Universe Definition and 1000 Threads

The universe- from our understanding, is expanding, thus the regions (for lack of a better word) particles have not yet reached do not exist. How far our universe can/ will expand is unknown, it may be infinite, but we can conclude at this time, as it is still expanding, that it is finite. True...

I'm just being introduced to quantum mechanics and physics, and I was wondering if the possibility of a parallel universe could exist. And if so, how do we know? I read some articles about the research done with Australian researchers who theorize that parallel universes do exist and interact...

Anybody knows this book : The refrigerator and the Universe ? Is it any good ? And what is the level required to read it? Thanks

Do professionals use the term universe to mean what was created in the big bang?

Does the universe have a literal centre (i.e. a physical point in space where the distances to the edges of the universe in all directions are equal)? Assuming the universe isn't infinite, which would make it far easier to understand that it doesn't have a centre, or is a 2d sphere like the skin...

We already observed it; it's too late to say it is too improbable. A particle from a star that exploded billions of years ago just went into my glass of water. But, if we ask the question before our sun blows up if a specific particle from it will land on the highest point of a planet 50 light...

If reality requires an observer, and life on Earth is only 3.8 billion years old- yet the universe is 13.8 billion years old, who was the observer for the first 10 billion years?

A significant number of physicists today postulate that the universe we reside in is infinite in size. It's also thought that if we extrapolate back in time to the big bang that the universe was a singularity of infinite density. Singularities are commonly thought of as a dimensionless point...

I thought of something interesting just today. Let's say I have a decision to make, left and right, that will lead to different future. The idea is, there is a universe where I choose left which have different future than if I choose right, in that sense I have no problem. However, in order for...

@mfb mentioned in a thread about dark matter how neutrinos don't conglomerate in galaxies and it got me wondering where they are. Considering that they move at nearly the speed of light, I understand why they couldn't be captured by galaxies, but what about large scale structures? Do neutrinos...

In a recent thread I incorrectly stated that an observer moving at a high velocity relative to a co-moving observer would measure the age of the universe as more than the co-moving observer would. Apparently that is incorrect, and the age of the universe measured by the first observer would be...

I am assuming scientists say that the universe is 13.8 billion years old with respect to time on earth. If so, how come the infinite energy present at such a small scale didn't make gravitational time dilation infinite during the first stage? Wouldn't time dilation make the universe infinitely...

How can the age of the universe be determined when there is no absolute measure of time or distance in the universe. Every other place in the universe has another rate of the passing of time. Since time expands with the expansion of space, trying to use expanded time to measure time is circular...

Is it true that the speed of light is only dependent on the size of the universe, if the universe were much smaller would the speed of light be faster?

i have a question about the motion of galaxies and the speed limit of light. using Hubble's law, it is theoretically found that after a certain distance(about 4200 mega parsec or something) from a observer, the galaxies are moving faster than the speed of light. consider the following...

What is known about how long it took to transition from an opaque universe to the release of the cosmic microwave background?

Homework Statement Two scientists detected the cosmic microwave background radiation at a frequency of 160 GHz. What is the temperature of the universe? Homework Equations peak wavelength x temperature = 2.898 x 10^-3 c = f x wavelength The Attempt at a Solution I calculated the wavelength of...

[Moderator's note: thread spun off from post in a different thread quoted below.] That seems to me a rather extraordinary claim. Could you demonstrate how for instance cosmological redshift can be explained in a coordinate independent fashion?

I am not sure if this is true, if it is can these black holes be the dark matter we have been searching for. https://www.sciencedaily.com/releases/2016/06/160622144930.htm Date: June 22, 2016 Source: Rochester Institute of Technology Summary: Astronomers have presented one of the most complete...

Hi, I don't have any degree in physics whatsoever, but my question is about a dream I had. My last thread got locked when someone got arrogant with their degree or knowhow (and the lack of mine), I'm hoping you would think "outside of the box" with this one. Don't take it as a dumb dream right...

Hi, I don't have any degree in physics whatsoever, but my question is about a dream I had. Not to identify a meaning to my dream, but I want to know from YOU who are may be specialized in this following field: I often dream about space, be it me spacetruckin through the cosmos, aboard ISS or...

In thinking about force symmetry and conservation laws, I think I am right that the total amount of color charge and electric charge in the Universe is conserved, but is gravity conserved? does a Universe at maximum entropy have the same gravity as one say, just after the big bang? Thanks, Mark

My question perhaps is assuming there is a multiverse, but its more of a mathematical question. If the universe or universes have existed forever, will the number of days that have been be a countable infinity or uncountable? Thanks

Homework Statement [/B] "Direct addressing is a simple technique that works well when the universe U of keys is reasonably small. Suppose that an application needs a dynamic set in which each element has a key drawn from a not too large universe U. We shall assume that no two elements have the...

Just what would a universe be like if it had two time dimensions?

Does anybody know of a resource that I could use to determine the density of the universe along a specific line of sight? (right ascension and declination)I am investigating inertial forces and looking to identify both the most and least dense directions in space and determine by how much they...

multiple_authors submitted a new PF Insights post Where Did the Big Bang Happen? Continue reading the Original PF Insights Post.

