhaps leading to ...
- 3,108
81
votes
6
answers
7k
views
What was the major discovery on gravitational waves made March 17th, 2014, in the BICEP2 experiment?
The Harvard-Smithsonian Centre for Astrophysics held a press conference today to announce a major discovery relating to gravitational waves. What was their announcement, and what are the implications?
...
- 5,569
1
vote
1
answer
120
views
Multiverse explanation of fine tuning of cosmic constants
Physicists proposed the idea of multiverses to explain extraordinary fine tuning of the cosmic constant and physical laws which is essential for rise of life on earth.
Is there any experiment that ...
9
votes
1
answer
1k
views
What are the different ways to measure the spatial curvature of the universe?
Just what the question asks. Assuming the Friedmann-Rovertson-Walker (FRW) metric, what measurements can be performed to determine the spatial curvature of the universe.
- 3,492
17
votes
9
answers
17k
views
What is the difference between translation and rotation?
What is the difference between translation and rotation ?
If this were a mathematics site, the question would be at best naive.
But this is physics site, and the question must be interpreted as a
...
- 3,798
2
votes
1
answer
3k
views
Is the total angular momentum of the universe zero? [duplicate]
I know that having a net angular momentum will contradict isotropy of the universe by preferring a specific direction. But is there any experimental data on the total angular momentum of the universe ...
- 6,004