Another speed of light question

[matheinste]

Quote:-

----I think it's red-shifting taken to extreme. After c the wavelength goes infinite. Here again the spaceship has to be going away from the observer not across his line of vision. -----

There is no after c.

Matheinste.

 

[Nickelodeon]

Quote:-

----I think it's red-shifting taken to extreme. After c the wavelength goes infinite. Here again the spaceship has to be going away from the observer not across his line of vision. -----

There is no after c.

Matheinste.

Yes there is - you just need some Hubble Flow to help you along

 

[matheinste]

Hello nickledoeon

Quote:-

---Yes there is - you just need some Hubble Flow to help you along ---

I believe Hubble flow is to do with recession of objects due to universal expansion. i do not think it involves anything actually moving at greater than c relative to something else.

Just a thought. If you are aware of things such as Hubble flow, how do you not understand the very basics of SR.

Matheinste

 

[lightarrow]

What part exactly of what he is saying is physically nonsensical?

Define an object's velocity and you'll have the answer.

That "speed of separation" corresponds to the velocity of which object, in physics?

 

[lightarrow]

No. Unless I'm mistaken though, an external observer looking at the craft as it whizzes by would be measuring its relativistic mass.

Relativistic mass doesn't exist. Only invariant mass = mass. If then you want to say that accelerating m from 0 to 1000 m/s requires less energy than accelerating it from 1000 m/s to 2000 m/s, that's another story: F = m*a doesn't hold in relativity.

 

[Nickelodeon]

Relativistic mass doesn't exist. Only invariant mass = mass. If then you want to say that accelerating m from 0 to 1000 m/s requires less energy than accelerating it from 1000 m/s to 2000 m/s, that's another story: F = m*a doesn't hold in relativity.

Surely relativistic mass = invariant mass plus the mass equivalence of its relative kinetic energy so how can you say it doesn't exist?

 

[lightarrow]

Surely relativistic mass = invariant mass plus the mass equivalence of its relative kinetic energy so how can you say it doesn't exist?

Because it's completely meaningless, unless you call it "Energy". The only meaningful mass is invariant mass, so that's the only mass you should talk about.