Janus

Scientists believe it possible for silicon based life forms to exist.

While there has been some speculation on the possibilty of silicon based life, I don't think that any positive conclusion of it possibility has been reached. In fact, most of the evidence points against it.

Example: carbon dioxide is a gas at standard temp and pressure, silicon dioxide is a solid. The same is true for other silicon based molecules. This means that silicon based molecules tend to be less reactive. In order to form life you need chemical reaction to take place.

A way around this is to place the molecules in a warmer enviroment, meaning you would need a hot planet for silicon life. The problem is that you also need complex molecules for life, and molecules made from silicon chains are more fragile than those made from carbon. The upshot is that the conditions needed for the molecules to be reactive enough for silicon based life to exist are too harsh to allow the formation of the complex molecules needed for life.

The trick to all this is the rocket equation.

v_f = v_ex ln( M_i/M_f)

The part within the parenthesis is known as the mass ratio, and is the ratio of the fully fueled rocket to the rocker empty of fuel.

for any given mass ratio, the final velocity of the rocket depends on the exhaust velocity. the higher the exhaust velocity the greater final speed your rocket can achieve with the same amount of fuel. In other words, higher exhaust velocity leads to better efficiency.

The ion rocket is more efficient that the chemcal rocket because it is capable of producing higher exhaust velocity. The downside is that Ion drives produce a "thin" exhaust (The total amount of exhaust it can produce in a given amount of time is low), this leads to low thrust and slow acceleration.

Falling somewhere between is a system under development called a VASIMR (VArible Specific Impulse Magnetohydrodynamic Rocket)

It is more efficient than chemical rockets, while producing more thrust than ion rockets. It is also adjustable so that you can choose either the highest efficiency or the most thrust, depending on the what you need at the moment.

Lmao, I'm just going with what my science teacher taught us....he says proxima centuari is the closest star to us, and has it's own planets, wow, guess not.

Well, Proxima (Alpha Centauri C) is the closest star, but it is unknown as to whether is has any planets. It is a small red dwarf that is part of the Alpha Centauri system which also includes Alpha Centauri A & B.

'A' is a yellow star of about the same mass as the sun, and could have planets in the habital zone, but it is unknown as to whether it does.

Speaking of which, where are Voyager 1 and 2 now? Can they still send pictures or are they just defunct peices of metal floating around out there?

http://web.mit.edu/space/www/voyager/voyager.html

 

Edit: To clearify' date=' does time pass 60 microseconds faster per day in the center of Earth relative the surface ?

[/quote']

No, time runs slower at the center of the Earth. Gravitational time dilation is related to the difference in gravitational potential, or how "deep" you are in the gravity well. The center of the Earth is deeper in Earth's gravity well than the surface. If you were to drill a hole to the center of the Earth and were at the bottom, you would have to do work to climb back out to the surface. Just like you would have to do work to lift yourself a given distance above the center of the Earth. It is this amount of work that determines the time dilation between positions in the gravity field, not the relative local strength of the field at those positions.

If observers in two inertial frames' date=' A and B, moving relative to each other "see" each other's clocks as moving slower than their own clock then should not the application of "reciprocity" be imposed. If observers on both frames assume their motion is at rest wrt the other, then should not the clocks manifest this simple reality of SRT? I mean if both clocks are started and stopped at the same instant then the clocks should reflect the SRT reality of time dilation shouldn't they?

 

Geistkiesel[/quote']

 

Relativity of Simulataneity. The clocks can only stop at the same instant according one frame, A or B. According to the other frame the clocks do not stop at the same instant.

Example: if the time dilation factor is 2, and the clocks stop at the same instant according to frame A, then from A, clock B will read 1/2 the value of clock A because clock B was running half as fast.

 

From B, clock A will run half as fast as clock B, but the two clocks do not stop at the same instant. Clock B stops, and then some time later when it finally reads twice the value of the stopped B clock, Clock A stops. Thus both frames agree as to what both clocks read when they are stopped.

