Quiz about FTL galaxy observations

[Helio]

Here's a question I have that may help with understanding how light emissions from galaxies can reach us even though they are moving away from us (carried by space) faster than the speed of light.

If you can throw a snowball at 40 mph and a bus passed by you at 50 mph, can you throw ever hit the bus if you throw it after the bus has passed? [You are allowed to have others in the snow doing things around you.]

 

[billslugg]

False premise. We cannot see light emitted by galaxies moving away from us FTL. As they get farther away and move faster and faster they turn red, then infrared, then radio waves of longer and longer wavelength. Once they are going the speed of light all we see is black. At FTL speeds we also see nothing.

 

[promytius]

We will see them because the light from the time their speed/distance became unviewable has not reached us yet; otherwise we'll never know about any further away/faster moving galaxies.

 

[Classical Motion]

A spot at FTL might be blind, but a long enough length might interact long enough with sideways light for to see. A large collector. Radial light sources, should have some duration at fly by.

 

[Helio]

False premise. We cannot see light emitted by galaxies moving away from us FTL. As they get farther away and move faster and faster they turn red, then infrared, then radio waves of longer and longer wavelength. Once they are going the speed of light all we see is black. At FTL speeds we also see nothing.

That would be true if it were a Doppler model. It’s not. Hence the “cosmological redshift” describes it.

At only ~ z=1,4 galaxies are moving from us faster than light, though being carried by space. The CMBR is at z=13.8. The CMBR is receding at 1,090x the speed of light.

Here is Ned Wright’s calculator revealing details.