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.
If I induce vacuum in a glass tube and then I open the lid of the glass tube, air rushes into fill in the vacuum. Can vacuum be regarded as a sort of potential energy, able to exert a force? Can a vacuum tube be considered as a potential storage device for energy, just like a container filled...
From this link
https://en.wikipedia.org/wiki/Fine-tuned_Universe
It seems that it is, what is the probability for such a universe?, has it gone through many iterations to come to be able to support life,? or was it a that life can be able to flourish or adapt to manifold of universes , for...
I know that quarks can never exist in isolation, and also group up so that they have a net neutral colour charge. But I am wondering at the start of the universe, or under very, very extreme conditions (such as the start of the universe) would quarks have been able to exist by themselves. I have...
I can't be the only person to ever have this thought so I am hoping one of you star gazers can tell me what I am missing. I understand Hubble's theory and the idea of space itself expanding. My question is this. If we know the universe is expanding because of the redshift and the farther away we...
Really good blog post by Sean Carroll on a shockingly common misconception:
http://www.preposterousuniverse.com/blog/2015/10/13/the-universe-never-expands-faster-than-the-speed-of-light/
Hopefully at least scientists will stop spreading this misconception soon.
After learning a bit from the thread "The Dark Sky Ahead", I have tried to think through the dynamics of gravitational interactions in a simplified scenario. Unfortunately the GR math of the problem is over my head. My attempt below, using a simpler approach, leaves me quite confused.
If my...
Hello I have question about universe density so is there any equation what says how to calculate universe density because on meany cosmology equations:wink:.
I know this question is quite odd as we're still researching on this, but is the universe speeding up, aka, accelerating? Or is the speed constant? Or is it slowing down?
Thoughts?
(PS - I don't know what the prefixes B I A means, I have chosen a random A, please consider if it's wrong, am...
As the universe expands, space itself gets "stretched" and objects drift apart, like dots on elastic surfaces when force is applied. So one meter billions of years ago is two meters today, but does it necessarily mean light takes twice as long to travel this "new meter"?
Homework Statement
Assume that in an alternate universe, the laws of physics are very different from ours and that "ideal" gases behave as follows:
(i) At constant temperature, pressure is inversely proportional to the square of the volume.
(ii) At constant pressure, the volume varies directly...
I'm just beginning physics and teaching myself classical physics from an intro physics textbook and in the 2nd chapter it described reference frames. This got me thinking. My reference frame is the earth, as that is what I use to describe position, displacement, ect. But what is the reference...
my wife asked me after watching firefly, "how big is the actual universe?". I actually had no idea at the time and I was too lazy to get up and research it but I did have a calculator on my desk and a pad of paper so I wrote this. The actual size of the universe itself? I'm not sure of, but...
Would it always be identical?
Would it ever be identical?
Essentially with the current state of physics and taking quantum fluctuations into consideration, would it always be the same?
Is there motion at T=0?Another question:
If we restarted the Universe from the big bang and let it play out...
Celeste: A new model for cataloging the universe
The roots of tradition run deep in astronomy. From Galileo and Copernicus to Hubble and Hawking, scientists and philosophers have been pondering the mysteries of the universe for centuries, scanning the sky with methods and models that, for the...
Hi,
We all know the universe is expanding and it's doing so at a rate greater than the speed of light. But what does expansion mean? Popular Science videos usually give the loaf of bread example expanding in the oven. But even the loaf of bread has limits, it can only expand so far. Do we know...
How are we, and the universe effected from its accelerating expansion? Also how will our perception of the world around us be effected, since the universe is expanding and light is constant? <-Will things appear to move slower? I know that we only experience just a small fraction since the...
I read in "The Theory of Everything" of Stephen Hawking that all of the galaxies are running away from ours.
That made me think that the Milky Way is the center of universe, since each galaxy is running away from us(like waves on the surface of water centered at one point which is the Milky...
Hello, I've a problem.
I need to find the age of universe in normalized Planck units. In my case, I'm using Planck mass = 1 and:
##H = 1.18 × 10^{-61} \times t_P^{- 1}##
With these values, how can I find the age of the universe?
Thanks!
Hi PF members, I have a question about electromagnetic radiation propagating in an expanding universe.
We know that because of space expansion, light from a distant source gets redshifted, its wavelength becoming longer and its amplitude flatter.
If we move far enough from the source, we...
Why in ZC (ZFC-reemplacement+separation) can´t exist Von Neumann Universet not even till \omega2. Sorry, I am new in the forum and I dont´know use Latex
According to Einsteinian Relativity, is the Universe considerably younger if one was to view it from within a greater distortion of the gravitational field? Is the value we assign for flat or non-flat universal age dependant on our own point of reference for time?
So, as I understand special relativity, when you go close to the speed of light, observers see you "shrink" in the direction of motion, and you see objects as shorter than they were when you were in the same frame, according to L=Lo√1-v2/c2.