Go to

http://ssd.jpl.nasa.gov/cgi-bin/eph

Choose the target as the Sun. Set the date/time range you want. Generate the ephemerides.

The distance to the sun will be under the heading "delta" and in AU. One AU is 149,598,550,000 meters.

A graviton would be a quantum of gravitational raditation, in the same way that a photon is a quantum of electromagnetic radiation. And just like the virtual photon is the mediator for the electromagnetic force, it is the virtual graviton that would mediate gravity.

This is assuming that gravity can be quantisized.

As much as I may have botched up what I did I think 125 newton metres is right. Is that the same as 125 joules or 125 watt seconds? One of us is off by a few decimal places.

Its me, I forgot to convert the meter/sec to cm/sec before plugging the numbers in.

It would be 125 watt-sec, .03 watt-hrs, run a 100w bulb for 1.25 secs, etc.

I was thinking in terms of power dissipation in watts upon the projectile hitting the target' date=' some will be sound, some heat, some in projectile fragmentation etc...

 

so watts is a good unit to use (I think?).[/quote']

 

You are not going to like this, but, The dissipation in watts also depends on the distance over which the projectile stops.

 

What does not depend on the stopping distance is the energy of projectile. The energy of your projectile is 125000 ergs, which is equal to .0125 watt-sec or .000003 watt-hours. This is about the amount of energy it takes to light a 100w light bulb for 125/1000000 of a sec.

 

A watt-sec is equivalent to one watt for one sec. In your example, if the projectile stops in 1 millisec it would need to disipate at a rate of 12.5 watts for 1 sec.

 

If it took .5 millisec to stop, it would disipate at a rate of 25 watts for .5 millisec.

 

So if you are interested in the property of the impact that does not change with stopping distance, then you need to deal with energy, which is measured in ergs, joules, watt-sec, kilowatt-hrs, calories, therms, BTUs, horsepower-hours, electron-volts etc.

erm... lets no go the speed of light and stuff eh' date=' I really did want to keep this straightforward and in Laymans terms as much as possible!

 

so Janus, if a projectile is say 1 gram and moving at a rate of 500 metres per second and then hits a brick wall, what force does it hit with ?(please ignore drag coefficients of air resistance and other trivia I can`t even begin to think of).

 

as well as the answer can you tell me what formula you used and show your working out please.

 

Thanks [/quote']

 

Again, the force would depend on how far the projectile penetrates into the wall before in comes to a stop.

No, Mass x velocity is momentum.

The force imparted in an impact is related to the "stopping" distance of that impact, which in turn is related to the stopping time, and that in turn is a measure of acceleration.

I.E. It takes ten times more force to stop a bullet over a distance of 1 mm then it does to stop it over 1 cm. Of course it takes the same energy to stop the same bullet in both instances, as energy is force times distance.

As stated above, the speed of sound in a gas is:

[math]v= \sqrt{\gamma R T}[/math]

Gamma is the Ratio of specific heats

R in the gas constant

T is the Temp in Kelvin.

For air:

Gamma = 1.4

R = 286

For CO2:

Gamma = 1.3

R= 189

From this it is obvious that sound travels faster in air. (330 m/s vs 259 m/s at 0 degrees C)

 

The two earths do not fall together at 2g=9.8+9.8 = 19.6 meters per second squared.

Yes, they do. Your calculations only took into account the acceleration of M1 due to its attraction to M2, but neglected the acceleration of M2 due it's attraction to M1.

Mark' date=' suppose that two twins are in a space station which is in orbit about the earth.

 

Now, each is floating weightless, and they are in the same inertial reference frame, and they are aging equally rapidly.

 

Let each of them have an identical wristwatch on.

 

Now, let one of the twins accelerate in some direction.

 

 

Thus, one of the twins is still at rest in the original inertial reference frame S.

