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.
Hello.
I've been doing some reading about Friedmann's three types of GR solution that yield closed, open and flat universes. I think I can grasp the closed solution best. As far as I understand it a closed universe is finite in both time and space. It begins, grows and then collapses in upon...
I don't know this question makes sense or not but;
Respect to the two possible size universe models (finite and infinite) how would be the evolution of the universe without the cosmic inflation?
As we know the universe is expanding. Could this accelerating expansion contribute or cause black hole evaporation given that the strength of the gravitational force does not depend directly on time, while the distance of two given points in space increases with time?
Sorry if my approach is...
After reading the wikipedia article and looking at many other threads on this forum I am still having a hard time understanding the difference between the Observable universe and the entire universe...
Why is the entire universe not observable to us?
The Big Bang happened 13.8 billion years...
In a holographic universe model, could our 3D universe be encoded in 3D and still be a holographic universe, instead of 3D information encoded in 2D space? Or is the standard model (non-holographic) of the universe already 3d information encoded into 3d space...
There are couple things that keep me questioning about the nature of the universe.
Let me start from the begining.
Big Bang happened and our universe was created, and from now on let us suppose that the universe is infinite in size. Later on, the universe expands and after a time we can see...
How can the universe keep on expanding if it's infinite? Expanding metal, like a cube of aluminium, has a surface area which forms a border for the matter contained inside. So the universe must have a border for the matter it contains.
Is there a possibility that we create a wormhole sometime and switch between universes?
First of all what is required to make a wormhole?
What will happen if we made a wormhole?
What proves that there are many universes and that we can switch between them??
Greg Bernhardt submitted a new PF Insights post
This article is part of our student writer series. The writer Arman777, is an undergraduate physics student at METU
A Journey Into the Cosmos - FLRW Metric and The Friedmann Equation
Continue reading the Original PF Insights Post.
So recently I saw a video with Richard Gott explaining a self-creating universe. There's three quick questions I'm confused about that I did not understand very well from the video:
1. How does a closed time-like curve allow the universe to self-create? Wouldn't the universe just go around the...
Dear All
I know that my question is not so related to this, but i will appreciate any answer. Why could we have 2 different models for the universe ( one expanding, collapsing...) although both are receiving the same experimental data... I need to write an essay about this topic. I have ideas...
What if there is a universe with just one point charge in existence....just a charge with vast emptiness around it....now here all laws of physics remain same...
But is the concept of field and energy defined there??
Greg Bernhardt submitted a new PF Insights post
Coordinate Dependent Statements in an Expanding Universe
Continue reading the Original PF Insights Post.
Hi, I am new here. A while back I read articles about observations of supermassive black holes in the early age of the universe. What are the hypotheses that would explain how these black holes grew so large and so fast so soon? Could inflation play a role here? Like how inflation would be able...
It may sound stupid but something bothers me and I want to ask
This question come to my mind due to another thread,
https://www.physicsforums.com/threads/entropy-and-derivations-is-my-logic-faulty.935533/page-2#post-5910474
In Friedmann Equation we are assuming that universe is homogeneous and...
Hello. I am starting to learn about thermodynamics. (i'm going to use lower case "d" for delta)
Energy is neither created nor destroyed. So dU = 0 for the universe as a whole.
If the universe is constantly expanding, then it must be doing work on the vacuum around it, right? So W is a...
Hi,
I am quite confused about followed question,
I think scientist think the last scattering surface was dense plasma at the temperature of 3000K. If the today's universe much cooler and less dense then "the last scattering surface" how can anyone says entropy increased by time? Isn't universe...
If the universe suffered a false vacuum decay, would this change physical laws? Could it change the universe so much that it would allow our universe to be a multiverse of level 1, 2, 3 and 4?
https://en.wikipedia.org/wiki/Multiverse
This has been a real famous analogy and I understand it, except the fact that the balloon surface is a 2D structure. How is it possible to depict a 3D universe on a 2D plane ? What happens when we work with stars at multiple planes ?
This may sound like a noob question but please help me out guys.Will universal acceleration ever retard ? And if it continues to accelerate for all eternity, where is it getting this never ending energy from ?
I am trying to read through this paper discussing what quantum fluctuations mean in their various contexts, particularly in de Sitter space. I have come across this passage and am curious to what it actually means?
https://arxiv.org/pdf/1405.0298.pdf
pg. 10, second paragraph:
"If a quantum...