Here they use information gathered form Cepheids, are these parallax measurements accurate? From science daily. Date: June 2, 2016 Source: Space Telescope Science Institute (STScI) Summary: Hubble Space Telescope astronomers have discovered that the universe is expanding 5-9%...

Reading the Wikipedia article makes my head spin! Somehow the figure https://en.m.wikipedia.org/wiki/File:Observable_universe_logarithmic_illustration.png doesn't seem quite right. I don't understand how the CMBR doesn't define the edge of the universe. If we can see the CMBR that happened near...

If vacuum energy has a non-zero value, is the vacuum energy density (vacuum energy over a given volume of void space) being reduced over time due to the expansion of the Universe? If so, is there any consequence on the particle-antiparticle creation/annihiliation process? Will there ever be a...

if the uverse is expanding and known to be accelerating, at what rate is this acceleration? even at small # over the billions of years, would it not be at speed of light already, and if so, how would observable mass be traveling at the speed of light?

According to the paper they used 300 SNe Ia along with Cepheid variables, as a basis for determining cosmological distances. With the exception of 19 SNe Ia, which were calibrated using nearby Cepheids, the remaining 281 SNe Ia were based purely on their light curve to determine their type...

I read here, http://www.space.com/24781-big-bang-theory-alternatives-infographic.html , that, "What we call the "observable universe" (or the "Hubble Volume") is the spherical region, about 90 billion light-years in diameter, that is centered on any given observer. This is the only part of the...

If there is enough gravity and the universe starts to collapse in on itself, would life forms that live during this phase of the universe get younger as time passes and they would need to expend energy to stay old?

I was discussing with some friends the other day. We were philosophizing about a hypothetical universe which is governed by the principles of causal determinism. (Go look at the Wikipedia page on determinism for more details about causal determinism.) Our first concern was: Could a computer...

It may be that nothing is, or even can be empirically known about exactly how big our universe is, or the shape of its geometry (flat, round, etc.), but what are some basic, provable facts that can be used to work out a theory or to debunk one? I know this is a very broad question. I have come...

I know this has come up before but there is still something puzzling me about the whole BB paradox. This is the problem phrased in the context of our evolving universe. As far we can tell the universe will expand forever ( assuming dark energy is not something variable but is a constant). In a...

The universe is expanding at an accelerated rate. Space has no edge. If space is geometrically "round," meaning that a long enough journey could bring you back to where you started, then it could be said that the universe has no outer edge. At the moment of the big bang, the universe created...

Could there be outflows associated with the poles of a universal black hole? Could the pressure associated with the black hole’s dark energy emission cause particles of matter to form and accelerate outward? Is the timeline the time and distance from the black hole? Is this the cause of dark...

Suppose the universe is infinitely big, then even the most improbable thing will happen somewhere in the universe, in fact it will happen an infinite number of times. So what we consider to be probable things and what we consider to be improbable things are both infinite. So how do we rule out...

Faster-than-light communication is not allowed in this universe. Imagine a sister universe that looks much the same as ours but allows instant communication between any two points. In that universe, simultaneity can be established using instantaneous communication. How would that affect our*...

Hello and thank you in advance. I'm writing a hard science fiction story and part of it is how humanity is spreading throughout the universe. What I was wondering was, can anyone explain to me the equation needed to answer this question so the story can have it's realism? In the near future...

https://www.sciencedaily.com/releases/2016/05/160512142915.htm A faint blue galaxy about 30 million light-years from Earth and located in the constellation Leo Minor could shed new light on conditions at the birth of the universe. Astronomers at Indiana University recently found that a galaxy...

i opine that the universe is not 3 dimensional at all. its not build up of 3 coordinates at all. it is because, we humans could see 3 dimensions it doesn't mean the space metric is of 3 dimensions. suppose there's a super being living on an Earth like planet of some other galaxy whose viewing...

A friend and I have been debating a topic for the last few days and I would really like a more informed opinion on the discussion. My friend says that IF you could, some how, see the universe from the outside and it appears that the universe is a finite flat, spherical shape, or other shape...

Hi all, I've just been having an interesting pub conversation with (what I would call) an amateur cosmologist and I posed the following question "the observable universe is stated as being c 50 billion light years wide but (even putting aside issues such as expansion / contraction) if nothing...

Hello, everyone I am new to the site I was wondering if the Universe and gravity are types of fluid? As you can read I am not a cosmologist or even a physicist but I love science

Apologies if this question has been asked already. I've been given resources to help me understand, but it's been hard for me to wrap my head around the answer and, for that matter, it is difficult to understand a text when you have to look up every other word (an exaggeration, but you know ...

Hi I have two novice question If the universe is expanding and it is all moving apart, how is it that galaxies are colliding? If our galaxy and all others are moving away from some singularity central point. And as we see other galaxies moving away from us at a speed relative to there distance...

So CMBR points to a flat universe, and this seems to be the generally accepted model. But in a flat universe is expansion not supposed to slow exponentially, stopping after an infinite time? How does this fit with the observation that distant type Ia supernovae show the universe's expansion to...