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General and Special Relativity
Relativity is the theory stating that all measurements depend on the relative motions of the observer and the observed. The theories of general and specific relativity were both proposed by Albert Einstein.
813 Questions
Oh, dude, the SI derived unit is like the cool kid in the metric system gang. It's basically a unit that's made by combining base units, like meters and seconds, to measure stuff in a fancy, standardized way. So yeah, it's like the VIP of units, but no need to stress about it, man.
What would happen if the speed of light was infinite?
technically the speed of light is not infinite. but passing the speed of light means
that you would travel backwards in time. so if the speed of light is infinite, then
the years that passed will get brighter and brighter. So ancient times would be
burned to crisp while the future would be dim. the concept here is that light dims
as the farther you travel forward in time. that is because all the light is past the
spped of light so they travel backwards in time.
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Thinking in terms of a few things that are the way they are today because of the
finite speed of light, this becomes a fascinating question to ponder. For almost all
of human history, until only the most recent few moments, it made no difference.
But I can think of a few modern cases where it does:
-- Radio communication.
Radio, TV, cellular, GPS etc. all become much more reliable, as 'multipath' fading
ceases to exist. Multipath fading is attenuation arising from the phase difference
between the direct and the reflected signal, due to the difference in transit time
over paths of different lengths. With infinite propagation speed, there is no delay
over a longer path, so no phase difference at the receiver. All rays add !
-- Stars no longer 'twinkle'.
Scintillation of an optical point source is exactly the same multipath fading from
the radio world.
-- Laser holography . . . not possible.
-- Directional antennas ... Yagis, ham beams, log periodics, AM tower arrays, any
'parasitic'
structure ... are no longer directional. But I think parabolic reflectors still work.
-- Fermat's Principle ... which I no longer understand ... involving, as it does, the speed
of light, is out the window. The laws of reflection and refraction don't depend on Fermat,
but they can be derived from it. Since it no longer holds, you don't suppose . . .
-- Young's experiment, coherence, interference from thin films, Michelson's interferometer,
diffraction, Bragg's Law . . . all gone.
-- GPS can't exist ! At least not the way it operates now. The device in your hand
or in your car compares the different lengths of time it takes for the GPS signals to
reach you over the different distances from several satellites in different places. If
the speed of light (and radio) is infinite, then it makes no difference where you are
or where the satellites are. It takes no time for any signal to reach you from any bird.
-- And if the speed of light is infinite in all media ! ! . . . no refraction. Goodby to Snell,
lenses don't work, spearing fish is no problem as long as you're not severely myopic, and
the pencil still looks straight when half of it is under water.
-- Woo hoo ! You MUST be myopic ! Just like everybody else in the world. MAYBE
you can form a workable visual image of an object at infinity, by stopping your pupils
down to pinholes, I don't know. But for nearby objects, forget it ! The cornea, the lens,
the humors, nothing can help your focus.
-- Driving: Police radar still detects your car, but I think the Doppler shift is gone,
so your speed can't be measured with it.
-- Same for Doppler weather radar. It has no advantage over older radar. It tells you
that a thunderstorm cell is right there, but it can't tell you anything about winds or
rotation inside the cell.
-- Oops. Sorry. Radar doesn't work too well at all. It can still tell you the direction
to the target, because that's the direction where you send a burst and some of it
comes back. But it can't tell you the distance to the target, because the echo
returns from a near target or a far target at the same time.
In fact, maybe the whole echo-detection scheme can't actually be implemented in
hardware, because echoes return in zero time, before you've ever had a chance to
turn off your burst transmitter and listen for the echo.
-- Which brings us to Astronomy and Cosmology: We can see the status of every
object in the universe that's bright enough for us to detect, right now. We can't
see the evolution or distribution of galaxies in the early universe ... no "looking
backward in time". No red shift, no blue shift, so we can't detect radial speeds,
and we lose most or all of the overwhelming body of data that's explained now by
the concept of the "expansion" of the universe.
-- Relativistic effects: As mind-bending as this is under 'normal' circumstances, it's
more so if we imagine a fundamental change in the nature of light.
