Universe Definition and 1000 Threads

According to the theory of relativity the speed of light is the cosmic speed limit which means(I think) nothing can go faster than the speed of light.Then how universe can expand faster than light itself?

The top and Higgs mass determination arose the old discussion about electroweak vacuum metastablity. There is an interesting fact that with available data the universe places in the edge of stable and meta-stable zone tends to be inside the meta-stable region. This conclusion confirms up to...

I wrote an article about the idea of a donut-shaped universe. Not insightful enough for an Insight, but I hope you enjoy. http://klotza.blogspot.com/2016/01/the-simpson-hawking-donut-universe.html

So if the universe expansion is accelerating due to dark energy, does that mean that (assuming there is) one end of the universe relative to the other end of the universe will see it moving away at speeds greater than the speed of light? Or is the expansion capped by relativity? Or does the...

In the absence of a cosmological constant, there is a critical density (in the FLRW model) at which the universe expands asymptotically to zero velocity. If the density of the universe (without a cosmological constant) is above that critical density, at some point the expansion reverses and...

I want to get this simplest cosmology question asked once and for all because I don't get it. We have "cosmologicial models" which have the curvature of the universe going from positive to negative ( or maybe visa-versa ) at some stage ( or not? ). Now elsewhere we hear that a negatively curved...

OK I might be stupid and english isn't my native language, so I'm sorry in advance. So: The red shift is bigger, the further away a galaxy is (they move away faster), and the closer it is, the shift is smaller and it goes to blue for Andromeda (towards). Everyone knows that. BUT When you...

Just thought i would flag this up. arXiv:1601.01701 [pdf, ps, other] A 6% measurement of the Hubble parameter at $z\sim0.45$: direct evidence of the epoch of cosmic re-acceleration Michele Moresco, Lucia Pozzetti, Andrea Cimatti, Raul Jimenez, Claudia Maraston, Licia Verde, Daniel Thomas...

When we look at the world around us our minds create a three dimensional representation of the world based upon our sensory input, but how do we know that there aren't in fact more dimensions from which we either receive no sensory input, or from which we receive input, but our brains and our...

I have on several occasions on PF flagged up examples where it appears that there is an age problem in the early universe, in other words highly evolved objects have been observed whose existences are difficult to explain at their high red shifts in the standard \LambdaCDM cosmological model...

I understand the basic theory of E Folds, but how was it discerned regarding our universe?

A singularity is a region in which the curvature of space-time becomes infinite. But according to standard big bang models, at the initial point (at which T = 0) the pre-expansion space - as miniscule as it was - was filled uniformly with all energy that ever existed or will exist. But if all...

Well I'm just a high school student but I'm very passionate about Astronomy. I usually ask myself that into WHAT is our Universe is expanding if the expanison theory is true ! I'll be waiting for responses..

I know that when we talk about ‘the universe’ we’re normally referring to the observable universe. It is my understanding that the universe is 'one thing’, the only distinction being that part is visible and part is not, yet occasionally when the subjects of size and inflation are discussed...

How does universe expansion work? I thought that the universe was infinite and the celestial corps were getting further distance from each other. If the universe is infinite, how does someone calculate something when infinity is getting bigger? From a reference point? Is the rate of expansion...

I had seen somewhere that Universe is expanding with a speed greater than Light Speed... it really sounds absurd for me... As per my sense, light speed is the universal acceptable speed limit and we can't get back if we reach that speed until any other thing outside the object makes it to...

Hello, I have a very basic question about the expansion of the Universe and it could be that I'm being very stupid here: if the universe is expanding into the empty surroundings as the red shift evidence seems to demonstrate, then surely the universe must be doing work on the surroundings like...

Hey everyone. I know it may sound just wrong, but i just thought about it... if it is true that there are unlimited number of parallel universes. and we have limited probabilities of the way things happen. and that means that all probabilities happen in some universes. My question is: if math...

I've seen various, wildly different, estimates of the size of the Universe. Do we have evidence demanding that the Universe is finite in size? If so, what are the clues that lead us to estimate that size beyond absolute speculation?

Hey PF, Since there are stars that can be powered predominantly (>50%) by the CNO cycle, which requires carbon as a catalyst, and i understand the core temperatures of these stars is about 106 K. Does this mean that stars where the triple-alpha process is dominant (108 K) had to exist and die...

A lot of cranks on the net make a lot of the torus - of course magnetic fields are toroidal - but not space time right? Or could it be - a torus is flat (zero gaussian curvature) which is how we observe the universe to be as far as we have measured it's curvature on large scales - and it would...

Hello, I'm Harry. I'm new here, hope not breaking any posting rules in any ways :) I have a question and would like to ask for some suggestions and information. The question is about general relativity or gravity and structure of the Universe in general; I know there are definitely quite a...

What criteria are, or reasonably might be, used by cosmologists to decide whether or not the assumption that curvature equals zero produces a better cosmological model than one with a non-zero curvature? I read (as best as I could) Section 6.2.4. Curvature, pp 37-39 of...

Good day. I do not know much about cosmology, rather computer science, but the following theoretical question bothers me a little. Some scientists, like Tegmark, Wolfram, Zuse or Fredkin, support the idea that the Universe might be just computation. Computable means that something can be...

