# Tag Info

## Hot answers tagged universe

10

The "catches" as you call them are at least threefold: Cellphones require transmission and receiving hardware that fit in your hand / desktop computer and be almost omnidirectional, i.e. able to receive transmissions from any direction. In contrast, deep space probes are tracked with extremely directional, huge antennas of hundreds of meters diameter ...

7

If you're asking whether there is any chance we'll be able to do this in the forseeable future then answer is no. If, however, you're asking whether general relativity allows constructions like this then the answer is yes. Your question refers to a brane which would exist inside a bulk of our own design, and I don't know how literally you meant this but it ...

4

Okay, let's start with the basics. The Big Bang was not like an explosion in space from which spewed all matter in the universe. The Big Bang was a moment in time. We have this thing called a spacetime metric. I won't bore you with the details, but essentially it is the equation we use to describe all of the geometry in the universe. It includes all the ...

3

We all know that energy is never lost, but it transforms into another form.  Actually, in General Relativity it is possible for energy to change. But energy is also frame dependent (in any theory) and there is no obvious frame in General Relativity in general. Doesn't that mean that energy is not unlimited? No, even if you used Special Relativity ...

2

Photons (radio waves, "light", gamma-rays, etc.) and neutrinos contribute negligibly to the total energy density of the Universe. By far, most of the photons that exists today are the cosmic microwave background, with 450 photons per cm$^{3}$ (e.g. Hobson et al. 2006). The number density of neutrinos is similar, 330 per cm$^{3}$. In total, the energy density ...

2

I think you have a fundamental misunderstanding of what the heat death really is. Any observer, whether they are a time traveler, observer from another universe, or whatever, would just see a lot of empty space. The first thing to know is that the heat death is not a single event. The universe, after heat death, is dead in the sense that nothing is ...

1

Lie down and fall asleep. Right on the razor's edge between awake and asleep, look at what it all looks like. See yourself and the world in unison, fading away... slowly, and at the same time instantaniously. Then, in the morning, be thankful that your experience was merely that of falling asleep, and not a more permanent heat-death. (The question is ...

1

The number of atoms in the universe is not known to be infinte or finite. The biggest problem is that we cannot see all of the universe. The universe is only 13.8 billion years old, meaning that we can only see 13.8 billion light years in any given direction. This portion of the universe, usually called the "observable universe", has been estimated to ...

1

The hubble relation is: $$v = H d$$ where $v$ is the velocity of the galaxy relative to the Milky way, and $d$ is the distance of the galaxy relative to the milky way. The velocity is measured using redshift. The distance is measured through a complicated series of standard candles, along with the relationship $I = \frac{I_{0}}{4\pi r^{2}}$. If you ...

1

Firstly, string theory is a mathematical hypothesis that is currently speculative. It is a possible candidate for a quantum theory of gravity - a unification of QM with Einstein's theory of gravity - General Relativity. The idea of superstring theory emerged from another theory called supergravity. Supergravity was an attempt at a supersymmetric theory of ...

1

There are probably duplicates/variants of this question on this site. Expressing the problem in mass terms seems a bit odd to me though, as it's been put in energy terms every other time I have seen it asked, unless I have misunderstood your question. Here is an answer (to an identically worded question) based on the link: Predicted Mass of Quantum Vacuum ...

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This seems to be still very much a mattter of opinion, based on the excerpt below from Space.com, which sums it up nicely and which you may already have read. Lots of questions currently with not enough data to resolve, esp. with regard to dark matter and questions regarding the first stars. Fingers crossed that LIGO and the JWT give us a clue in the ...

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