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Janus

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Janus last won the day on May 11

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  1. While we don't know it to 100% absolute certainty, ( experiments have only been able to set an upper limit for photon mass), It is consistent with our understanding of the universe. Relativity, which has passed every test thrown at it so far, Says that anything that has zero rest mass must travel at c and only c (in a vacuum). If something has even the slightest bit of rest mass, it can travel at any speed from 0 up to, but not including, c. So, if a photon had any rest mass at all, we should be able to find at least some photons traveling at speeds well below c. So far this has not been the case. So both theory and observation seem to indicate that photons are indeed massless, and unless something crops up to cast doubt on this, it's the way to bet.
  2. That timer on the screen is just showing the time according to the frame of the camera that recorded the image, and there is nothing unique or special about that choice of frame. You could have also had cameras attached to the individual players, each with its own timer. The recordings made by these cameras would be just as valid as the stadium camera. While the stadium recording might show that two events at different ends of the field occurred at the same moment, a player camera may show that they did not. And there is no reason t accept the stadium camera's determination over that of the player's camera. So the fact that anyone watching the recording sees the same events occurring at the same time mark of the digital time stamp, just means that they all agree that this was what was recorded from the reference frame of the camera, not that this represents any kind of universal absolute time.
  3. It is not just that the train observer "sees" the lightning strikes at different times, for him, the strikes occurred at different times. So for the embankment observer, the strikes actually hit the front and back train simultaneously, while for anyone riding in the train, they they do not strike the ends of the train simultaneously. What Einstein is saying is the the very notion of "simultaneous" is frame dependent and is not absolute.
  4. Just to expand a bit on my last post: If you look at this diagram, you can see how to orient Mercury's orbit. https://en.wikipedia.org/wiki/Longitude_of_the_periapsis#/media/File:Orbit1.svg For Mercury, the reference direction is the vernal equinox. It is a point on the celestial equator, just a bit South of Pegasus. For this line, you would measure the longitude of the ascending node. For the epoch starting on J2000 ( astronomy uses Julian years), for Mercury, this is 48.33076593 degrees. Using this as a reference, you tilt the the orbit by the inclination ( 7.000497902 degrees). Then you measure out the longitude of periapsis ( longitude of perihelion for Mercury: 77.45779628 degrees) A line passing through this point and the Sun follows the line of apsides ( which passes through both foci). Now, as already mentioned, the values given are not constant. So for any given date, you will have to take into account that the inclination changes by -0.00594749 deg/century, the longitude of the ascending node by -0.12534081 deg/cen, and the longitude of perihelion by 0.16047689 deg/cen. And even these values are only good for the interval of 1800 AD-2050 AD
  5. Orbital velocity can be expressed as the tangential velocity for a circular orbit. The magnitude of the escape velocity is independent of direction. (technically it is escape speed). An escape velocity trajectory will follow a parabola. So, if you are already in an orbit, it is most efficient to achieve escape velocity by boosting your speed in the direction of your current orbital velocity. In fact, the equations for circular orbital velocity and escape velocity only differ from each other by a numerical factor.
  6. I think you've succumbed to a common misconception about gravitational waves ( the term "gravity wave" actually refers to something like ocean waves, which are affected by gravity) Gravitational waves are not the source of, nor the means by which the "force" of gravity is mediated. Gravity is a field. Gravitational waves just carry information about changes in the field. The gravitational attraction between masses would exist even in a situation where no gravitational waves were present.
  7. There are a number of elements that are used to fully describe a planet's orbit.: The semi-major axis of the orbit (average orbital radius) The eccentricity ( how elliptical the orbit is) The orbital inclination The longitude of perihelion The longitude of the ascending node. The last three are measured with respect to the Earth's orbit around the Sun. The imaginary plane which passes through the Earth's orbit is the ecliptic. The orbital inclination is how much the planet's orbit is tilted relative to this plane.* The longitude of perihelion is measured relative to the Vernal equinox. (draw a line from the Sun that passes through the Earth's orbit where the Earth would be on the date of the spring equinox.) If you draw a line between planet and Sun when the planet is at perihelion ( the closest point of its orbit around the Sun, the angle between this line and the line above will give you the longitude of perhelion. (which also gives you how the major axis of the orbit is aligned). The longitude of the ascending node gives you where the plane of the planet's orbit and the ecliptic cross each other. *Because the Earth is subject to various gravitational disturbance from other planets, this plane can change. To keep things simple, the ecliptic is defined as the plane of the Earth orbit on the starting date of the epoch we are presently in. That way, we aren't always adjusting the inclinations of the other orbits due to the Earth own orbital changes.) All of these elements are subject to change over time due to being perturbed by other bodies in the solar system. The Horizons web site can give the these values and the position of a planet for any date: https://ssd.jpl.nasa.gov/horizons.cgi#top
  8. For long distances, there is a hypothetical means of travel known as the "gravity train". Basic concept is this: You start by digging a tunnel with a downward slope. You keep digging in a straight line. Since the Earth's surface is curved, your straight line tunnel will end up coming out at some other point of the Earth's surface. The midpoint of the tunnel will be closer to the center of the Earth and thus lower than the ends. You seal and evacuate the tunnel of air and put a mag-lev train in it. If you start the train at on end, it will slide down the tunnel picking up speed until it reaches the mid point, and then will climb back up the other side, coming to a stop at the other end. Now here's the kicker: No matter how far apart the ends of the tunnel are from each other, the trip will take a bit over 42 min. Of course, you would never be able to eliminate all friction and losses, so you would have to add a bit of energy to get the train to reach all the way to the other end. Also, the further apart the ends, the deeper the depth of the midpoint, so there would be practical limits on just how long you could make the tunnel. It's a neat idea, even if it never becomes practical.
  9. In the equation, r is measured from the center of the Earth. It seems that you just plugged 424 in for r. The answer you got would have been the GPE for the spaceship if it were sitting on the surface of a world with the mass of the Earth, and just 424 m in radius. For one, you have to convert km to meters, and for the other, you are looking for the difference in GPE between sitting at the surface of the Earth and being 424 km above it, not just the GPE for some point.
  10. Janus

