Energy is what is called a scalar in physics. A scalar is a measurement that has a magnitude, but not a direction. Distance and time are other examples of a scalar. Vectors are measurements that have both magnitude and direction. Acceleration, force, and velocity are all examples of vectors.
Note: velocity and speed are not interchangeable in physics. Speed is a scalar, velocity is a vector.
Why is this important to know that energy is a scalar? Scalars are generally always zero or positive. So typically, the energy of a system is always zero or greater. The concept behind negative energy is this:
Suppose you have two objects separated by an infinite distance. The sum total of their energies is zero. Gravitational force then accelerates the two objects together. Therefore, the energy the system is increasing. But a closed system cannot change its energy. Therefore, the difference between the initial condition and the final condition is negative, hence negative energy.
Negative energy is a strange concept to understand and it's only theoretical since the above situation is very simplistic. However, if it does exist and we can harness it, negative energy can lead to humanity colonizing the galaxy (well, at least the local neighborhood). Negative energy can impact warp drives and may be used to stabilize wormholes.
Showing posts with label gravity. Show all posts
Showing posts with label gravity. Show all posts
28 June 2016
26 May 2015
Planetary Alignment
Every once in a while, a story comes out that a planetary alignment will wreak havoc on Earth and the end of the world as we know it will occur. The most recent example was posted by a friend of mine on Facebook. It basically tells us that a planetary alignment will cause a massive 9.8 earthquake in California on May the 28th. Here is a link for the story if you wish to read it. I admit that I didn't read it because I have one thought on stories like this: they basically come from the back end of a male cow.
These stories are bogus. They are a waste of electrons on the internet. People that don't know science are taken in by these articles because of the gloom and doom that they predict. I'm going to explain why these stories are false.
1. The Sun is the overwhelming largest mass in the Solar System, and by a large margin, contributes the largest component of the force of gravity on the Earth. All the other planets, moons, asteroids, comets, minor bodies, dust particles, alien lifeforms, nanobots, whatever, in our Solar System combined do not contribute much to the force of gravity felt on Earth. Remember, the force of gravity is related to the mass divided by the distance squared (higher the mass, higher the gravity; closer the mass, the higher the gravity as well). Remember, that the Sun contains over 99% of all the mass in the Solar System, and that there are only six objects in Solar System closer to Earth than the Sun (Mercury, Venus, the Moon, Mars, Phobos, and Deimos). They do not have enough mass combined to do anything to our planet. In fact, the only other mass that has an significant affect on Earth is the Moon, and all it does is make water slosh around (see the post on tides).
2. The planets themselves cannot align themselves in such a way that they all are pulling on Earth in the same direction, even if the gravity was strong enough. All the planets are inclined differently to the Sun's equator, and in turn, to the Earth's orbital plane. One planet might be above the Earth's orbital plane, while another below it. Note that it is possible that the planets might all be in the same orbital plane as the Earth as they orbit the Sun, but this is highly unlikely due to all the motions of the planets. But again, it is extremely unlikely that they all would happen to be in the same orbital plane as the Earth, and even then, look at the first point.
I am betting that if you read my blog, you know that these stories are blatantly wrong. However, if by some chance you believe them, just understand, planetary alignments will not hurt the Earth in anyway. I'd be more worried about the people living on the planet.
These stories are bogus. They are a waste of electrons on the internet. People that don't know science are taken in by these articles because of the gloom and doom that they predict. I'm going to explain why these stories are false.
1. The Sun is the overwhelming largest mass in the Solar System, and by a large margin, contributes the largest component of the force of gravity on the Earth. All the other planets, moons, asteroids, comets, minor bodies, dust particles, alien lifeforms, nanobots, whatever, in our Solar System combined do not contribute much to the force of gravity felt on Earth. Remember, the force of gravity is related to the mass divided by the distance squared (higher the mass, higher the gravity; closer the mass, the higher the gravity as well). Remember, that the Sun contains over 99% of all the mass in the Solar System, and that there are only six objects in Solar System closer to Earth than the Sun (Mercury, Venus, the Moon, Mars, Phobos, and Deimos). They do not have enough mass combined to do anything to our planet. In fact, the only other mass that has an significant affect on Earth is the Moon, and all it does is make water slosh around (see the post on tides).
2. The planets themselves cannot align themselves in such a way that they all are pulling on Earth in the same direction, even if the gravity was strong enough. All the planets are inclined differently to the Sun's equator, and in turn, to the Earth's orbital plane. One planet might be above the Earth's orbital plane, while another below it. Note that it is possible that the planets might all be in the same orbital plane as the Earth as they orbit the Sun, but this is highly unlikely due to all the motions of the planets. But again, it is extremely unlikely that they all would happen to be in the same orbital plane as the Earth, and even then, look at the first point.
I am betting that if you read my blog, you know that these stories are blatantly wrong. However, if by some chance you believe them, just understand, planetary alignments will not hurt the Earth in anyway. I'd be more worried about the people living on the planet.
04 February 2015
General Relativity and Astronomy
Previously, we discussed how mass can curve space(time) due to general relativity. Why is this important?
The curvature of mass leads to interesting phenomena. The first is it causes the perihelion of a planet orbiting the Sun to precess. Secondly, it causes light actually to bend - yes, gravity affects light - and this leads to really weird stuff.
Let's look at the first one. The best example of the precession of a planet at it orbits the Sun is the path of Mercury. This was discussed back in the post about Mercury and General Relativity. The highlight of the discussion was that as Mercury orbits around the Sun, at perihelion, Mercury is in the deepest part of the gravity well created by the Sun. As it continues to orbit, each successive perihelion moves farther ahead in its orbit. The perihelion of Mercury was noticed in the mid 1800s, but was thought to be caused by an inner planet. But after Einstein's Theory of General Relativity was developed, the equations were able to show why Mercury's orbit precessed around the Sun. Everything that orbits around another body shows this precession, with the amount of precession dependent on the mass of the central body.
The second one seems a little weirder. From Newton's equation for universal gravitation, we see that the force of gravity is dependent on mass. However, light and all electromagnetic radiation are massless. So how does gravity bend light?
In a nutshell - gravity wells.
If a star were behind the Sun, in Newtonian gravity, we would not be able to see it, because gravity only affects objects with mass. We would see something like this.
However, because of General Relativity, light will bend in the presence of a gravitational field. The light from the star will curve around the Sun and we can see it from Earth.
This was actually proven by Sir Arthur Eddington. In 1919, there was a solar eclipse that he observed and photographed. When the pictures were analyzed, they could see the effect of gravity on stars. This analysis only worked during an eclipse because otherwise, the Sun would be too bright and wash out the background stars. Eddington gave physical proof that General Relativity was correct!
Positive and Negative Image of Solar
Eclipse of May 1919
Image Credit:
This phenomena of light bending around masses also is used to search for exoplanets. As a planet passes in front of star, that planet can bend the light towards us. This process is called lensing. Not only does it allow the light to reach us even if the source is behind the mass, it can also magnify the light, making it brighter. Most of the gravitational lensing seen are galactic in nature.
The curved arcs are the lensed
(background) object. The centers are the lenses bending the light.
Image Credit:
Einstein's Cross (Gravitation
Lensing) - Quasar being lensed by a central dim galaxy
Image Credit:
Einstein Ring - When the background
object is perfectly aligned with lensing object and the Earth, a complete ring
can be created
Image Credit:
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