The universe (Latin: universus) is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. According to estimation of this theory, space and time emerged together 13.799±0.021 billion years ago, and the universe has been expanding ever since. While the spatial size of the entire universe is unknown, the cosmic inflation equation indicates that it must have a minimum diameter of 23 trillion light years, and it is possible to measure the size of the observable universe, which is approximately 93 billion light-years in diameter at the present day.
The earliest cosmological models of the universe were developed by ancient Greek and Indian philosophers and were geocentric, placing Earth at the center. Over the centuries, more precise astronomical observations led Nicolaus Copernicus to develop the heliocentric model with the Sun at the center of the Solar System. In developing the law of universal gravitation, Isaac Newton built upon Copernicus's work as well as Johannes Kepler's laws of planetary motion and observations by Tycho Brahe.
Further observational improvements led to the realization that the Sun is one of hundreds of billions of stars in the Milky Way, which is one of a few hundred billion galaxies in the universe. Many of the stars in galaxy have planets. At the largest scale, galaxies are distributed uniformly and the same in all directions, meaning that the universe has neither an edge nor a center. At smaller scales, galaxies are distributed in clusters and superclusters which form immense filaments and voids in space, creating a vast foam-like structure. Discoveries in the early 20th century have suggested that the universe had a beginning and that space has been expanding since then at an increasing rate.According to the Big Bang theory, the energy and matter initially present have become less dense as the universe expanded. After an initial accelerated expansion called the inflationary epoch at around 10−32 seconds, and the separation of the four known fundamental forces, the universe gradually cooled and continued to expand, allowing the first subatomic particles and simple atoms to form. Dark matter gradually gathered, forming a foam-like structure of filaments and voids under the influence of gravity. Giant clouds of hydrogen and helium were gradually drawn to the places where dark matter was most dense, forming the first galaxies, stars, and everything else seen today.
From studying the movement of galaxies, it has been discovered that the universe contains much more matter than is accounted for by visible objects; stars, galaxies, nebulas and interstellar gas. This unseen matter is known as dark matter (dark means that there is a wide range of strong indirect evidence that it exists, but we have not yet detected it directly). The ΛCDM model is the most widely accepted model of the universe. It suggests that about 69.2%±1.2% [2015] of the mass and energy in the universe is a cosmological constant (or, in extensions to ΛCDM, other forms of dark energy, such as a scalar field) which is responsible for the current expansion of space, and about 25.8%±1.1% [2015] is dark matter. Ordinary ('baryonic') matter is therefore only 4.84%±0.1% [2015] of the physical universe. Stars, planets, and visible gas clouds only form about 6% of the ordinary matter.There are many competing hypotheses about the ultimate fate of the universe and about what, if anything, preceded the Big Bang, while other physicists and philosophers refuse to speculate, doubting that information about prior states will ever be accessible. Some physicists have suggested various multiverse hypotheses, in which our universe might be one among many universes that likewise exist.
I know of some physicists (e.g Holger B Nielsen, Grigory Volovik or Edward Witten) who have proposed that all symmetries (Local gauge symmetries associated with forces and dynamics and global symmetries associated with conservation laws) are emergent rather than fundamental.
Are there any other...
Hello! I was reading up on methods for determining the density of the universe and I came across this page: https://hypertextbook.com/facts/2000/ChristinaCheng.shtml
I tried using equation stated, Ω=(2/3Λ)(c^2/H^2), with SI unit versions of both variables:
Λ=1.1056 * 10^-52 m^-2
H=2.1927 *...
In the universe do straight lines exist? I know over long distances like interstellar and even shorter distances like between the Earth and around the gravity of the moon lines tend to curve, but do straight lines exist anywhere? Or just a desire for them to exist in nature if not for gravity...
https://www.space.com/4271-huge-hole-universe.html
I would much appreciate any links cited to more information about this hole, especially more recent information. I would also appreciate any information to clarify the following questions.
How much baryonic matter is actually present (taking...
UNITS
m is meters
kg is kiliograms
K is degrees Kelvin
s is seconds
J is joules
u is daltons = 1.66053906660(50)×10−27 kg
https://en.wikipedia.org/wiki/Dalton_(unit)
1 pc = 3.085678 x 1016 m
CONSTANTS
MH = mass of hydrogen atom = 1.007825 u
= 1.673532784796145 ×10−27 kg...
Would it be correct to say, that gravitational waves of the magnitude that is currently detected by LIGO and similar detectors, are prevalent to the extent that there is no single location in the known universe, that such magnitude of gravitational waves, don't pass through at least several...
