Senior Members
  • Content count

  • Joined

  • Last visited

  • Days Won


Janus last won the day on October 31

Janus had the most liked content!

Community Reputation

724 Glorious Leader

About Janus

  • Rank
  • Birthday August 28

Contact Methods

  • Website URL
  1. Braking using Escape Velocity

    An object moving at 0.01c while still very far from the Neutron star, will be accelerated by the star's gravity as it approaches, by the time is is 25,000 km from the star, it will be moving at ~0.0148c relative to the star ( nearly 50% faster than escape velocity for that distance). As it climbs back away from the star, it will lose that gained speed and once it gets back to being very far from the star is will again be moving at 0.01c with respect to the star. It's path will be deflected by some amount. Now you could use this deflection to alter the object's speed with respect to its target, but this would involve the Neutron star itself as having a significant velocity with respect to the target. You would being doing the reverse of what happens when we use a planet for a gravitational assist, where we transfer some the planet's momentum with respect to the Sun to the probe. This can also be used to go the other way, transferring momentum from probe to planet. In this case we would need to transfer momentum from our object to the neutron star. This will allow use to reduce the object's speed relative to some reference system, but only if the Neutron star has the proper velocity with respect to that reference frame.
  2. While a supernova would scatter elements into the galaxy, I doubt any of it would reach another galaxy. As far as heavy elements in the inner planets go, Earth has a density of 5.52 g/cm3, Venus 5.24 g/cm3, and Mercury 5.43 g.cm3 . Earth has the highest density, but is also the largest. This becomes a factor because as a rocky planet gets larger, the pressure at its interior increases, which compresses the core and brings up the average density of the planet. Earth's radius is 5.4% greater than Venus' and its density is 5.3% greater. Earth's Mass is 22.6% larger than Venus. We can assume that at least some of the average density difference is like due to the greater compression at the Earth's core due to its larger size. The Earth is only 1.7% denser than Mercury but its radius is 161.4% greater. Mercury is smaller than Mars, and has a density 38.2% larger. From this we can conclude that Mercury has a higher percentage of heavier elements than the Earth does. Exact values for the total elemental make up for Venus or Mercury don't exist. Only two landers have ever done a test of the crust of Venus, and this is not enough to tell us about the planet as a whole, And the only mission to Mercury was a fly-by.
  3. To give an good answer to your question, a few more details are needed. You say that the asteroid passes on a path that is parallel to the Earth's orbit. Did you mean that this was the direction of the path at the moment of closest approach, or was this the path the asteroid was following before being effected by the Earth's gravity. An object with the stated velocity and distance from the Earth at perigee, would have had its trajectory altered by almost 60 degrees from the time it started to be majorly effected by the Earth's gravity and the time it reached perigee. Given your numbers, I figure that the Earth's orbit would be altered by ~440 m/s. Exactly what effect that would have on the Earth's orbit depends on the trajectory of the asteroid. For example, if the trajectory is such that in passing over the Northern hemisphere, the plane of the Earth relative trajectory is at right angles to the ecliptic, then the majority of the change will be to the inclination of the Earth's orbit (~0.84 degrees), with just a small change to the Earth's orbital speed (~3 meter/sec), Again, here we are assuming the the asteroid's path at perigee is parallel to the Earth's orbital path. As far as tidal effects go, tidal force decreases by the cube of the distance, so, 16 times the mass at 1/2 the distance equals 128 times the tidal effect at perigee. Over the course of ~6 1/2 days, the tidal force from this body will increase from equal to that of the Moon to 128 times that of the Moon, and then decrease back to equal to the Moon in another 6 1/2 days.
  4. Dark Matter or Dark Force

    What is it that makes "matter"? We consider a table as being made of matter. I can touch it and it feels solid. But what is really happening I "touch" the table. My hand, and the table is made up of atoms with electrons in shells around a nucleus and these electrons have electric fields. So what is happening is that my the electric fields of the electrons of the outer layer of my hand interact with the electric fields of the outer layer electrons of the table. It is just an interaction of fields and nothing is really "touching" anything in the way we commonly think about it. The matter of the table is made of atom bound together by electromagnetic forces. Are the atoms themselves matter? We generally say that they are. Atoms are made up of electrons, protons and neutrons. Are they matter? Again, we tend to say that they are. Protons and neutrons going further are made from quarks. Quarks and electrons are considered fundamental particles, They are also considered matter particles. So, what are these fundamental particles made of? are they little balls of "something" that is imbued with the properties we measure the particle as having, or are they just the some total of the properties they exhibit? Thinking of them in the first way seems like trying to extend the analogy of how the macroscopic world appears to be down to where it doesn't hold. It seems much more likely that the second view is better, a fundamental particle is just "made up" of its combined properties. It has a mass and maybe a charge, etc. and fields associated with them, and the only way to interact with them is through these properties. They are just entities with a collection of properties. If this is the case, Is there a single property that defines its "matterness". If it can't interact through the electromagnetic force, is it not matter? Is the Neutrino matter? it has mass, but no charge, it also interacts with other matter rarely and only under certain conditions. A neutrino could pass through light years of lead without having one interaction. Would you call a neutrino "matterless mass". The WIMP model for dark matter just assumes that is is made up of particles like the neutrino, and which share like properties in some respects.
  5. Dark Matter or Dark Force

