Dear Dr Joe Pesce,
Appreciate your commitment to answer questions at this forum and your willingness to put your expertise at our service! That being said, I find some aspects of your answer to me (#120 in this thread) are confusing. Your explanation that light from the most distant galaxy was originally ultraviolet but that by the time it reached us, because of the expansion of the Universe, it had red-shifted into the microwave and infra-red range, while it might hold good for that particular Galaxy does not seem to hold good for others. For instance, the Galex observatory that was in operation from 2003 to 2010 operated solely in the ultra-violet range, yet was able to map stars and galaxies that were 10 billion light years distant. (Hopefully, the James Webb Telescope will be able to do even better.) The significant point is that these observations were made in the ultraviolet range, not ultraviolet that had morphed into the infrared or microwave frequencies. Surely, if the Universe were expanding, it would do so at a uniform rate? Not haphazardly. If the Universe were indeed expanding at the rates being widely proclaimed then it should be impossible to see in the ultraviolet to distances of billions of light years.
Would it be possible to ascertain how these two conflicting theories are being so widely published and what is the reasoning behind such divergent facts?
Jzz, thanks again for allowing me to clarify this important aspect of astrophysics.
The expansion isn’t happening for just some objects, nor is the shifted wavelengths only happening for a subset of objects: the expansion is universal (everywhere) and every object emitting electromagnetic radiation is affected in the same way (different amounts for different distances traveled, of course).
For all objects emitting ultraviolet radiation (say) 13 billion years ago, ALL of those ultraviolet photons have lost energy and are now emitting in the millimeter part of the electromagnetic spectrum, after traveling to us (13 billion light years from the source), or any other location 13 billion light years from the source.
You mention Galex observations of distant objects in the ultraviolet. Galex is observing those ultraviolet photos today. At the source (say at 10-12 billion light years away) those photons were emitted at hard x-rays or gamma-rays. In traveling through the expanding universe (see my response to your previous question), their wavelengths have been stretched (because space is being stretched from under them), lowering their energy (longer wavelengths means lower energy) and are now in the ultraviolet.
So whenever we observe an object today, in whatever region of the electromagnetic spectrum, if we want to know what those photons were at the source, we need to “correct” for the distance traveled.
I’ll make up an example, as a thought experiment: Our Sun emits electromagnetic radiation from the radio to the gamma-rays. If I magically place the Sun at 10 billion light years away, and then step back and observe the Sun, I am seeing those photos as they have been redshifted by their long journey (through an expanding universe). The radio and infrared photons are redshift almost to zero energy (at least to very long wavelength radio). The higher energy photons, say from visible to gamma-ray at the point they left the Sun, would be observed here on Earth from radio (for the source visible-light photons) to visible (for the source gamma-ray photons).
In my example to your previous question in this thread, for the most distant galaxy. ALMA is observing, specifically, a spectral line created by oxygen in the ultraviolet portion of the spectrum (at the source). That spectral line has been redshifted into ALMA’s viewing window in the millimeter part of the spectrum. It’s that spectral line that allows us to measure the distance. There are photons throughout the electromagnetic spectrum emitted by the source that are all redshifted. Some out of ALMA’s range, and some in it – depending on their initial wavelengths.
I hope this makes sense.