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.
By fitting redshift distance data we can estimate the present Hubble rate H0 and the longterm limit that the Hubble rate is tending towards H∞.
The Age (how long the universe has been expanding) can be calculated just from those two measurements, assuming the spatial-flat standard cosmic...
I want to know Universe density according to this equation( ##k=-1##) ?
##H^2(t)-8πρG/3=-k/a^2(t)##
##ρ_U=ρ_m+p_r##
##ρ_U##=Universe density
##ρ_m##=Matter density
##p_r##=Radiation density
Homework Statement
The evaporation enthalpy of Hg is ##59.3 kJmol^-1## at its boiling temperature ##356.6ºC##. Calculate:
(a) the vaporization entropy of Hg at this temperature
(b) the change in entropy of the surroundings and universe
(c) the vaporization entropy of Hg at 400ºC.I was also...
I still don't understand this fully. Can someone please explain? I saw a video where an analogy was made, the distant observer is like an accelerating observer in flat spacetime and guy falling in is like an inertial observer, is it just like the coordinates of the distant observer from the...
Hi people. I just read some articles about physicist starting to gain more and more evidence for the Universe to be a 3D Hologram of a 2D world (or that's how I understood it). And apparently for us living in a "Matrix", like the one in the movie. Now I would like to understand the relation...
Dear PF Forum,
Sorry to ask this question again after so many threads here and in google that explain nothing!
And many controversies, too.
1. Does the universe really comes from nothing? Yes or No?
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2. if "YES" then...
What...
Dear PF Forum,
Again the same question about preferred frame of reference. I have read several threads in Physics forum, but I think this question belong to cosmology. And I have searched in Google and in PF forum threads, so, I'll ask some confirmation here.
1. Does the universe have a...
Viewpoint 1:
Because gravity or other forces that are holding the thing concerned (be it a galaxy, a ruler or an atom) together are way stronger than the "force" caused by the expansion of space. So strictly speaking, space does in fact expand everywhere, including the space inside an atom...
I found this article interesting it does away with dark energy and dark matter. two of the things i hate in cosmology.
On the nature of cosmological time
Pierre Magain, Clémentine Hauret
Comments: 5 pages, 4 figures, submitted to MNRAS
Subjects: Cosmology and Nongalactic Astrophysics...
Alan Guth mentioned in his lectures that to get the accurate linear relationship of Hubble's law, we need to subtract the velocity of the Earth with respect to the cosmic microwave background (CMB) when calculating the velocity of galaxies.
Question 1:
If space is expanding uniformly...
Hi i have a question, i m a engineer but i have probably a dumb question ¿if the Expansion of the Universe is accelerating, but exist a speed limit "c" this tell me that at one point the universe will expand at a constant rate?
Hello everyone,
As you can see, I am new on this forum. In my first thread, I decided to ask one very interesting question, maybe one of the most shocking questions which exist at this moment.
We all know the data which have been provided of WMAP and Planck satellites, and what this data shows...
What If we accept starting point of the big bang as the central point and what If the equatorial expansion rate of a spinning universe was the speed of light, how would it impact universe?
( In this question, you may think yourself as an observer from out of universe. I try to mean with "the...
When temperature of the universe falls below nucleon mass ##T<<1## GeV, the number densities of nucleons (proton and neutron) which are in kinetic equilibrium can be obtained as
##n_i=g_i (\frac{m_i T}{2\pi})^{3/2} e^{\frac{\mu_i-m_i}{T}}##. Since baryon number should be conserved, then I...
My understanding:
When we draw a triangle on a flat piece of paper and measure the angles using a protractor, the sum of the angles is ##180^\circ##. So we conclude that the universe is locally flat. Suppose we draw a very big triangle that spans across galaxies (say, using lasers and mirrors)...
Kolb&Turner in "the early universe" mentioned that for a scalar field ##\phi## at finite temperature, ##p=-V_T(\phi)## and ##\rho=-p+T\frac{d p(T)}{d T}## where ##V_T## is potential energy including temperature correction. My question is: when we consider the evolution of the universe using...
Would someone like to have a conversation with me about the bounds of the universe and energy? I have a few ideas rambling around.. When I say bounds I mean the expanding bubble. But I would like to discuss infinite matter and infinite energy big crunch possibility. I'm a beginner with BIG thoughts.
Dear PF forum,
I once read that the universe IS nothing. And "FROM", too.
But I like to ask about "IS".
They say that "Gravity" is negative energy. So if you add all the masses and energies and gravity, it would be zero.
What I'd like to ask is this.
A. Is all Mass + Energy + Gravity = 0?
B. Is...
Dear PF Forum,
After searching many links in Google and threads in PF, I can't find the farthest object in the universe. I have some questions here, perhaps someone can give me quick and simple answer.
A. What is the farthest object in the universe? How far away?
B. The radius of the...
If you take the size of the observable universe can you find out how many cubic plank lengths can fit in the observable universe and it doesn't have to be exact just approximation.Also the math and formulas would be helpful too.
Whenever I attempt to research this question, my search results yield "Is the Universe Infinite" where the question ALWAYS refers to the volume of the universe. This question is usually answered along the lines of: "If the universe is closed, than it's volume, aka it's 3D surface area in...
There is a series of very interesting science fiction films lately related to physics and from Marvel Universe. To those dizzy already or want to relax from Many Worlds or unsolved problems in physics, etc. Try to watch the latest Avengers: Age of Ultron. I have to watch it the second time to...