 

Let the direction of the acceleration in this frame be in the i^ direction. That is the direction of increasing x coordinate in the frame.

 

Now, don't worry about the direction of the accleration anymore, focus on the magnitude of the acceleration.

 

Denote the magnitude of the acceleration by a.

 

The magnitude of the acceleration is the time rate change of speed in the frame.

 

Speed in a frame is distance traveled/ corresponding time of travel

 

Let v denote the instantaneous speed of the twin who is accelerating in the original frame, frame S.

 

Therefore:

 

[math'] a = \frac{dv}{dt} [/math]

 

The equation above is a scalar equation, we aren't worrying about direction of relative motion at all right now.

 

Now, here is the time dilation formula:

 

[math] \Delta t = \frac{\Delta t^\prime}{\sqrt{1-v^2/c^2}} [/math]

 

Let S` denote a reference frame which is permanently attached to the twin who accelerates in frame S.

 

 

Thus, the speed of frame S` in S is the v in the formula above.

The symbol c denotes the speed 299792458 meters per second.

Now, consider an event which begins when the twins are together, and ends when the twins are 50 light years apart.

 

According to the time dilation formula:

 

Dt is the amount of time that passes according to the watch at rest in S.

 

Dt` is the amount of time that passes according to the watch at rest in S`.

 

As you can see, they are not equal according to SR.

 

Specifically more time passes in S, than passes in S` for the same event.

only as measured by S'

 

 

Now, the formula above does not involve the acceleration a of the ship, it only makes reference to the instantaneous relative speed v.

 

So if you look at things from the point of view of the twin in frame S`, he sees his brother accelerate away from him at speed v as well.

No, he can easily tell that he was the one who actually accelerated. He can feel the acceleration, he can fire a laser perpendicular to his path and notes that it curves, etc. And while the time dilation formula holds when used by either twin while they are at constant velocity, and holds for the twin that does not accelerate (remains in the same reference frame the whole time.),

It is incomplete for the twin who undergoes acceleration while he is accelerating. For him he has to add an additional transformation that takes into account his acceleration and the distance between himself and his brother.

 

So yes there is a paradox created.

 

The logical conclusion is this...

 

If the time dilation effect can happen, it can happen in at most one of these two frames, not both. In other words, the formula cannot be true in both reference frames.

 

Regards

No, it is not. Again you must take all the effects involved into account to properly address this. In fact, when you do take them into account, the time dilation formula must be applied in [/i]all[/i] frames in order for there not to be a paradox.

I would strongly urge you not to try and explain Relativity to others, you do not grasp it properly yourself.

The objects in question are the Earth and Moon, right? While I appreciate you pointing me towards a fuller mathematical understanding of gravity, this thread is about two specific bodies and their relationship. So can I assume that my earlier remark about the moon deriving it's pull from the Earth was accurate, or not?

No, that remark was not correct.

Let's see if we can make things clearer. The force acting between two bodies is equal to the formula given already:

[math]F= \frac{GMm}{d²}[/math]

G is the universal gravitational constant.

M is the mass of one body and m the mass of the other

d is the distance between their centers.

Using this we can calculate the force between the Earth and a 1kg mass sitting on its surface:

The radius of the Earth is 6,378,000 m so this is d

The mass of the Earth is 6 x 10^24 kg

so we get:

F= [math]F = \frac{((6.673 x 10-11)(1)(6 x 10^{24})}{6,378,000^2}=9.8N[/math]

For the Moon,

Mass = 7.35 x 10^23kg

radius = 1,735,000m

So the force acting on the same 1kg weight sitting on the Moon is:

F= [math]F = \frac{((6.673 x 10-11)(1)(7.35 x 10^{22})}{1,735,000^2}=1.6N[/math]

1/6th that of if it was sitting on the Surface of the Earth.

