# Tag Info

38

We don't know in general but to the extent we can measure, the laws seem to be the same, even if conditions are not. For example radioactive decay: We know how fast various elements decay, and we can observe the results of radioactive decay in distant supernovae. The conclusion is that, for at least some elements, the rate of radioactive decay is the same ...

22

The easiest explanation for why the maximum distance one can see is not simply the product of the speed of light with the age of the universe is because the universe is non-static. Different things (i.e. matter vs. dark energy) have different effects on the coordinates of the universe, and their influence can change with time. A good starting point in ...

21

If there is a way to violate a law of nature, it will become a law of nature as soon as it is discovered, studied and formalized into a scientific theory. Therefore, many new discoveries in science do violate (then current) laws of nature, but will not do so for very long. Often there are all sorts of medals and prizes involved too.

17

What you could think at first, regarding the orientation of any planetary system, is that it should be roughly in the plane of the galaxy, simply by angular momentum conservation. But, when you take a look at observations, you see that protoplanetary disks orientation is not what you would expect, with no preferential orientation (protoplanetary disks are ...

16

The total entropy actually increases, as the molecular cloud shrinks under gravity. It may seem that as the molecules are getting closer, they are more ordered, which means less entropy. That is however only one part of the process. The second (important) part is: when the molecules are closer, they also have higher kinetic energy (since they descended into ...

16

The tilt of our solar system (or any star system) is determined by the net angular momentum of the gas cloud from which it formed. This might be a bit of a vague answer, but over time, the formation of stars and their respective planets is thought to look something like this: Other influences (net forces: maybe nearby massive objects, or other components of ...

15

Hydrodynamic models of the Sun allow one method of estimating its internal properties. To do this, the Mass, radius, surface temperature, and total luminosity (radiative energy emitted)/s of the Sun must be known (determined observationally). Making several assumptions, e.g., that the Sun behaves as a fluid and that local thermodynamic equilibrium applies, ...

14

Do you mean, "Can we in principle", or just, "Can we..." ? The answer to the latter is no. We have no technology to create black holes. It was a remote possibility that was considered when creating the high energy densities in the LHC, but in practice the energies aren't high enough. Can we in principle do it? The answer is yes. If you can squash enough ...

14

Universality of physics As far as we know, laws of physics seem invariant both across space and time. It's not absolutely certain and taken for granted, there's lots of research probing to try and verify if perhaps something is slightly different far away or long ago, but to our best current knowledge the laws of physics work exactly the same in all faraway ...

12

In short: things can not move faster that light by theirselves, but they can move faster than light due to universal expansion. The more far away, the faster they go away.

8

The full equation for the time for an object to drop is $$t = \frac{ \arccos \Big( \sqrt{ \frac{x}{r} }\Big) + \sqrt{ \frac{x}{r} \ ( 1 - \frac{x}{r} ) } }{ \sqrt{ 2 \mu } } \, r^{3/2},$$ where $x$ is the radius of the sun, $r$ is distance of the object, and $\mu=GM=1.327\times10^{20}$. (in SI units, so you will need to convert your distance to metres, ...

8

The only limitations would be related to building an instrument large enough. There's a limit to the size of the finest detail a telescope can see. "Size" here is angular size, the angle that the detail is covering in the visual field. For a given wavelength of light, the smallest angular size depends on the aperture (diameter) of the telescope in a linear ...

7

This is a bit of a gray area, as an atmosphere doesn't have a clear boundary. That being said, Olympus Mons on Mars is so tall, the atmospheric pressure on top of it is only 12% the average pressure on the surface of Mars. That's near vacuum by terrestrial standards. https://en.wikipedia.org/wiki/Olympus_Mons#Description In general, for this to happen you ...

7

No. That's because we believe the laws of physics to be the same everywhere (this itself is a consequence of the law of conservation of momentum, via Noether's theorem). Therefore, if you can't violate the laws of physics as we know them on Earth, you can't violate them elsewhere, too.

6

The composition can be determined by taking spectra. Additionally, the mass can be determined through dynamics. If you combine these two, under the assumption that the star is in a state of hydrostatic equilibrium (which means that the outward thermal pressure of the star due to fusion of hydrogen into helium is in balance with the inward tug of gravity), ...