    Pangaea ?

    Pangaea is just the last of a series of super-continents that existed in the past. The land masses had collided and separated in ages prior to its formation. As far as an imbalance is concerned; The entire mass of the Earth's crust is 2.77e22 kg, which is just 1/72 the mass of the Earth. In addition, continental crust is actually less dense than oceanic crust. So while the crust is thicker under the continents, it doesn't weigh that much different per square mile than oceanic crust. Thirdly, even if there were a slight shift in the mass of the Earth, it wouldn't cause an " imbalance". The axis of rotation would just shift to pass through the new center of mass. It isn't like a washing machine drum which starts to shake the whole machine if the load is unbalanced. In this situation, the axis of rotation is fixed relative to the washing machine and can't shift in response to the center of mass change. Thus the whole washing machine moves in response. The Earth rotates freely in space and is not connected to something else like the drum is connected to the washing machine.
  11. Janus

    Voting By Mail

    Someone might Have already answered this later in the thread ( I did a quick perusal, but might have missed it.) Isn't wasn't about the Democratic primary. There was also a State Supreme Court position up for election. The seated judge was a Trump-supported conservative, and the opponent was more liberal. By forcing the vote, and reducing the number of polling places in Democratic leaning Milwaukee to 5, the hope was to keep voting down (which generally favors Republicans anyway), especially in places that generally would vote Democratic. As it turned out, it didn't work, or at least not well enough, as the Trump-supported seated judge lost to his opponent.
  12. Janus

    Gravity

    We have already detected gravitational waves. However, neither gravitational or magnetic attraction is mediated by waves. A "magnetic wave", is just one component of an electromagnetic wave, or in other words, light and radio waves. Magnetism, as in the attraction and repulsion of magnets, is due to a field, not a wave.
  13. A computer game built for a Commodore 64 isn't going to be accurate in terms of actually flying a real helicopter . If it were, it would just be frustrating for anyone trying to play the game. They'd start playing the game, crash, try again, crash,... Most people would just eventually give up. Besides, a Commodore 64 wouldn't even be up to producing a realistic flight model to begin with. There are some more realistic simulators out there, Microsoft made one that included helicopters. But even then, you can change the settings in terms of how realistic the flight model is. To go from no experience to being at all proficient, you would start at the lowest realism settings and ramp up the realism ( such as correcting for air turbulence) as you become more comfortable.
  14. The claim that element 115 fuel UFO's comes from before element 115 was ever actually synthesized. At that time, they would claim that it had all sorts of bizarre properties that made it suitable for that purpose, based on the fact that none existed to prove them wrong. I also remember a claim that UFO flew by manipulating gravity. But they claimed that it was by controlling Gravitational waves*. I can only assume that they had read that there was a such a thing, and thus assumed that they were what were responsible for gravitational attraction. Therefore, if you could control them, you could control gravity forces. As this is complete bollix, (gravitational waves are not what are responsible for gravity.), Their "explanation" wasn't worth spit. * Though if I remember right, they use the incorrect term "gravity waves".
  15. If you mean "dead" star rather than "deadly" star, You'd still be wrong. Stars all, at some time or another, had hydrogen fusion occurring in their cores. This is not the case for or any of the other planets in our solar system. They instead are classed as sub-stellar objects.
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