. . . We know right away that speed no longer affects mass, and that the Lorentz contraction
and time dilation both go away, because no matter how fast you move, v2/c2 is always zero.
. . . It becomes a lot easier now to accelerate your car or your spaceship all the way
to 3 x 108 meters per second, but now, that's still 0% of the speed of light !
. . . Photons can now have rest-mass if they want it. And if they don't then their mass
is still zero when they're whizzing about.
. . . But then, how can photons carry energy ?
. . . Does that mean that E = mc2 goes away ? Well phoo, I guess it had to anyway,
as soon as 'c' became infinite.
Those are the first few minor consequences of infinite light speed that I can think of just now.
How can the speed of light be constant and relative at the same time?
No, any measure of the speed of light will be the same regardless of the frame of reference. The constancy of the speed of light is allowed for by time dilation. Because you are in motion toward the source, your clock runs slower than an identical clock in a rest frame, so your measure of the speed of light remains constant because time is flexible. However, the Dopper effect will cause the light from the source you are approaching to seem to increase in energy (frequency), so will be blue-shifted.
How far away is the event horizon of Sagittarius A from it's centre?
The mass of the black hole in Sgr A* is estimated at approximately 4 million solar masses (see related links).
Assuming its rate of rotation is sufficiently small, we can estimate its Schwarzschild radius R, i.e. the radius of the event horizon, using the following formula from General Relativity:
R = 2GM / c2
where G is the gravitational constant and c is the speed of light. M is simply the mass mentioned above.
This gives a radius of approximately R = 1010 m, which is very roughly a tenth of the distance between the Earth and the Sun.
Why do you not normally notice a blind spot when you look at your surrounding?
Our brains "fill in" what it presumes is there. That's why some optical illusions can trick your brain into "seeing" what is not there -- the brain makes a reasonable guess, but it guesses wrong.
How hot and cold temperature affect air balloon?
Hot temperatures can cause the air inside the balloon to expand, making the balloon rise. Cold temperatures can cause the air inside the balloon to contract, making the balloon descend. Changes in temperature can also affect the buoyancy and stability of the balloon during flight.
Can perpetual motion be achieved using a pendulum in a vacuum?
Yes. In a vacuum, the only resistance is the friction in the suspension for the bob of the pendulum. Other than that, it should swing a long time. In air, friction with air will add to the friction in the suspension and it won't swing as well as it would in a vacuum. But it will swing for a while. A pendulum will swing in water, but the hydrodynamic drag will make it stop in a really, really short period of time. Just a couple of swings will strip the pendulum of almost all its energy. And the speed of the pendulum will be slower than in air, and it won't swing anywhere nearly as far through the bottom of its arc as it did in air.
Why does it take more energy to go faster?
"Kinetic energy" is energy of motion. When you, or any object, move faster, you
have more kinetic energy. In order for you or any object to speed up, it needs to
have more kinetic energy, and that energy has to come from somewhere. It can
come from gasoline burning in the engine to turn the wheels faster, rocket fuel
burning in the combustion chamber to accelerate the spacecraft, RF current
through the magnets to drag the protons around the ring faster, or glucose
burning in the muscles to make the legs go faster. But if more speed is needed,
then it'll take more kinetic energy, and that energy must come from somewhere.
Time and space are interconnected according to the theory of relativity. Time can affect space by bending it, creating what we know as gravitational effects. The presence of mass or energy can bend and warp spacetime, influencing the motion of objects within it.
What causes a column of air spinning like a roll of toilet paper to turn into a vertical position?
If you are referring to the formation of a mesocyclone, this occurs when the horizontal vorticity meets the updraft. The updraft helps lift the vorticity upwards and in the process tilts the axis from horizontal to vertical.
Who developed the theories of special and general relativity?
Albert Einstein developed the theories of special and general relativity. Special relativity, published in 1905, deals with the relationship between space and time. General relativity, published in 1915, extends these ideas to include gravity and the curvature of spacetime.
What can be said about beggning of time?
When we say about the beginning of time we basically are talking about point Zero, the beginning of everything, the beginning of the universe. When did time begin? It is 13.7 million years ago, which is approx.
The magnitude of the effort is controlled by you, not by the distance of the load
from the fulcrum.
