Jacques

Me too I think that because in the gamma factor equation speed is squared

No. The Mach effect is a case of the Doppler effect. The applet is cool!!! Remark that it illustrate very well the Cherenkov radiation. To understand the Doppler effect set a speed < 1 and imagine that you are a stationary observer on the screen. If you are to the right of the screen you will see the source moving toward you and you will see wave front reaching you by unit of time (blue shift). If you imagine yourself to the left of the moving source less wave front will reach you by unit of time (red shift) My original question was about the combination of 2 effects of a moving source of wave: 1 Time dilatation: time in a moving source slowdown for an outside stationary observer. So the frequency of a radiation will look lower or redshifted. Note that the slowdown is independent of the direction of the moving source relative to the observer. 2 Doppler effect: the frequency of a source will look lower when the source is moving away (redshift) and it will look higher when the source is moving toward the observer (blue shift). So I was wondering if the combination of the two effects (redshift of time dilatation and blueshift of Doppler effect) could cancel each other in the case a moving source toward the observer. From the equation we can see that the Doppler effect is always bigger than the time dilatation so the cancellation of the 2 effect is impossible. Thanks again for your answers

I thaught htat Basic evolved to Visual Basic. Also don't speak of compiler when speaking of Basic. It's an interpreter that run the code. I like interpreted language for developpement and prototyping, but when you need performance you need a compiled program.

Johnny5 There are many way to define dimension. One definition is: dimension is the number of variables needed to describe a quatity. For example space need 3 variables to be defined (x,y,z). In relativity time is one dimensional (t) . Colors models use on computer and television are 3 dimensional (Red,Green,Blue) □h=-16πT I will do some reading on that. I found that link on google http://www.voting.ukscientists.com/interva.html Here is a link that consider time as a vector http://members.triton.net/daveb/ What do you think of this site ?

Isn't it the 4th dimension in relativity ?

Exactly that time is more than 1 dimensional and my feeling is that it is 3 dimensional.

When I look at the gamma factor in relativity equations, I always see the Pythagore theorem [math]\gamma=\sqrt{1-v^2/c^2}[/math] If we take c for unit of speed we get [math]\gamma=\sqrt{1-v^2/1^2}=\sqrt{1-v^2}[/math] and [math] 1=1^2 [/math] so we can write [math]\gamma=\sqrt{c^2-v^2}[/math] [math]\gamma^2=c^2-v^2[/math] [math]c^2=\gamma^2+v^2[/math] When the gamma factor is applied to time, it make me thinks that time is more than one dimentionnal. What do you think about that ?

66.5= 90 - 23.5

Not exactly motion is more fundamental. Time is one aspect of motion. Space is the other aspect of motion.

The first external relative to earth The last internal relative to asteroid belt

You will find a good description of the coordinate system used in astronomy. http://csep10.phys.utk.edu/astr161/lect/time/coordinates.html The letter of the greek alphabet denote the stars of the constellations in descending order of apparent brightness. So alpha polaris is the brightess star in the polaris constellation. Brightess is mesured with unit of magnitude. http://www.heavens-above.com/gloss.asp?term=magnitude Often the size of the dot representing the star on sky chart represent the magnitude

I found these sites : http://repairfaq.ece.drexel.edu/sam/lasercon.htm http://www.edu.linkoping.se/bit2a/laser/homemade/CONSTRUC.htm

Time exist only has the denominator of motion. You cannot have time without motion. If motion didn't exist then time wouldn't exist.

It is a unit of time.

It is just a scale factor without unit. Length is also contracted but you don't conclude that lenght have a speed...

Here you can find an easy to use star chart generator http://www.fourmilab.ch/yoursky/

What is the unit of time ? I can accept something like "Time progress" or thing like that, but by definition time does have a speed . Time is only a component of speed.

Maybe I should start a new thread on that but looking at the equation on the redshift bring an other question in my mind: In other thread I read that distant galaxies doesn't have proper motion, there apparent motion is caused only by the expansion of space. My question is why does the time dilatation component is include in the redshift equation ?

Speed or motion is space over time. You can not tell time have a speed. Time is a component of speed.

Here is a link that explain relativist redshift. http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/reldop2.html#c1 The only solution for source equal observed frequency is for v=0 I think also that there might be some solution for source going with an angle toward the observer. Thanks for your answers

Time dilation will redshift the spectrum of an radiating object moving relative to the observer. Also the motion of the object will redshift (if the object is moving away) or blueshift (if the object is moving closer) it spectrum because of the Doppler effect. For an object moving toward the observer, is there a speed where the redshift cause by time dilatation will be compensated exactly by the Doppler blue shift ?

I disagree. You don't give a hint of how gravity would be mediated by photon...

The links in the page http://members.triton.net/daveb/ Doesn't work. For example: http://toe.sytes.net:65333/Introduction.htm Give me: The page cannot be displayed

To go faster than the wind you need a centreboard under your boat

Yes