6

This question has two parts: Surface Temperatures A very useful diagram which shows surface temperatures, and also gives you the temperature of any star you can observe is the Herzsprung-Russell Diagram, this one from le.ac.uk. As you can see, the yellow of our own sun places it in the 4.5 kKelvin to 6 kKelvin, as noted in the question. This temperature ...

6

If you try to consider some hypothetical state of all particles, that state is almost certainly entangled. However, that does not mean that you can't (say) treat two particles at random as very probably independent of each other--effectively unentangled. The standard definition of an entangled state is a state that is not fully separable, i.e. one that is ...

6

By far the most particles in the visible universe aren't quantum entangled. That's obvious from observation, since if all electron spins e.g. would be entangled, all electrons would flip their spin at the same time, and we couldn't observe varying statistics of electron spins in a sample, resulting in varying degrees of magnetism, e.g. by applying gradually ...

5

I was just thinking about that and here is my layman's explanation. Imagine you're tracing two dots on a crumpled piece of paper, the dots are moving, but as they are moving, so is the paper getting ‘uncrumpled’, the actual distance between the dots will be more than the sum of distances they have travelled.

5

It is not a perpetual motion machine. Energy is being converted from gravitational potential energy in the gas, to motion, and eventually to heat which is lost as heat radiation. As this happens the planet shrinks and cools. This takes a long time, a lot longer than the few billion years of the the solar system. But ultimately convection will stop. All life ...

5

From one perspective, the purpose of a telescope lens, or mirror is to delay the light arriving in the centre of the instrument a bit relative to the light arriving at the edges. A lens is thicker in the middle, and light travels more slowly in glass, the path to the centre of the mirror and back to the detector is longer, because of the curve of the mirror ...

5

See also: Do the laws of physics work everywhere in the universe? Noether's theorem, in the context of this question, states that: If the laws of physics do not vary with position, then linear momentum is conserved (and vice versa). Therefore if we observe conservation of momentum (which we do with exquisite precision) then we do not expect the laws of ...

4

It would look very similar, but tiny differences are suspected, see e.g. this LHC experiment. Here a list of more antimatter experiments at CERN. See also CP violation on Wikipedia hinting towards tiny differences between matter and antimatter. Immediate consequence: The CP violation parameter of the CKM matrix in this Wikipedia article would be different,...

4

This comes from a misunderstanding of local and absolute. There is nothing to prevent a local increase in order - overall, order still decreases (or in common terminology, entropy increases) From Wikipedia: According to the second law of thermodynamics the entropy of an isolated system never decreases, because isolated systems spontaneously evolve ...

4

Kind of a quick answer, if you don't mind. Can we compress any object to create black Holes? The pressure at the bottom of the ocean is enormous, it would kill a person in a fraction of a second, but it's tiny compared to the pressure in the center of the earth, and that's tiny compared to the pressure in the center of Jupiter, and that's tiny compared ...

3

No. That's not what a black hole is. A black hole is a vacuum solution to general relativity. In other words a black hole is just mass, without a "thing" left to be massive. The mass is collapsed to a singularity, and is surrounded by an event horizon. If you pass over the event horizon, every path you can take in will lead you to the singularity. In this ...

3

I love Ned Wright's cosmology tutorial and I highly recommend it, but that statement by him is at the least very misleading. Superluminal recession speeds plainly can't be related to spacetime curvature because they don't vanish in the limit of zero curvature (zero energy density or zero $G$). The real reason that distances can be larger than $c$ times the ...

3

The completely unscientific explanation... Imagine the universe to be a balloon. Two bodies start close to each other but on opposite surfaces. The expansion of the balloon takes them away from each other at equal speed and such a rate that the light from one at its starting point takes almost the entire history of the universe to reach the other. The ...

3

Thermonuclear fusion has nothing to do with the central temperature of the Sun. You can get a rough estimate of the temperature (with some necessary simplification) following this line of reasoning: The material of the Sun is an ideal, completely ionized, gas (all electrons are separated from nuclei); This means that pressure of the gas is proportional to ...

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