Moving the load farther away from the fulcrum has no effect on the effort. But if
you want to leave the effort where it is and still lift the load with the lever, then
you're going to have to increase the effort.
Do points in time and space exit?
This is in interesting question, one that I think has more in common with philosophy than science, but I can give my view on the subject.
I generally ascribe the an instrumentalists perspective, meaning that I consider agreement with experiments the sole measure by which scientific theories should be judged. This is in contrast with other people who say a scientific theory should also explain why things are happening.
Why do I mention this? Well because I view points in space and time to be part of the mathematical construct that we use to describe the Universe, and that they are not necessarily real entities. We can certainly not go out and touch random points!
How the invariance of the speed of light leads to time dilation and mass enhancement?
For two differently moving frames of reference to measure the same speed of light as required by standard Maxwell electrodynamics, time and the length of objects must change to accommodate for the difference they should see by traveling at different speeds/directions. The extra mass comes from the fact that nothing can reach the speed of light, and so if y
Which type of connection is used for home wiring?
Every single outlet and light socket in your house is in parallel with every other
one, and also with all the outlets and sockets in the homes of several of your
neighbors . . . all of the houses served by the same pole transformer.
How electricity is produced in Antarctica?
No, if you what you mean "is electricity transmitted from Antarctica to other continents?" There are several scientific research outposts in Antarctica, all of which make their own electricity using generators run by diesel engines. Of course, the diesel fuel is imported. The transportation factor makes this some of the most expensive electricity in the world.
Your writer spent the year 1963 at South Pole Station doing auroral research and remembers very well when our generators stopped because ice had plugged the fuel lines. We were grateful when our technicians fixed the problem after several hours of our being in the dark and cold.
Which material melts ice most efficiently?
Calcium Chloride, CaCl2 or pure calcium. It makes the best exothermic reation which melts the ice better. Salt is actually a poor ice melt when compared to others and it's bad for the environment, yet it is still widely used because it is so inexpensive.
Is the total angular velocity of the universe zero?
Hmm...angular velocity. First of all, when you talk about the universe, it seems like you are talking about an object. But the universe is a rapidly expanding object of space and time, so there should be no real boundaries. That means it can't really rotate at all. So, in conclusion, using angular velocity is not suitable for measuring what you are trying to find.
Quel temps fait-il en octobre en Australie?
En octobre, c'est le début du printemps en Australie. Les températures commencent à se réchauffer, avec des moyennes généralement comprises entre 15°C et 25°C. Les précipitations peuvent varier en fonction des régions, mais le temps est généralement agréable.
How can warp drive be achieved?
At the present state of the art in Physics and Engineering technology, the only known means of achieving
warp drive is by watching a lot of old episodes of Star Trek ... enough to make you believe you're aboard the
Enterprise, happily drifting through the cosmos in a glorified tin can along with Dr. Crusher and Marina Syrtis.
However, there are other technical possibilities such as the phase-shifted electrodynamic propulsion. See the related link.
An Alcubierre drive is a hypothetical engine which is capable of faster than light travel by enveloping the spacecraft in a bubble of curved spacetime. This shell is allowed to travel faster than light, the spacecraft moving less than the speed of light inside the shell.
The drive does require the existence of a type of exotic matter; matter with an imaginary mass. Such matter has never been observed and is considered highly speculative.
Why sun appears flattened at sunrise?
This is an optical illusion caused by the fact that the sun's rays are passing through the atmosphere at a low angle - hence they pass through a lot more atmosphere relative to when it is high in the sky.
The atmosphere of the earth not only being full of contaminants which tend to disperse the light (the same reason why you see the beam of a torch) but it also can refract and bend the rays due to it being a more dense medium than space.
Combined these have the effect of making the sun appear larger, often a darker hue, and the flattening you see when it rises/sets.
Can a projectile become a satellite given an appropriate initial velocity and position?
Yes, a projectile can become a satellite if it is given enough velocity to enter orbit around a celestial body. The projectile must be launched at a specific angle and velocity to achieve a stable orbit. If these conditions are met, the projectile will remain in orbit around the celestial body as a satellite.
