New answers tagged

4

There are lots of ways to make antimatter "naturally". One of the most common is pair production. A high energy photon is converted into a particle / anti-particle pair. For example, a photon with energy greater than about 1 MeV ($E > 2 \, m_\mathrm{electron}c^2$) can turn into an electron positron pair (some more considerations are needed to conserve ...


1

Antimatter, although only in the form of positrons, is produced by many nuclides during the β⁺ decay. I can not get any reliable source, but vast majority of such β⁺ nuclides seem to be artificially prepared in a reactor, so this is perhaps not a truly natural source. Other article, named "Antimatter from bananas" states otherwise. The concentration of ...


1

In 1997 the Hubble discovered a large numbers of intergalactic stars. Others have since been discovered. It is now believed that about 1/2 of the stars in the universe may well be rogue stars that are located in intergalactic space. The AVERAGE density of intergalactic space is still very small, however, because of its immense size.


2

the cutting by universes is a way : to introduce possible new physics for each of these universes without leaving the homogeneity and isotropy cosmological principles, the known constants and the known physics of "our" universe to defer the infinity issue from our universe to a parent structure : the multiverse Homogeneity and isotropy are the main ...


0

I don't really have the background to understand such matters, but this presentation by Alan Guth gave me at least some idea of what it means to say the energy of a gravitational field is negative (which Guth calls a "miracle of physics"). Starting at 0:52:00 in that video clip, Guth presents this thought experiment... ...where it's taken as a given that ...


-1

Since most the universe is empty space The short answer to this surprise is to see that the density $\rho = \frac M V = \frac M {\frac 4 3 {{\frac{2 G M}{c^2}}^{3}} \pi} = \frac{positive-constant} {M^2}$ decreases quickly as the mass increases. Now let's play with the values of size and mass that one can find on Wikipedia and other publications. ...


2

No. Tides are caused by the gradient in the gravitational field. As you get further from the moon, the field drops as $\frac{1}{r^2}$ and the gradient changes as $-\frac{1}{r^3}$. If there is a gradient, then objects closer to the moon will accelerate towards it more rapidly than objects further away from it. The effect of this is nicely illustrated in an ...


0

Gravitational waves can be emitted from a rotating object, but the object must not be axisymmetric. For example, a perfect sphere will not radiate gravitational waves, but a sphere with some sort of bulge may. We can calculate the radiated energy from such a source (see for instance this paper). However, for gravitational waves to have effects on the same ...


0

No actually this is one perpetuating myth about entropy that even scientists themselves (and school curricula) propagate. To answer this and dispel the myth, ask this simple question: disorder with respect to what exactly? Why is a uniform gas disordered than a gas with two phases? Of course a uniform gas has more (another) symmetry, in fact aquires the ...


1

The entropy law can be (comically) reinterpreted like "equilibrium is a state of maximum possible disorder under given physical constraints". So... things keep getting worse until it's as bad as it can get. Intuitively, large entropy means that things look more or less the same (macroscopically) for many different microscopic realizations. When the system ...


0

And if you still need an answer for your speed of expansion (of the universe, because the solar system isn't expanding just by itself), it is measured to be about 74.3 km/s per megaparsec (a megaparsec being about 3 million light-years)


0

Our solar system isn't expanding, because it's bound by gravity. Even though space is expanding, the positions of objects in the solar system stay the same because gravity pulls them back. This is true for all gravitationally bound objects, even galaxies and galaxy clusters.


3

Entropy is not disorder; it is a lack of information. Consider the entropy formula $S = k_b \log \Omega$. Here, $\Omega$ is the number of microstates (sets of particle positions/momenta) corresponding to an observed macrostate (something macroscopic we can observe, like 'the gas has volume $V$ and pressure $P$). What this formula means is that the entropy ...


0

Entropy is a tricky concept and hard to understand. Personally I tend to avoid speaking of systems and phenomena in terms of entropy and/or temperature because they say very little of the dynamics, and I believe dynamical laws are the ones driving the universe. When we hear that systems tend to increase entropy, we are saying there are dynamical laws ...


8

What you are missing is the microscopic definition of entropy, once you know that, you will understand why people say that entropy is disorder. Equilibrium as order First, let's address your valid intuition that equilibrium as a form of order. Indeed, if everything is in thermal equilibrium, you just need to measure the temperature somewhere, and then you ...


6

First of all as stated by Madan Ivan: equilibrium is not order. But you can get certain systems that are in a meta-stable "local" equilibrium (here meaning that you need some energy to move it from there), for example a crystal. These can be highly ordered. Intuitively: if you smack the crystal with a hammer it breaks to pieces. This brings your closer to ...


13

I personally find the terms consistent. Think of the entropy as Boltzman proposes: $S=k \, \ln W$ Meaning high entropy states can be realized via many different configurations. Truly ordered state (assume you arrange a sculpture from atoms) can be realized via much smaller number of microscopic states. So again, equilibrium is not order - it is a mess.


-2

Terms are conventions. With a point of view from the humans we are the order. Collecting something and order it in shells is order. But I agree with you that to order something needs energy and this led to misorder and this could be a possible convention too. But it is not.


1

Any finite physical system can be simulated by a universal computer. This includes quantum systems, which could be simulated by a universal quantum computer if we knew how to build one. Quantum mechanics is deterministic in the sense that the state of the whole of physical reality at one time can be worked out from the state at an earlier time given the ...


1

Could the universe be accurately simulated with an infinitely powerful computer? First Could and infinitely powerful are not compatible. A system able to simulate / predict accurately anything is quite impossible : one would need a clone universe able to compute faster than the universe runs. Initial values, indistinguishability and uncertainty ...


1

The uncertainty principle is often confused with the observer effect. The former says that the certainty in position times the certainty in the momentum is greater than some constant. We think of momentum and position as two different things, but the underlying physical phenomenon may not be. Of course, none of this speaks to whether or not quantum ...


3

Your question actually contains many questions, which are all related but not so strictly so that it is possible to give a full answer to it. Is every event in the universe related to each other? There are various ways to answer this question. Straight forwardly, we have observed that there is a finite speed at which information can propagate in our ...


0

By event I assume you mean interaction. There is certainly a randomness factor if our current theory of quantum mechanics is correct. The most obvious example is radio-active decay, but most any quantum mechanical interaction will include elements of randomness. As for the question of relatedness of events, the answer depends on what you mean by ...


2

The answer to the title question (Is every event in the universe related to each other?) is clearly a no. Some events can't be related to others due to the fact that light has a finite and unsurpassable speed.



Top 50 recent answers are included