    The distribution of dark matter does match what you would expect given its properties. It does interact by gravity( both ways), but not by electromagnetic interaction. It is this difference that results in DM being spread out in a sphere while visible matter tends to collect into a more compact shape. It means that dark matter can't 'collide' with visible matter or other dark matter. Dark matter just passes through everything, including other dark matter. When visible matter collides ( or even makes a close approach) it interacts electromagnetically. It can either be deflected or the colliding matter could stick together. In either case, there is an acceleration which causes the matter to emit electromagnetic waves which come at the expense of kinetic energy, Colliding matter will give off heat and the resulting combined mass will have less momentum than it started with. If there is a deflection, the individual components will separate at speeds lower than what they approached at. This lower speed means that they will be more likely to be drawn into further interaction. A large collection of visible matter will, through al these energy shedding interactions will tend to collapse into a denser arrangement before it becomes relatively stable. When DM makes a close approach, it may have its trajectory changed by gravity, but this acceleration does not result in the production of EM radiation and thus no subsequent loss of energy. The participants of the encounter end up leaving with the same total momentum that they started with. Without this mechanism for shedding kinetic energy, a DM cloud has no tendency to condense into a denser structure.
  6. Dark Matter or Dark Force

    Because the solar system has a high concentration of visible matter in it even compared to the local galactic neighborhood. The local part of our galaxy has an average density of ~2e-9 kg/ km3. If we take the total mass of the solar system and average it out into a sphere with a radius equal to Neptune's orbit, its average density works out to being ~5 kg/km3. Much more tightly packed. The density of dark matter in the vicinity of the Solar system is ~6e-13 kg/km3. Much less dense than even even the average galactic neighborhood. ( it works out that the expected amount of dark matter within the confines of the solar system is equal to about the mass of a small asteroid. So if dark matter is so sparse, how can it have such a large effect on the galactic rotation curves?. It's not confined to the galactic disk like the vast majority of the visible matter is; it is spread out into a spherical halo in which the visible galaxy is embedded. To work out how much gravitational effect it would have on a star orbiting a galaxy, you would need to calculate the total mass of DM contained in a sphere with a radius equal to the stars distance from the center of the galaxy. With our own sun, some 26,400 ly out, and using the average density of DM in the local neighborhood, this work out to 2e10 solar masses, or a sizeable fraction of the galaxy's entire visible matter mass. (the real amount will actually be a bit more, since the dark matter density does increase a bit as you move towards the center of the galaxy.) So while there would not be not enough dark matter in the solar system to measurably effect the motion of the planets, it would still add up to be more than enough to effect the galaxy as a whole. Solar system = relatively heavy concentration of visible matter in a small region. Galaxy as a whole = lower concentration of visible matter, over a larger volume DM = even lower concentration of mass, but over even a huger volume.
  7. Artificial gravity...

    On a small scale station, your flight of stair going from one level to another could look like this.* Now you could align the stair case with the axis of rotation, but then Coriolis effect would try to push you sideways as you climbed or descended. Even with the set up above, you'd want to point the staircase in the correct direction with respect to the rotation. Here you would want the rotation to be clockwise. This way, the Coriolis effect would tend to push you towards backwards( up-stair) when descending the staircase. It would also tend to push you backwards when climbing, but this would probably be easier to deal with while climbing than while descending. If worse came to worse, you could design "up" staircases and "down" staircases curving in opposite directions relative to the spin. (Just avoid trying to go down the up staircase) * I'm learning a new 3-D rendering software, so this is giving me an opportunity to play around with it
  8. Artificial gravity...

    Love the song, but prefer the Noel Harrison version.
  9. Artificial gravity...

    Just for the fun of it, here's the square habitat done with stair steps to make it easier to walk around the interior since near the corners, the slope approaches 45 degrees. The simulated gravity will be ~41% higher at the corners than it is in the middle of each side, so you would be dealing with more "weight" as well as a steeper incline there. Maybe it's just me, but there's something very "Esher-esque " about this image.
  10. Artificial gravity...

    Here's another visualization of what walking around the spinning square would be like, showing 1 full side and part of two others:
  11. Artificial gravity...

