Jacques

He doesn't see himself traveling into the future because he see himself traveling into the pass.

Particle collider mostly use electron-electron or nucleus-nucleus for there experiment. There is a conservation law about the electric charge. Does these experiments are biased by using particle with the same electric charge ? For example if you collide proton with proton the result should be mostly positive charged particle. Just a thought...

That is a kind of problem that cost a lot : http://www.wired.com/2010/11/1110mars-climate-observer-report/

Thanks for your answer and interest. The basic idea is somekind of mass driver, expelling some mass (water vapor) from the comet, but without all the mechanical part. I thaught of using nuclear power because of the higher power density, but it seam that you cannot control a nuclear reactor without some complex feedback mechanic. Maybe it would be possible to have a subcritical mass and have a neutron source turn on when in place. I was targeting the pole so it can work all the time.

Swansont Does a nuclear reactor is critical or is it subcritical ? Can we used some uranium mixed with some moderator and have it warm enough but not explose ? Maybe I used a to hight temperature, but the idea is transform the ice into steam to propel the comet.

Hi I had an idea that might interest some people here, and I would like to have some comment on that idea. There is a possibility that someday we will find a comet heading to earth and we will try to deviate it so it miss the earth. There are many senario's proposed, but mine is so simple: Take a big mass of nuclear fuel and crash it on one of the pole of the comet. Make it crash at a speed so the mass will penetrate between 10 and a 100 meter. The nuclear mass is subcritical so it wont detonate, but massive enough to come to a temperature of around 1000 Celsis. The interior of the comet is mostly water ice and the water will turn into steam that will exit by the entry hole providing some trust. Is it a realistic scenario to change the orbit of a comet ? How much fuel would be needed ? How long before the hole get to large ?

So if the universe was 44 million light years across, we should have received that light a little bit more than 44 millions years latter even with the expansion of space. So the CMB is not photon directly received from that era but more echo.

What was the size of the universe at that time ? I don't know, but it must be a lot smaller than today, and I can suppose that the CMB had time to pass by us. May be the CMB we detect now is just the echo of the photon that was absorbed and reemited and reabsorb etc...

Hi I didn't read all the posts and I don't know how the subject is now the twin paradox, but I have some taught about the original question: When a photon is released, which way does it head?Some photon are realesed by excited atoms. Considering the law of conservation of momentum we can imagine a situation where we can predict the direction of the released photon. Consider an atom at temperature close to 0K so it can be considered stationary. Shot a photon from the left on that atom. If the atom absorb that photon , the conservation of momentum tell us that the atom will be moving to the left. After a while the atom is de-exited and emit a photon of the same momentum as the incident one, so the photon will continue in the left direction and the atom will stop. Is it theoriticaly correct ? Is it pratically correct ? (I guest that we cannot have a stationary atom because of Heiseinberg uncertanity) Just a thaught

If it was real, it would be on the market and the inventor would be rich.

Thanks for the link. But would it be correct if it was a collision between two proton beam , instead of a proton beam hitting stationnary proton ? Very hard to explain how it is happenning, specialy for proton antiproton because they are composed of 3 quarks. I can speculate that there is an intermediate state where the is some gamma ray of hight energy. We can try to simplify the question with electron-positron creation by a gamma of 1.1Mev. But we don't know how it is happening to. I can speculate some self-interaction of the magnetic and electric field of the gamma photo to create 2 loops . One for the positive phase of the photon and the other one for the negative phase... I don"t know if I remember well but I read that a 1.1Mev will not spontanously transform in the electron-positron pair. The photon need to pass by a heavy nucleus...

OK Thanks I know that antimatter is observed. The complete equation for antiproton creation is: [math]p^+ + p^+ + 2(m^pc^2)\rightarrow p^+ + p^+ + p^- + p^+[/math] where [math]m^p[/math] is the mass of the proton

Thanks for your answers. I thought that it still a theory and that there were no observation of that violation. The idea of antimatter being matter going back in time is untestable, but can explain some particle process with Feynman diagram, and the matter-antimatter asymetrie. Why should we discard that idea ? Thanks

Hi Where is the antimatter ? During the Bigbang the energy 'condensed' into matter and antimatter. If we accept the Feynman–Stueckelberg interpretation of antimatter, that antimatter are particle going back in time, then there was nothing before the 'condensation' so the antimatter never encontered matter. Anti matter that was created in that time are going back in time and will never meet matter. Is it something that was thaught before ? Thanks

Thanks for you link.