So suppose I am nearby Earth (in the same reference...
Hi All,
I stumbled across these forums while googling for peoples thoughts on this question. I see that this similar question has be asked before some years ago, and I wanted to get current opinions and ideas on the following. I wonder about this and many of the mysteries we seem to...
If digital physics is true and physical reality consists of computations, then what could possibly be the computational platform, i.e. where could the computations be run on? What are possible answers explored in digital physics?
there are no electromagnetic waves? All I know is that there is a modified version of the Maxwell equations (in differential form) for such a universe, such as (the arrows represent vector arrows):
→∇x →B = μ0 →j + μ0 ε0 ∂→B/∂t instead of having ∂E/dt in the last term (which would be the case...
Is it 'possible' (that is, if you say not, can you conclusively show the negative), that the entire observed acceleration in the expansion Our Universe, created some 13.7 x 10^9 years ago in the Big Bang, is due solely to centripetal force throughout, caused by a complex...
consider two concentric spheres, where inner radius is r and outer radius is r+delta. Assume space between the two spheres is mass of an amount to be solved for. Given the metric inside the sphere, assumed to be varying as implied by the Cosmic Background Radiation anisotropy (CBRa), can the...
This isn't too much of a question, but more of an open proposal.
Now... to begin, I know that both you, reading this, and I can agree that our universe is expanding. The universe is expanding from every point within itself, there is no Defenitive reference point, this is a fact.
So for an...
As opposed to antimatter, that is. The whole search for the asymmetry of matter vs antimatter seems to rest on the implicit assumption that what we observe is matter, not antimatter, no?
Is there a way of distinguishing from afar between the two?
I'm new to this impressive forum and have a question that may have been addressed a thousand times, but here goes.
A FLRW metric is happy with a time-varying scale factor a(t) and zero curvature parameter k and could care less about density. The combination of a FLRW metric and the Einstein...
[Moderator's note: Spun off from another thread, where it was off topic. Please start a new thread when you have questions on a new topic.]
Photons lose energy when they travel long distances. Where does that energy go? What happens to that energy? Is there any theory regarding this?
Dear PF Forum,
I have a simple and cliche question.
What is the edge of the universe?
1. We live on the surface of the earth. It's 2 dimensions against Earth 3 dimensions.
If we start from Equador which lies on the equator to the east, we'll reach Columbia then Brazil then Atlantic ocean...
if parallel universe are real... means according to schordinger equation..many possible states..then when we chose anyone state..then other options or i mean possible states would dissolve into one single option whom to chose... or remains present as a reality...?
Hello everyone!
I've been having trouble regarding the age of the universe and another small problem. This problem escalated when I first started reading Dr. Brian Greene's book "The Hidden Reality". The distinction between the two possibilities, that our universe is finite or infinite, plays...
The Universe is constantly expanding, and from the observation of Hubble, super novas, the figure turns out to be a acceleration. The theory that's most accepted seems to be dark energy at work.
As the story goes, before big bang, there was nothing, maybe not even time or space, so how does...
I have very little understanding of the Big Bang, but it seems like it would require a finite universe even though there seems to be a scientific consensus that an infinite universe is a strong possibility. How are these ideas compatible? If space started expanding from a small point at a finite...
Space is expanding, which separates objects from each other in space. Won't this add potential energy? Doesn't this violate the law of conservation of energy? But if it does not, how can space be added without adding potential energy?
I understand that Gott derived a formula for calculating the size of the observable universe, and the value of the diameter based on current obsrvations is 93 Gly. Can someone please show the mathematical derivation of Gott's formula, or give a reference to a source which shows this derivation?
How the scientists are determining that a galaxy exist & many galaxies also there. How they find the universe? without seeing with our eyes, a human being can never ever judge the things. but in the existence of other galaxies & universe how they came to conclusion by the telescopes & advanced...
Dear Friends!
Probably more than a decade back understanding tells us : If the average matter density of the universe happens to be smaller than a critical value,then the galaxies will never come to a halt and turn back(Open Universe).Which will imply cold and lonely death.
If on the...
If I imagine an interplanetary fight between two early races (the universe is about 8 billion years old) and one of them invents a super weapon to extinct the other. The weapon is a grey goo weapon, a swarm of billions of machines, each with the ability to bend light around it to cloak itself...
I saw a video by a physics writer who said that the beginning of the universe was like digging a hole: the hole and the pile of dirt cancel each other out. This of course means that the ground, so to speak, before the digging was zero. But where is the "hole" once the universe began? I asked...
Homework Statement
Can we consider the universe to have a uniformly charged distribution?
If so, shouldn't the field at any point in space be zero? Since the universe is infinite, will it be symmetrical about any point, field should be zero right? Why is this not true?[/B]2. The attempt at a...