So we can see that even though the mass of the Moon is only 1/81 that of the Earth, an object sitting on the Moon's surface is is less than 1/3 as far from the Moon's center than an object sitting on the surface of the earth is from the Earth's center is. This is why the force of gravity on the surface of the Moon is 1/6 that of that on the surface of the Earth.

That's like asking:

If Unicorns really existed, would their horns actually be an aphrodisiac?

Let me ask you one question.

 

Do the experiments prove that c is constant in all inertial reference frames.

OR

 

Do these experiments prove that the speed of any photon relative to that which emits it' date=' is c, regardless of material.

 

Which one?[/quote']

 

The first one.

Ok then a followup question. Does classical EM predict this?

Yes.

Someone said that if you throw a magnet around (presumably against hard surfaces) the magnet will begin to lose its magnetism... the impact effects the magnetic domains or something...

 

Is this true?

A magnet is a magnet because of two things:

1. the indivdual atoms/molecules have a magnetic moment(due to an imbalance of the spins of the electrons each atom has a net magnetic field.

2. These moments are aligned. (the magnetic fields of the atom all point in the same direction.) And thus re-enforce each other.

If you strike a magnet sharply, you "dislodge" some of these atoms out of alignment and randomize them so that they no longer add to, and to some extent cancel out the total field of the magnet.

The same thing happens if you heat a magnet. As you heat it, the atoms vibrate. Heat it enough and the atoms will vibrate right out of alignment, and you will demagnetize your magnet.

What I really want to know is whether or not Newton's third law holds in this case.

 

Consider the jumping ring demonstration' date=' there are videos of it on the web.

 

You can't see anything, other than the ring soaring upwards.

You cannot see what is pushing the ring up.

Whatever is interacting with the ring, isn't connected to the solenoid when it interacts with the ring. So it's not immediately clear to me anyways, that there is a reaction force down on the solenoid.

 

I've never done the experiment myself, and it's a simple one to do. In fact one could do it in the space shuttle, and immediately know the answer.

 

Connect the ring to a solenoid, let the apparatus float in the cargo bay.

Then turn on the current.

 

Either the whole apparatus will accelerate relative in the cargo bay, or not.

 

So which is it?

 

I personally don't know the answer, but since the question is empirical, I figure someone already knows.

 

Giant supercolliders use the technology, so what's the answer?[/quote']

 

The answer is this. When you turn on the solenoid, it induces eddy currents in the ring. These electrical currents turn the ring itself into a magnet which is repulsed by the magnetic field of the solenoid. This is shown by the fact that the more conductive the ring, the higher it will jump and that if the ring is not complete, it will not jump.

 

The jump is caused by simple magnetic repulsion, and the ring repels the solenoid just as much as the solenoid repels the ring. They push against each other. If you were to place them floating in space, the ring would fly in one direction and the solenoid would recoil in the other.

 

You don't even have to go out into space to demonstrate this, just place the solenoid on a sensitive scale and note how the scale registers an increase of weight when the ring jumps off and the scale absorbs the force of the solenoid's recoil.

Your backpack is permanently connected to your suit' date=' and it happens to contain a solenoid, which is permanently connected to it. You have a space-tool which is a ring in shape, which just happens to fit around the solenoid, and some space-tape, so you can tape the ring to the solenoid if you wish. You have a switch which can turn the battery to the solenoid on or off, attached to a guage.

 

So the only thing you can throw, is the ring.

 

The mass of the ring is such that if you throw it with your maximum force, you will reach the ship in 11 minutes, so that's out. What do you do?

 

 

PS: The tape is effectively massless.

 

[/quote']

 

You lose the tape, point the solenoid towards the ship, hope that the ship is ferromagnetic and that the solenoid is powerfull enough to pull you to the ship in under 10 min.

