[litespeed (OP)]

According to the ever faithfull E=mc2, a massive body increases mass when accelerated. I just wonder if it gravity increases as well?

[Vern]

I suspect it does but I haven't tried to work out the details.

[LeeE]

If you also factor in the apparent foreshortening, which reduces the effective volume and therefore increases its density, then it starts to look as though something that's accelerated to close to 'c' should seem, to a distant observer, to become a black hole.

[litespeed (OP)]

Lee,

Even if it doesn't look like black hole, the red shift would be so dramatic that it might become undetectible. The thing I find intriguing is the possibility of achieving relativistic velocities with normal propulsion methods [ionization etc]. The reason is that at 86 percent the speed of light, the apparent mass gain is either 50 percent or maybe one hundred percent.

So a 1G thruster will be reduced, at most, to .5G thruster. For science fiction purposes, that means future earthings COULD get out of town. Especially since their time clock will be slowed by half at 86 percent. I don't know how steep the mass increase curve is, but a 1G thruster might be able to cut that by another 50 percent in a reasonable period of acceleration time.

On a robotic scale, it seems to me we could send a probe out at relativistic speeds. And begin to get inter stellar reports back within a few years. Of course, as has been pointed out before, space is not empty, and at some speed or another a high speed vehicle could erode.

[Mr. Scientist]

It does. I also believe that charge increases as well, as it being the sole intrinsic mechanism of inertial energy, so charge generates mass - my theory anyhow.

[Pmb]

According to the ever faithfull E=mc2, a massive body increases mass when accelerated. I just wonder if it gravity increases as well?

Yes. It does. The abstract to the article Measuring the active gravitational mass of a moving object, D.W. Olson and R.C. Guarino, Am. J. Phys. 53(7), July 1985

If a heavy object with rest mass M moves past you with a velocity comparable to the speed of light, you will be attracted gravitationally towards its path as though it had an increased mass. If the relativistic in active gravitational mass is measured by the transverse (and longitudinal) velocities which such a moving mass induces in test particles initially at rest near its path, then we find, with this definition, that Mrel = g(1 + b)M. Therefore, in the ultrarelativistic limit, the active gravitational mass of a moving body, measured in this way, is not gM  but is 2gM .

where g = gamma, b = beta = v/c

Think of it like this - Since the inertial mass of a body increases with speed inertial mass is proportional to (active) gravitational mass, and the source of gravity is (active) gravitational mass then the strength of the gravitational field increaseses as well.

On a similar note - since light has inertial mass it too generates a gravitational field. E.g. the inertial mass, m, of a photon is defined by m = p/c where p = magnitude of momentum and c = speed of light. This comes from the defining relationship for inertial mass, i.e. p = mv. Therefore whatever has momentum has inertial mass.

Please note:  By "inertial mass" I am not referring to proper mass, aka rest mass. These are different quantities. Photons have zero proper mass and non-zero inertial mass. This is why a beam of light, where all the photons are moving in the same direction, generates a gravitational field.

It's bit more complicated that that of course. The mathematical object which completely defines mass is the stress-energy-momentum tensor, T. This is the source of gravity in the same way that the 4-current is the source of the electromagnetic field.

[Pmb]

I also believe that charge increases as well, as it being the sole intrinsic mechanism of inertial energy, so charge generates mass - my theory anyhow.

Charge is an scalar quantity (i.e. an invariant) and therefore does not depend on speed. If charge did increase with speed then a body's net charge would depend on temperaure. Since it doesn't then charge does not depend on speed.

[Mr. Scientist]

I also believe that charge increases as well, as it being the sole intrinsic mechanism of inertial energy, so charge generates mass - my theory anyhow.

Charge is an scalar quantity (i.e. an invariant) and therefore does not depend on speed. If charge did increase with speed then a body's net charge would depend on temperaure. Since it doesn't then charge does not depend on speed.

But then a paradox arises. It is true to say that charge does not depend on speed, but it'sm partially-true if you state that the presence of matter insists the presence of a charge. So really charge does depend the masses speed, since the larger the mass, the larger the gravitational charge, so there are certainly invariant relationships which i feel have not been investigated properly.

[LeeE]

Lee,

Even if it doesn't look like black hole, the red shift would be so dramatic that it might become undetectible. The thing I find intriguing is the possibility of achieving relativistic velocities with normal propulsion methods [ionization etc]. The reason is that at 86 percent the speed of light, the apparent mass gain is either 50 percent or maybe one hundred percent.

So a 1G thruster will be reduced, at most, to .5G thruster. For science fiction purposes, that means future earthings COULD get out of town. Especially since their time clock will be slowed by half at 86 percent. I don't know how steep the mass increase curve is, but a 1G thruster might be able to cut that by another 50 percent in a reasonable period of acceleration time.

On a robotic scale, it seems to me we could send a probe out at relativistic speeds. And begin to get inter stellar reports back within a few years. Of course, as has been pointed out before, space is not empty, and at some speed or another a high speed vehicle could erode.