I know that universe can be have three different futures.But for lastes theories universe is growing faster then we thought.I want to ask how much energy we need to make this observable universe.
What are the lines of investigation right now? I'd have listened that it could be more than one kind of Higgs particle, which ones?
What if them are found?
Could an arbitrary universe exist without the Higgs field? or it would exist as a it must exist? (maybe this is very philosofical)
What...
I am studying general relativity from Hobson and came across the term 'lifetime' of a closed (k>0) universe, ##t_{lifetime}##.
I suppose at late times the curvature dominates and universe starts contracting? Are they simply referring to ##\int_0^{\infty} dt##? If so, would the bottom expression...
Homework Statement
(a)Find how ##\rho## varies with ##a##.
(b) Show that ##p = \frac{2}{\lambda^2}##. Find ##B## and ##t_0##.
(c) Find ##w## and ##q_0##. What values of ##\lambda## makes the particle horizon infinite? Find the event horizon and age of universe.
(d) Find luminosity distance...
I have thought about something for a while now, and wondered if we would have a different understanding of the universe, and the smallest known particle, if we humans were smaller or larger.
What if we humans was at the size of a pinhead (And maintained the same brain capacity as normal sized...
Homework Statement
[/B]
(a) Find the value of A and ##\Omega(\eta)## and plot them.
(b) Find ##a_{max}##, lifetime of universe and deceleration parameter ##q_0##.
Homework Equations
Unsolved problems: Finding lifetime of universe.
The Attempt at a Solution
Part(a)[/B]
FRW equation is...
I'm talking to a friend here in whatsapp, he says that he believe in a 'dimensionless universe', look what he said... "let's consider that time is an illusion and since time has such an intimate relationship with space, space is an illusion as well". he said that the concept of universal...
There is some surprising twist regarding measurements of accelerating expansion of Universe. Maybe it is not accelerating that fast as previously predicted. It seems that there is something questionable about Ia supernovae.
What do you think about it? Is this real game changer or some minor...
Nothing can exceed the speed of light so how can scientists can tell us about 1000s of light years away of our location in the universe ? I mean what instruments have they used for it ? Waves? ( what kind of waves ? ).
Starting from the FRW metric (for simplicity flat space, radial direction only):
$$ds^2=-c^2dt^2+a(t)^2dr^2$$
If we take dt=0 then the proper distance ds(t) between two spatially separated points at cosmological time t is given by:
$$ds(t)=a(t)dr$$
Now at the present time t_0 we can define...
This is a follow up to another thread (https://www.physicsforums.com/threads/something-about-calculating-the-age-of-the-universe.807250/), but I post it as a separate thread since it is not clear to me (a) this is actually correct, and (b) assuming it is, whether it actually provides a...
I think it is correct to say the farthest light we can see is about Z=7' it would be remiss of us to think astronomers will not find light from higher values of Z in the future.
My question is how old IS the univeres.
http://phys.org/news/2015-02-big-quantum-equation-universe.html...
Good day all,First of all, I want to let you guys know that I'm quite new to the subject so please bear with me in case I'm asking a very basic question here. I have a struggle with the way the Age of the Universe is calculated by using Hubble's Law: V = H x D and I hope you guys could clear...
I'm just wondering why there exist objects like http://en.wikipedia.org/wiki/HD_140283 (The Methuselah Star) that have projected ages older than the projected age of the universe itself. That, where does the conflict between the age of these very old stars and the calculated age of the universe...
Penrose wrote in the Road to Reality that gravitational clumping increases the entropy of the universe. The early universe was very low in entropy because it was very smooth, with very little clumping.
So, is it accurate to say that the early universe was high in entropy except for the...
Hi everyone.
I'm almost done with my senior year of university (and will be going to Davis in the fall for the Ph.D. program), and something occurred to me yesterday: the number 3 is very prevalent in our universe. So my question is "Why?"
A few examples:
As far as we can tell, there are only...
I understand that these distances are speculative, but I am given to understand that, at the end of inflation, the diameter of the OBSERVABLE Universe was approximately 10 centimeters. However, the diameter of the UN-OBSERVABLE Universe was a good deal larger, with a diameter of approximately...
Does the universe as a whole ever change from being the universe as a whole? Does it ever break into pieces and cease being the universe?
And if anything (like the universe) never changed its state, wouldn't that mean its entropy never changed? Are there any constant thermodynamic properties...
Guys I know this is absurd, but it kinda makes sense to me. Recently, while i was doing housekeeping, I asked my brother to throw a piece of sponge down. He compressed the sponge and dropped it down. While the compressed sponge was falling, I saw it expanding. Seeing this, I realized that the...
In the Wikipedia article https://en.wikipedia.org/wiki/Accelerating_universe#Evidence_for_acceleration the following equation
(1)
[where the four currently hypothesized contributors to the energy density of the universe are curvature, matter, radiation and dark energy]
is given without any...
In their admirably bold Dec. 2014 paper "Cosmology from quantum potential", Ali and Das claim that a reformulation of General Relativity, using Bohmian quantal trajectories in place of geodesics, tentatively confirms that the universe is of infinite age and had no beginning.
I'm grateful to...
Is it possible that the universe started with a collapsing supermassive black hole that released what it absorbed after eating the entire universe? If so , could it be possible that this an infinite cycle of death and birth of universes?
Hello everyone, i am just bothered by the theory that our universe is expanding, if so i want to know, what substance is filling the void as our universe expands, and where does this substance come from,
Thank you