Universe Definition and 1000 Threads

honestly just need some help here i understand the physics just not how to code it or the syntax of python

In the wikipedia article of the observable universe I have read the following: "Both popular and professional research articles in cosmology often use the term "universe" to mean "observable universe". This can be justified on the grounds that we can never know anything by direct...

Over the years the following has continued to be my biggest question in Cosmology. In the past couple of years I wondered if we have got any closer to understanding whether our space is infinite or infinitesimal? (By infinitesimal I mean that there is no lower limit to the minimum separation of...

The Hawking-Hartle no boundary condition is well known. The authors considered a many worlds/histories model considering a sum over all compact euclidean metrics. But are there any models or theories that consider a sum over all possible metrics or boundaries? And finally, if all possible...

I have often read that dark matter and dark energy are now thought to comprise 94% of the total mass of the Universe. Just now I was reading an article which says that dark energy comprises 74% of the total. So, I'm confused about how energy can comprise mass. Dark matter, I can understand -...

Are there any models, theories or physicists who propose that the fundamental laws of nature come from the initial conditions? Are there any physicists who propose that the most fundamental laws of physics emerged from initial conditions at the origin of the universe? And according to this view...

In contributing to the thread https://www.physicsforums.com/threads/i-need-recommendations-to-read-about-physics.996304/ , I see that the video that greatly influenced me to study relativity is now available online on YouTube (made available by the film distributor). In 7th-grade, after...

The Block Universe Theory, based on Einstein's Relativity, says that past, present and future exist at the same "time", the universe is static, eternal, and things doesn't change, movement is an ilusion because you have memories from the past. But if the universe don't evolve does this imply...

Hello! I don't know much about this topic so I apologize if my question is not very clear. I understand that one of the conditions required to explain the matter-antimatter asymmetry in the universe is to have CP (charge-parity) violation. We have CP violation in the standard model (SM), in the...

By Classic Coulomb's Law there exists negligible yet non zero force of attraction between two unlike charges in-spite of the distance. However for electrostatic attraction to work we need at-least one Faraday Tube(Lines of Forces) between the attracting charges, does that means...

How does the Singularity produce all of the diverse matter and properties that we observe in the Universe today? Although Theories like Quantum Gravity have somewhat produced indications about the existence of Graviton particles and allow some form of Gravity to operate within the laws of...

Why does the term observerable universe have any meaning outside of observers on earth? From earth, the observable universe is the universe 13.8 billion light years away in every direction which is large but a finite distance. Say there's a galaxy near the edge of our observable universe...

Cumrun Vafa and colleagues have recently posted a new theory of the early universe in the paper: https://arxiv.org/abs/2009.10077 If anyone could explain the main themes of the paper in laymen friendly manner that would be really appreciated. In particular what is topological gravity ? how is...

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...

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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...

The cosmological principle seems to hold well, and would imply an infinite amount of matter in the universe if the universe is flat and unbounded

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...