It's straightforward to calculate the wavelength of the balls which is 20,000m. I said that because this is the case and then the pattern must not be a an interference pattern as with electrons.
The second question relies on the formula d = n(lambda)/2. Setting n = 1 for two golf balls will...
Hello everyone! I was listening to a podcast that featured a cosmologist and she mentioned that if the universe was positively curved (and therefore a sphere overall), light would travel around the universe and then end up where it started. I wondered, would a gravitational wave do the same?
I am certain that my confusion here rests in a misunderstanding on my part and not in a mistake having been made by countless physical theorists. Nevertheless, I have had a hard time wrapping my head around it. Here is the crux:
We observe that light from distant objects is more redshifted...
I've come across the question of continuity vs discreteness in different articles, discussions, etc. but I'm not sure that I am 100% clear on what the precise question is.
My basic interpretation of it is a question of whether the Universe is made up of lots of separate entities which all...
I've read that before the big bang all the matter in the universe was contained within an impossibly small space. How can you have matter in a smaller space than if all the space was squeezed out of an atom (or probability cloud if you want to be pedantic). Also, how does it fit it with Pauli's...
I’m sure the resolution is something to the effect of “we can only apply special relativity in flat spacetime” but I’m hoping someone can explain in more detail.
Disclaimer: I don’t know general relativity.
So in a positively curved universe, if you keep traveling (let us neglect expansion)...
I was watching a video where Lawrence Krauss describes the big bang in terms of the observable universe. He says regions outside the observable universe need not have come from the big bang.
Starts At minute 3.
Hubbles law states the rate of recession of galaxies increases proportionally with distance, and the cosmological horizon is where distant galaxies recede away at the speed of light. Does this not violate the rule of faster than light speed travel?
In the book, it states that a universe is isotropic if it looks the same regardless of which direction you look at large enough scales. This seems fairly easy to prove these days with observations from galaxy surveys and the CMB. However, how can we possibly prove that the university is...
The Twin Paradox implies that the universe as a whole is a special frame of motion according to "Relativity Simply Explained" by Martin Gardner. I want to be sure than I haven't misunderstood something. I don't find the explanation completely clear. If the universe as a whole is a special and...
I came upon a realization recently.
The early universe is always described to have begun in a state of extremely low entropy and it's been increasing ever since.
But the same amount of stuff exists now as it did back then. Only thing that's changed is how big the universe is now vs then.
So...
In the known universe, the number of electrons seems to be greater than that of positrons since electrons are within every atom around us. However, when a gamma ray approaches a nucleus, a pair consisting of an electron and a positron, can be created from pure energy. If all matters are created...
Although we don't have any other Universes to compare ours against, we generally accept that there is a large amount of matter in the Universe.
At the point of the Big Bang, what determined how much matter the Universe would contain? Would it have been equally probable, for example, for the...
I've been searching for weeks and still with the doubt.
I just know scientist look the content of the CMB and with general relativity calculates the expansion rate today that is 73 km/s/Mpc, but nowhere does it say how exactly. What does the contents of the universe have to do with the...
Suppose the universe were described by internal geometry by a ball, i.e. the metric where :
$$diag(1,r^2,r^2 sin(\theta)^2)$$
Now if we go to exterior geometry and suppose there existed a 4th timelike dimension the manifold were for example modelized by :
$$\left(\begin{array}{c}...
The perimeter of a circle increases by radius, the surface area of a ball increase by radius(which is height which is the third dimension if the ball is a planet like the Earth), and the universe is expanding by time, can we say that the fourth dimension is time by this ?
Could something older than our universe originating from another universe get sucked into a wormhole and wind up in our universe therefore being older than our universe itself?
As you all know:
Planck evidence for a closed Universe and a possible crisis for cosmology
https://www.nature.com/articles/s41550-019-0906-9
If confirmed, it would bring back the Big Bounce as a possible hypothesis for the evolution of the universe. This has long-term consequences being that...
I'm currently writing a research paper about the speed of light. I have researched universe expansion, specifically, the quantised redshift spectral index fluctuations of distant galaxies and other structures over time, however, I need to suggest why universe expansion possibly causes a recorded...
Sure it seems like an impossible feat but I need to gain a bit more depth, every little helps. I've been trying to analyse different things in life. Behaviours of other individuals', my own behaviour, our interaction with other conscious individuals, e.t.c. Essentially I've just been trying to...
According to the Many Minds interpretation of quantum mechanics (https://en.wikipedia.org/wiki/Many-minds_interpretation), the distinction between worlds in the Many Worlds interpretation should be made at the level of the mind of an individual observer. I have read that, in this case, each...