Umm... redshift will only occur if it's traveling away from us; if it's heading towards us it'll be pretty bright (assuming that it's radiating)

The problem with reaction engines is the amount of fuel required, and which needs to be carried.  You can either burn the fuel quickly and get high thrust for a short period of time, or burn it slowly, at relatively high exhaust speeds, and get low thrust (much below even 0.5G) for a long period of time.  Even with ion-drive motors though, the thrust you get is way below 0.5G and they'll still run out of fuel before they approach relativistic speeds.

Light-sails don't really need any fuel, but they lose thrust with distance from their launching star, and possibly the only real solution is a Bussard Ramjet type engine, which scavenges its fuel from the interstellar medium using a very large diameter i.e. between kilometres and thousand-kilometer+ sized electro-magnetic scoops.  Incidentally, the scoops also help deal with the erosion issue.

Have a look at http://en.wikipedia.org/wiki/Bussard_ramjet for more info if you haven't already heard about them.

[litespeed (OP)]

LeeE - You wrote: "The problem with reaction engines is the amount of fuel required, and which needs to be carried."

[LIGHT BULB OVER MY HEAD]
I just now remembered hearing that each individual cosmic ray carries the same energy as a tennis ball at one hundred miles per hour. Accordingly, the biggest variable for reaction fuel is not the amount of fuel itself, but the EXIT velocity of matter.

Assume a nuclear powered linear accelerator in your 'starship'.  All of a sudden you have reduced the issue to an ENGINEERING problem. Specifically, if you accelatate a particle to near the speed of light you actually create mass as you accelerate it out the back of your ship. A powerful enough linear accelerator will end up pushing a huge amount of mass [relative to what was injected into the accelorator] out the back.

[Madidus_Scientia]

A powerful enough linear accelerator will end up pushing a huge amount of mass [relative to what was injected into the accelorator] out the back.

You'd be creating mass by losing mass. The energy comes from the mass of the nuclear material.

[litespeed (OP)]

Madidus_Scientia - You wrote: "You'd be creating mass by losing mass. The energy comes from the mass of the nuclear material." 

Very good, grasshopper! Energy can neither be created nor destroyed, it only changes form. Give me a good enough linear accelerator, a good enough nuclear reactor, and I convert mass in the reactor, to electromagnetic forces in the accelerator, to acceleration and increased mass out the back side of my 'starship'.

I doubt I will achieve the velocity/mass of a Cosmic Ray, and shoot it out my back side. But that IS the Gold Standard.

[Mr. Scientist]

Madidus_Scientia - You wrote: "You'd be creating mass by losing mass. The energy comes from the mass of the nuclear material." 

Very good, grasshopper! Energy can neither be created nor destroyed, it only changes form. Give me a good enough linear accelerator, a good enough nuclear reactor, and I convert mass in the reactor, to electromagnetic forces in the accelerator, to acceleration and increased mass out the back side of my 'starship'.

I doubt I will achieve the velocity/mass of a Cosmic Ray, and shoot it out my back side. But that IS the Gold Standard.

No. You are both incorrect with that assumption. The first law of thermodynamics breaks down when quantum mechanics introduces the zero-point energy field.

[Madidus_Scientia]

How so?

[Mr. Scientist]

Because the ZPF allows for virtual particles to appear from the vacuum - this happens all the time, so it seems energy can be created.

[Madidus_Scientia]

And what does this have to do with nuclear powered particle accelerators?

Anyway, my understanding is that they appear in particle/anti-particle pairs, and the energy of the system remains constant, in line with the conservation of energy.

[litespeed (OP)]

Mr. S

I stand corrected; however, give me a good enough nuclear reactor, a good enough linear accelerator, and I will STILL spit relativistically dialated matter out my backside...and go FAST!

[LeeE]

Equivalent energy needs to be put into accelerating the relativistically enhanced mass as you get out from from using it: TANSTAAFL

[Mr. Scientist]

And what does this have to do with nuclear powered particle accelerators?

Anyway, my understanding is that they appear in particle/anti-particle pairs, and the energy of the system remains constant, in line with the conservation of energy.

Virtual particles do not always have the laws. The reason to that is very lengthly, but in a nutshell E=Mc^2 where The equation relating energy, mass and momentum in special relativity is:

E^2 = p^2c^2 + m^2c^4,

In the special case of a particle at rest (i.e. p = 0), the above equation reduces to E2 = m2c4. Because virtual particles do not posses a real matter then the mass and momentum relation fails, and is reduced specifically. In a deeper note, spontaneous symmetry breaking is also a form of violation where the solution E=\pm Mc^2 is not always true.

[Mr. Scientist]

And what does this have to do with nuclear powered particle accelerators?[€/b]

Anyway, my understanding is that they appear in particle/anti-particle pairs, and the energy of the system remains constant, in line with the conservation of energy.

Why not.. acceletators are designed to be exactly like the condition of a vaccuum. My statements so far have been very applicable, i believe anyway.