    For a person walking around the square, it would be similar to walking from one vee shaped valley to another with a hill in between. Something like this. Though the "hills" wouldn't curve but act more like a flat surface tilting as you walk.
  12. What closes and opens the doors? For instance, is it a force acting on the axis of rotation? If so, then that force can only propagate through the material of the doors at the speed of sound of the doors. For even the most rigid doors, this can't be faster than the speed of light. This means that parts of the door near the axis will start moving sooner than parts further away. And since the closing of the doors are going have to be a significant fraction of the speed of light it is going to be significant relative to the speed of propagation through the doors, and you are going to get a noticeable distortion in the shape of the door. What stops the doors from closing? is it the contact of the red dots?, if so then this can only propagate through the doors at a fixed speed, and different pats of the doors will stop moving at different times. But for simplicity of argument, Let's assume that you've arranged for the doors to act as single rigid objects in the Barn's rest frame. This does mean mean that they will do so in the ladder ladder frame. The Relativity of Simultaneity doesn't just apply to when the doors close and open, but also to different points of the doors. Below we show what happens with the open doors according to the ladder frame (where the barn is moving right to left), and assuming the doors close simultaneously and as rigid objects in the barn's rest frame. The far end of the right door will start moving first, then the points of both doors where they touch and then finally the far left end of the Left doors. Different parts of the doors will start moving at different times. So even if the shape of the doors is not distorted in the barn frame, they will be in the ladder frame. if you doubt this, just consider the following image At the top we show the barn doors as they appear in the open and closed positions in the barn frame. Below that, how they appear in the ladder frame. In both cases in the ladder frame the doors will be length contracted along the left-right direction. However, since they are rotated by 90 degree between the open and closed positions, they have different shapes before and after closing. The element of rotation for the doors while opening and closing add yet another complexity to the problem. Since the vector direction of different parts of the doors change relative to the ladder's motion vector direction during opening and closing, the resulting velocity addition for any point of the door changes from moment to moment in the ladder frame (using relativistic velocity addition). In other words, if a point of the door a given distance from the axis of door rotation has a constant tangential speed relative to the axis as measured from the Barn frame, the ladder frame will measure a changing tangential speed with respect to the axis as that point travels along the path of rotation. These are some of the complexities to the analysis of the scenario you've introduced with your modifications.
  13. Still won't produce a scenario which produces a paradox. For one thing, in the ladder frame different parts the doors will start moving at different times and different speeds. You simply cannot produce a paradox in SR if you properly apply all the principles.
  14. Here's the problem, in the third diagram on the left side you show the ladder just fitting inside the barn with the doors closed, however, this isn't possible. The ends of the doors themselves can't travel faster than the speed of light. In the time the doors go from fully open to fully closed, the ladder will have moved from the left to the right by some amount. Thus for the ladder to fit in the barn while the door are closed and the rod ends have met, the barn must be quite a bit longer, and not just a little bit longer than the ladder. (if you increase the length of the barn to account for the movement of the ladder while the doors close, this means you are moving the doors further apart, which in turn means it takes longer for the rods to meet, causing you make the barn longer.. ) While this doesn't mean that you can't arrange things so that the ladder fits inside with both doors closed and the ends of the rods meeting, but that the ladder id going to have a lot more extra space between the ends of the ladder and the doors. So much so that even when you switch to the ladder frame, the ladder will fit into the barn. Also in the ladder frame, even though the doors will start closing at different times, due to the way that velocities add in Relativity, they won't close at the same speed in the ladder frame and the ends of the rods will meet at the center at the same time. Your apparent paradox only arises because you failed to take everything into consideration. You assumed things would happen in a certain way without doing an actual analysis of all the parameters involved.
  15. Misty concepts

    No. Non-polarized light is a mixture of light waves which oscillate in all possible planes. When it enters a scattering medium these waves will be subject to being scattered. Some light waves will travel further through the medium before they are scattered. in the medium is not a strong scatterer, and the total distance traveled through the medium is short enough, much of the light will make it through without being scattered. If it is a strong scatterer, or the light must travel an extended distance through it, less of the light will make it straight through and more scattered along the way. Any light wave scattered will scatter in a direction that is on a plane that is at a right angle to the plane that the electric field is oscillating in. Since non-polarized light contains waves that are oscillating in all possible planes, you will end up with light waves being scattered in all directions. When you polarize light by passing it through a filter, you are only letting light waves through that oscillate in a limited direction. When this light enters a scattering medium, just like above, it is subject to being scattered. And like above, some waves will travel further before being scattered. But since the direction in which the light waves are oscillating is restricted, so is the directions in which the light waves will be scattered. This is what the video is demonstrating.