 

Or, you could wrap some tape around the ring, sticky side out, Leaving your self about 20 ft of lose tape(folded in half lenghwise so it won't stick to itself) or conversely, unwind about 20 ft of wire from the solenoid. Gently toss the ring towards the ship, and hope that it adheres to the ship stongly enough to allow you to pull yourself to the ship in less than 10 min. (assuming you and your suit mass about 100kg, then that adhesion would only have to resist about .0033 Newtons)

 

But if you are hoping to build some reactionless drive with this stuff that will move you to the ship, then you're betting on a dead horse and will soon be dead yourself.

By "rotating at .25c" I'm goin to assume that you mean that the outer edge of the disk is moving a .25c.

This is simply another example of the Relativistic addition of velocities, namely that velocities do not add by the relationship of

[math]w=u+v[/math]

but by

[math]w=\frac{u+v}{1+\frac{uv}{c^2}}[/math]

In this case, your second disk would rotate at

[math]\frac{.25c+.25c}{1+\frac{(.25c)(.25c)}{c^2}} = .4c[/math]

relative to you.

Meaning that if the second disk was rotating at .25c relative to the first disk as measured from the first disk, then relative to you, it would move at .4c.

if I add a third disk moving at .25c relative to the second it would be moving at

[math]\frac{.25c+.4c}{1+\frac{(.25c)(.4c)}{c^2}} = .559c[/math]

forth disk:

[math]\frac{.25c+.559c}{1+\frac{(.25c)(.559c)}{c^2}} = .778c[/math]

fifth disk:

[math]\frac{.25c+.778c}{1+\frac{(.25c)(.778c)}{c^2}} = .988c[/math]

sixth disk:

[math]\frac{.25c+..988}{1+\frac{(.25c)(.988)}{c^2}} = .993c[/math]

seventh disk:

[math]\frac{.25c+.993c}{1+\frac{(.25c)(.993c)}{c^2}} = .996c[/math]

eighth disk

[math]\frac{.25c+.995}{1+\frac{(.25c)(.995c)}{c^2}} = .997c[/math]

ninth disk

[math]\frac{.25c+.997c}{1+\frac{(.25c)(.997c)}{c^2}} = .998c[/math]

tenth disk

[math]\frac{.25c+.998c}{1+\frac{(.25c)(.998c)}{c^2}} = .999c[/math]

eleventh disk

[math]\frac{.25c+.999c}{1+\frac{(.25c)(.999c)}{c^2}} = .9994c[/math]

twelveth disk

[math]\frac{.25c+.9994c}{1+\frac{(.25c)(.9994c)}{c^2}} = .9996c[/math]

notice that each successive disk's velocity increases by a smaller and smaller amount.

No matter how many disks you add the last disk will always move at less that c relative to you.

If on the other hand you try to arrange it that each disks velocity increases by .25c as measured by you, then each disk will have to rotate faster with respect tot he last disk as measured by that disk.

for instance if you want the second disk to rotate at .5c as measured by you then the second disk woud have to rotate at .286c realtive to the first disk as measured from the first disk.

The third disk would have to rotate at .4c relative to the second in order for it rotate at .75 c as measured by you.

And the fourth disk would have to rotate at 1c relative to the third to reach 1c as measured by you. But since the third disk cannot rotate at 1c relative to the third, this can never happen.

In short, the only way for the last disk to have a velocity greater than c relative to you is that at least one of the disks to have a greater than c velocity relative to the disk it rests on.

It doesn't matter is each disk rotates at .001c or .25c relative to the one before, the answer comes up the same; you can't acheive FTL speeds this way.

Well yes there is' date=' they have the same special fundamental speed, with respect to the source.

 

Regards[/quote']

 

Which means that they have one property in common (zero rest mass). One shared property is no evidence of being the same thing.

 

The proton and positron share the same property of charge, that doesn't make them the same thing. The electron and muon share three common properties, even that does not make them the same thing.

Considering that the critical mass of Plutonium is only 2/3 lb, 2lbs can cause you a lot of damage as it goes BOOM!.( In reality the reaction will probably fizzle and not undergo complete fission, but even a fizzled chain reaction would not do you any good at close range.)