Does the presence of the cosmological constant modify the rate of expansion of the universe even during the earlier deceleratingly expanding phase of the universe?
Normally when one is asked what is the universe expanding into, the answer is its not expanding into anything. Space itself can expand. However In the context of eternal inflation, our universe is a bubble in a sea of inflating space. And hence assuming eternal inflation is right, does the...
I understand that there are roughly ##N=10^{79}## nucleons in the visible Universe. This number comes from adding up the nucleons of ##100## billion stars in ##100## billion galaxies in the visible Universe i.e.
$$N=\frac{10^{30}}{10^{-27}}. 10^{11}.10^{11}=10^{79}$$
where mass of sun is...
I have a question regarding the process of getting towards equilibrium in our universe. If we imagine a causal patch with our planet at the centre, every planet will redshift away from us an after a while the planet itself will disintegrate, let's call this process the decay of Earth. Eventually...
It explains very well many aspects of the Universe.
Why should there be any angular momentum though?
The idea that the Universe is itself intrisically rotating doesn't make sense.
Some theorists have put forth the idea of an atemporal universe - ie. a universe without time - claiming that time is an illusion or abstraction created as a placeholder for what is really entropy.
https://phys.org/news/2011-04-scientists-spacetime-dimension.html
So they're claiming that...
Is knot theory taken seriously by the sconce community , This seems to be a novel theory which explains why our world is three dimensional.
https://www.sciencedaily.com/releases/2017/10/171016190308.htm
An international team of physicists has developed an out-of-the-box theory which proposes...
do we know for a fact that the gravitational constant has always been the same since the dawn of the universe? I feel like gravitational forces should slowly be decreasing as the universe ages (meaning that assuming mass of Earth doesn't change, we should weigh a bit less in a billion years)...
Now two points here. (1) Most Cyclic Universe theories I've heard require the universe to reverse course and fall back into a Big Crunch to recycle again. Now that Dark Energy has been discovered, the chances of a Big Crunch have gone away. (2) Some theories suggest that the universe started...
Hi all
I read a question on this subject from some time ago but was not satisfied with the clarity of the answer and in the light of recent experimental results I wish to clarify my understanding of this ancient scientific question.
What is the cause of Inertia?
So is inertia simply the total...
Are there any indications on how large the universe might be? Not the observable universe, but the universe which came into being 13.8 billion years ago and of which our observable universe is a part?
It is said that the imbalance of matter versus antimatter in the present universe implies CP violations at very high energy. It seems to me that it most directly implies baryon number nonconservation: If we assume (and I'm not exactly sure why this is a necessary assumption) that immediately...
The article Spontaneous creation of the universe from nothing (Dongshan He, Dongfeng Gao, and Qing-yu Cai) published by the American Physical Society discusses a mathematically proof that the universe could be spontaneously created from nothing using the Wheeler-DeWitt equation (pictured below)...
Hi all,
Yet another question: if the universe is finite, then linear momentum should be quantized (I assume in a similar manner to an infinite potential well since there are boundary conditions). My question is, then, if one computes a value for ##\Delta p## (momentum variance), is the variance...
My question has multiple parts, does the following paper:
https://arxiv.org/abs/1405.0298
Disprove the possibility of creation of another universe through quantum fluctuations if heat death occurs?
If it does could another universe still be created through quantum tunneling?
Can quantum...
Greetings! I'm new here and I think about this place as soon as I see what the statement asks.
Homework Statement
Considering the volumetric density ρv=(e-2r/r2), figure the total charge (ℚ) of the universe.
Homework Equations
[/B]
ρv=ΔQ/ΔV -> (ΔQ ∝ ΔV)
ℚ=∫v ρv dxdydz
The Attempt at a...
I've seen numerous descriptions of inflationary phase a-la "The universe was supercooled from about 10^27 down to 10^22 kelvins".
However, I do not understand what is the basis for such estimation. We do not even know with any certainty how long the inflationary phase lasted. For one, "eternal...
In a dark energy dominated universe, it seems that all the particles get away from each other and that the final state will be one with one or zero particles per horizon. This sounds very intuitive, but it is based on classical physics and GR. Particles have wavefunctions and this is whar...
This may sound like a noob question, even more if it's asked by a undergraduate physics student, but here it's:
How do we know about the existence of 100 billion galaxies out there (even that it's an average value)? I mean, how do we know about these exact number? Why not, say, 200 billion or...