If the Universe were not expanding uniformly (i.e., at the same rate in all places), then would different places would see a different Hubble law than we do? And if If the extragalactic distance scale changed, would the Hubble constant change?

I have heard that Feynman and Wheeler briefly discussed the idea of the 'one electron universe'. According to Wikipedia it came up as follows: It wasn't really a serious idea, more a 'thought experiment'. But what interests me is the fact that electrons are literally indistinguishable. Not...

http://phys.org/news/2015-02-big-quantum-equation-universe.html Some people claim that universe has existed for eternity to get around the Big Bang theory. However wouldn't this violate either the 1st of 2nd laws of Thermodynamics which forbid perpetual motion of the 1st and 2nd kind...

Greetings - We speak of astronomical objects as being x number of light years away, which is also a statement about the age of the data. So our knowledge of M83, for example, is about 15 million years old, etc, etc. I'm just wondering why there never seems to be any attempt to move this...

I like physics involving the cosmos. I was wondering what theories are out there that explain how the observable universe is expanding at an increased rate rather then slowing down due to gravity or other variables. I know the dark energy theory that basically states there's a energy that...

The link below is to an 12/2/15 article at phys.org titled: What is the universe made of? Shedding light on the mystery of missing ordinary matter. http://phys.org/news/2015-12-universe-mystery-ordinary.html Here is a quote: Numerical simulations made it possible to predict that the rest of this...

I do not have any education in particle physics, and I am trying to read the paper http://www.helsinki.fi/~hkurkisu/cosmology/Cosmo6.pdf . I would much appreciate some help regarding the specific questions below. The following is from the first page of the article. I gather that g is a count...

Hello, I have recently been very interested in learning about the 4th dimension (well the little we know about it) I have listened and discussed in some conversations about the topic and have a few thoughts and it questions. -From my understanding the Tesseract is a 3rd dimensional Shadow...

Multiple_Authors submitted a new PF Insights post Is the Universe a Black Hole? Continue reading the Original PF Insights Post.

I have a question that I didn't see covered in any book that I read in QFT (I read so far Srednicki which I finished and Peskin and Schroeder which I haven't finished), can the vacuum generate an infinite number of real particles? How do we generate real particles from virtual particles? Is...

I'm trying to reconcile the age and size of the universe. The size of the universe is more than twice the distance light can travel in the time it has existed. Does this mean that the universe is expanding faster than the speed of light or that it did initially and has slowed down since? I...

I am going to state the few assumptions I am making as I ask this question. 1. The big bang was an expansion of space/time rather than a physical explosion, although the general effects seem similar. 2. The universe is not infinite and cannot be if #1 is true. 3. The observable universe is...

I have been thinking about light and i have read that the universe expanded faster than speed of light. So , then why people say that the speed of light is the fastest thing known if people know that the universe expanded faster than speed of light . Also , if the universe could have expanded...

I've often wondered about what happens when you try to add up the potential due to everything in the universe in a Newtonian way, especially in the context of the "Sum for Inertia" which seems to suggest a connection between Mach's Principle and GR in the context of rotation. Today I noticed an...

Hi, one thing always bothered me about the argument on the size of the Universe. If it started about 13.7 bn years ago then how could it possibly be infinite in extent? Once the time was finite its not possible to attain infinite extent - no matter how fast it expands. Also if there was...

Hello all! Recently I watched a TV Series episode, but I didn't catch it from the beginning and I need some help to find which one was it, or any clue about it. The part that I want is about the Scientist guy explaining that things on the observable universe (big picture) seems to be moving...

http://physics.princeton.edu/~steinh/lambda16.pdf In this research article the authors suggest a cyclic universe, specifically one involving collisions of higher dimensional branes (an idea taken out of string theory), could indirectly explain why the observed cosmological constant is so small...

A discussion from another thread Questions re: Matter-Antimatter Annihilation prompts this question since the discussion there raised the point that a zero net charge seems very unlikely. This new thread's title question might be rephrased as follows: If the universe did have a non-zero charge...

Hello Everyone, Back when Einstein was formulating General Relativity his equations just could not predict a static universe. I have read that they actually predicted an expanding Universe. Later Friedmann derived an equation from GR that would explain how an Expanding Universe would evolve...

PeterDonis submitted a new PF Insights post The Block Universe - Refuting a Common Argument Continue reading the Original PF Insights Post.

Dear all, Can anyone give me a time scale/ redshift range as an estimate for the formation of magnetic fields in the universe?

Dear all, The term "big bang singularity" somehow seems to imply that the universe had zero extent at the beginning. But should this really be taken literally? Because if something has literally zero extent, then not even exponential growth over billions of years could ever result in an extent...

Multiple_Authors submitted a new PF Insights post Can We Tell Whether the Universe Is Rotating? Continue reading the Original PF Insights Post.

If any positive energy always has a negative energy counterpart, then nothing ever exists. Am I missing something here?

Hello. I have heard a question that asks..how can the Universe be created from nothing? Would not the answer to that question be understanding what that nothing is? Humans have an idealized notion of what nothing is..which can be far from the 'nothing' that existed at the beginning of the...

1. Imagine a universe where electrons and protons have positive and negative electric charges, respectively. Could an atom consisting of one electron and one proton exist in this universe?2. None.3. My first thought was that such an universe already exists (ours) since an atom with a negatively...