How Fast Must Something Be Moving Away For Detection To Become Impossible?

"Perhaps dark matter is just stuff moving so fast that we have no way of detecting it."

Where's it going?

As long as it isn't moving this direction, I don't really care.

Maybe it's dark energy being compressed by the Galactic giant Black Hole at the center causing it to move beyond the speed of light....

Why would everything be moving away from us? What is special about our place in the universe?

Our position in the universe is not special. You would expect that if there were a significant number of objects moving at almost light speed that we would see some approaching, some passing by and some receding, so you would see a range of doppler shifts ranging from blue to red. This is not the case.

I think there are a few instances of blue Doppler shifts (approach of Andromeda, for instance), but mostly red shifts.

I sort of think of God as being a type 4 being on the Kardashev scale.

We being ~.72.

Those harnessing the power of a whole planet. Type 1.

Those harnessing the power whole star Type 2.

Those harnessing the power whole Galaxy Type 3.

Those harnessing a whole universe as hobby project Type 4.

and type 5 appearing to us as cats just because if I was a Type 5 being that's what I would do.

And all this time I've been telling people He snapped His finger!

Then we must be at the center of the universe.

Or, could it be that we are just at the center of our universe?

IF everything is moving away from the origin of the Big Bang, and we just happened to be in the middle of the pack somewhere, and with the universe expanding faster, then the galaxies behind us would be moving slower than the Milky Way, and the ones out front moving away even faster, all red-shifted (unless you find one moving toward our galaxy (Andromeda)). That does not make us the center of the universe, or of our universe. It just makes us part of the universe, no more, no less.

You've inadvertently made a common ambiguity in your comment on the Big Bang. The Big Bang origin is a theoretical point in spacetime when space did not exist. Thus one cannot put the origin at any location.

My 2 BB's are rolling around in my boxcar, trying with all their might to wrap around that concept. I think I should go into some other avocation, perhaps sweeping the church grounds. (I feel extra tired today, probably the accumulation of weeks without a day off).

In an expanding universe almost everything would appear to be moving away from us (and from each other).

Comets move toward and away from ''us''. At what dimension is the ''us'' part of everything ''appearing'' to move away from ''us''? And is all of this movement a linear vector or some assortment of 3D spirally curved vectors that make it impossible (except with the super computer in the sky) to intrapolate, with respect to all these moving objects, where all of this movement originated (i. e., the geometric center of the ''universe'')?

You just had to go and make my head hurt worse, didn't you?

These motions are no where near rectilinear motions, however in the infinitesimal limit of dt where dt-->0, the calculus is not as challenging.

Given that, there is no actual fixed point of reference on the earth that is not moving in a 24 hour period (unless you count the poles). Other places just have to come back around the next night to see what you are talking about, be it a comet, a planet, the moon, a star, or a whole cluster of galaxies. In the limit, that comet is moving on a near straight line, but the line keeps changing its vector. If the comet is moving toward, then there could be blue shifted lines, if away, then its red-shifted lines in the spectrum. The whole entire spectrum moves, but the lines are the only markers we have to go by.

This might ease your headache. A little 'light' entertainment.

Superman was booked for jumping a red light.

He said he was in a hurry to a rescue and the light was not red - it was green when he passed it.

So they booked him for speeding instead....

So Superman was going so fast, he blue-shifted it from his frame of reference. Nice.

You cannot discern an object moving away from us from us moving away from an object. Moving is moving. Red shift is a red shift. So in an expanding universe we are not necessarily at the center. (this idea goes back to the Middle Ages doesn't it? I believe people were persecuted for not believing this.) Everything is moving outward from a center and no matter where you are in the mass of moving objects, all appear to be moving away from us.

If the size of the universe is infinite, everyone is at the centre.

Interesting way to put it.

This is exactly the task of the James Webb Space telescope. Unlike the Hubble telescope, this incredible piece of engineering is optimized for imaging infrared light instead of visible light. This will allow it to then image "familiar" visible light that is so old it has red shifted deep into the infrared spectrum. This space telescope will be placed at the LaGrangian point L2 for a variety of reasons. The pink part of the image is a solar shield to block the infrared light from the sun.

Now, sirs, THAT is engineering!

The current accepted understanding is that the speed of light in a vacuum is the same regardless of frame of reference.

This means that as long as the light can make it here with sufficient strength for detection, the speed of the source will not inhibit the arrival, only shift the frequency.

If we are talking optical frequencies, the wavelengths we can see with our eyes range from 400 nm to about 700 nm. Pick yourself a spectral line, say sodium D (actually a well-known yellow doublet,

The D1 and D2 lines form the well-known "sodium doublet", the centre wavelength of which (589.29 nm) is given the designation letter "D". (Wikipedia article on sodium D doublet as a Fraunhofer line). You can calculate the frequency of this light easily enough. You can even calculate Doppler shifts based on velocities up to very very near the speed of light. How you apply that knowledge is totally up to you. How fast before the D lines shift to a wavelength above 700 nm? What about a blue spectral line shifting to greater than 700 nm?

Detectors for IR, UV & X-Ray are already out there i.e. Astrosat.

For distant galaxies, using Doppler effect is not truly measuring the speed of distant galaxies but is used to measure the expansion of space.

But is not truly a Doppler effect.

And I understand that to use the term correctly is to use it in a cosmological context.

This is a interesting read,.... at least for a layman like myself.

It depends on the resolution of your red-shift detector.

From what I learned is that stars are not moving, the reason we see stars is because a star is a sun, the thing that is moving is a planet. I was taught this in high school earth science class.

If this information is incorrect, please send an email to my teacher.

Your teacher may have walked off of the edge of the Earth if that was her/his belief.

By the way, he did tell us he was always taking trips while in college.

LDS trips? Trips to the country to watch these non-moving stars? Actually, the only star that does not appear to move in the night sky (and this is due to the rotation of the earth, unless he does not believe in that either) in our hemisphere in Polaris, the North Star, (actually even that star moves ever so slightly, and as our planet precesses its spin this position in the sky changes, making Polaris less true north).

Mind blowing having everything in motion, but remember that the motion is small compared to distances from us to the stars. One star appears to stay in the same relative position to another, or we would have essentially the same constellations as did the Greeks and Egyptians.

"The biggest problem in communication is the illusion that it has taken place."

_G. B. Shaw

Stars were not moving before advanced astronomy took over in the early 20th Century.

Suddenly, they had to pick up speed to catch up on Einstein's theories, the work of Doppler, and a patient fellow named Hubble that studied the spectra of stars using the best American telescope of the time at Mt. Palomar in California. Back before they had to change the name of California.

Please do send this to your teacher in good faith, and tell then by the way, they are all wet.

"dark mass discussion"

So there is going to be a Satanic convention somewhere? Just joking.