As inflation happens, effectively, faster than the speed of light (between any given two points) and we can only see 14 billion years back, is it possible the data we need, to judge the age of the universe, is actually beyond our detection abilities. Could the age of the universe be greater...
What percentage of the universe’s A) total mass —including dark matter— and B) radiation energy is estimated to reside in:
Inter-galactic space covering i) inter-galactic medium and ii) distinct inter-galactic astronomical objects; and
Galaxies covering iii) inter-stellar gas clouds, iv) stars...
https://www.google.com/amp/s/phys.org/news/2019-11-universe-rethink-cosmos.ampWhat do the results of the closed universe study tell us in terms of past cosmic sequences, if it is indeed the proper description of the universe?
Would it entail a self-contained universe? By self-contained I mean...
In https://en.wikipedia.org/wiki/Zero-energy_universe and in https://en.wikipedia.org/wiki/Negative_energy, the idea of a negative energy balancing out the positive energy in the universe is advanced. However, these two sites use descriptions of "quantum fluctuations", "virtual particles"...
Does the expansion of the universe affect orbits? Would the orbits of the Magellanic Clouds, for example, be different if the universe were not expanding? If orbits are affected, at what scale do we first detect the effects?
Usually questions I have of this nature are down to my limited understanding of the concepts, and this may be no different. Based on my understanding of the Block Universe interpretation of relativity, it appears to me as though there is a conflict between Bell tests and the Block Universe.
To...
Just a heads up, this post is quite long. I've tried to be as detailed as possible from the outset because I find it can help avoid the need to clarify things later, or helps when clarifying things later. There is only one question posed at the end, but I think it might be useful to read the...
Summary:: What percent of the universe is outside of galaxies?
Hello,
What percent of the universe is outside of galaxies?
I need this information for a writing piece I am doing. I need specifically to be able to state that if someone was to randomly relocate to somewhere else in the...
The expansion of the universe is accelerating. So the big rip is the best bet for how it ends isn't it? This fellow seems to think so:
I guess the heat death is not the most likely, unless new evidence shows otherwise.
In this book series George, a school kid meets a neighbor Eric, a scientist . He's surprised to find that Eric possesses a supercomputer which can actually actually teleport people to space.
The book explains astronomical concepts like the red shift, true vacuum and false vacuum for instance...
I read somewhere that expanding universes create more energy as they expand, and I was thinking over time there would be a considerable amount of energy created due to this expansion. Even with a very small cosmological constant the energies created over time would probably dwarf anything that...
I have a question about the history of cosmology, hope its okay to ask here. Who was the first person since Einstein's Gr to point out a singularity in cosmology? I know Freidman talked of an expanding universe and Lematire a primeval atom. But were there any explicit mentions of the density of...
Summary:: I would like clarification about universe expansion.
Hello
I would first like to see if my entry level understanding of how the expansion of the universe is obtained or measured. (In a very basic model or example)
First:
My current understanding is that one way the distance to...
When we say the universe is "flat," do we mean:
1) If you could hypothetically "zoom" out to the edge of the universe it would appear roughly as a flat like a sheet of paper with local fluctuations / bumps to indicate the presence of matter.
2) If we draw 2 parallel lines from 1 location they...
I was discussing a problem related to Einstein's universe model. As we all know its an unstable equilibrium. So a small fluctuation in the density would result in an either expanding or contracting universe. However, I read that
"There are static and stable solutions in Newtonian gravity...
The expansion of space is about 68 km/s/Mpc, or 0.00002 km/s/light year. The radius of the sun is about 700000 km. Thus, initially ignoring additional forces, the change in radius of the sun due to the expansion of space is about 1.5*10^-9 m/sec, or 5 cm/year.
I assume that this expansion is...
I’ve read many Legends and Canon Star Wars books and I always take away stuff on their limits of technology and science. Over the years; here are some things they said science can’t do.
1.) Cybernetic liver- In Lost Stars, it was said Ciena’s liver could not be replaced as it was one of the...
I am trying to derive the equation for a case, where we have a dust(zero-pressure) in an expanding universe.
There are 4 equations but I think exercising on one of them would be helpful for me.
I am trying to derive the equation for a case, where we have a dust(zero-pressure) in an expanding...
I'm quoting from Wikipedia the article about GN-z11 (the oldest and most distant known galaxy):
"At first glance, the distance of 32 billion light-years (9.8 billion parsecs) might seem impossibly far away in a Universe that is only 13.8 billion (short scale) years old, where a light-year is the...