The amount of redshift along with the Doppler equation can be used to calculate the velocity of receding galaxies.
Am I missing something??
They use doppler shift to detect planets orbiting distant suns.
Doppler shift is also used in radar, as stated earlier. Difference in velocity really does cause a shift in frequency.
Again, SI units are now based on universal constants. This includes the universal constants that result in the oscillations of a cesium atom. This oscillation will be the same throughout the universe, as much as any other constant is.
Unless, of course, we’ve looked at the behavior of atoms far from earth. Which we’ve done. Is there some set of weird physical behavior that would mimic uniform physical laws and constants throughout the observable universe other than actual uniform physical laws and constants? Maybe so – but the conclusion (not assumption) that we’re measuring actual constants is not arbitrary, and our current definitions are in no way analogous to choosing arbitrary standards.
Yes, quite right – presuming that the redshift is due to the Doppler effect. But, strictly speaking, that is an unevidenced hypothesis.
If those stars are close enough to be able to detect planets, then they are close enough that there is very little cosmological redshift. And, in any case, the detection of planets that way depends only on the variation of redshift, so the cosmological redshift would not affect the measurement.
When used with radar, you have a single clock generating the oscillations (radar signal) and measuring the received timing.
When used with distant galaxies, you do not have a single clock. You are depending on assumptions about the clock rates. This might be a reasonably hypothesis. But it is only an hypothesis. That does not give you any basis to assert that our measurement of time is somehow not dependent on local standards.
We already know that the cesium clock will run at a different speed if in a gravity well.
The cosmos could be such that a distant galaxy appears to be in a gravity well when viewed from here. And it could also be such that we appear to be in a gravity well when observed from that distant galaxy. That would still appear to be consistent with uniform physical laws.
The cosmos could be a stranger place than we take it to be.
So how far out into the universe do we need to go before you are satisfied that the laws of physics are the same? As another example, the movement of stars around the center of galaxies is also measured by doppler shift.
So? The shift in frequency is caused by the movement of the object the radar waves are bouncing off of.
What do clocks have to do with measuring the frequency of light?
If time ticked differently in different frames of reference this would have massive consequences in physical processes. These differences would be seen in how distant stars burn and release energy.
I also stress “frames of reference” here, due to relativity. Clocks on a satellite orbiting Earth will tick at a different rate compared to a clock on Earth due to their placement in Earth’s gravitational well. Clocks do tick at different rates between frames of reference, but not within frames of reference. One confirmation of this fact is time dilation slowing the rate of evolution of type Ia supernovae that are in high redshift galaxies. This again confirms that the redshift is due to velocity because of the expected time dilation.
How would this produce a relationship between distance and redshift?
I have not actually questioned whether they are the same. What I questioned, was your assertion that using the cesium clock amounts to a first principles way of measuring.
Yes. But that measures relative redshift as a way of measuring relative velocities. That is to say, they are relative to the center of the galaxy.
You are repeating yourself.
Yes, motion causes redshift. I have already agreed with that. The unresolved question, is whether all redshift is due to motion. That’s what I see as no more than an untested hypothesis.
You can keep bringing up additional evidence that motion causes redshift. But that does not address the question as to whether all redshift is due to motion.
Everything.
Did you ever discuss that with Albert Einstein?
The frequency of oscillation between these transitions is governed by universal constants.
False. That is relative velocity to us.
An additional test is wavelength dependencies. A doppler shift is wavelength independent, meaning the redshift is the same for all wavelengths. Other processes of redshift, such as absorption and emission in some medium, is wavelength dependent, that is it will redshift some wavelengths more than others.
We also have the slowly evolving type Ia supernovae in strongly redshifted galaxies. Yet another test of the hypothesis.
We also have the correlation between redshift and distance. Yet another piece of evidence for a uniform stretching of spacetime resulting in a redshift.
Then show us.
I will repeat what I said before:
I also stress “frames of reference” here, due to relativity. Clocks on a satellite orbiting Earth will tick at a different rate compared to a clock on Earth due to their placement in Earth’s gravitational well. Clocks do tick at different rates between frames of reference, but not within frames of reference. One confirmation of this fact is time dilation slowing the rate of evolution of type Ia supernovae that are in high redshift galaxies. This again confirms that the redshift is due to velocity because of the expected time dilation.
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So by “first principles” you mean with respect to an abstract mathematical model.
But the discussion was about standards for measuring and describing the real world. It was not about abstract models.
Your post seems to completely miss the point.
Perhaps you are using a very non-standard meaning of “frequency”. The standard meaning is the rate per unit of clock time.
The wikipedia definition: “Frequency is the number of occurrences of a repeating event per unit of time.”
Your earlier statement was about “different frames of reference” which is not at all the same as “within a frame of reference”.
In all honesty, you are turning this into a ridiculous sideshow.
Now that’s topic drift. You can’t get much farther than the edge of the universe.
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What I am saying is that SI units are based on universal constants from physics.
The measurement of light’s frequency doesn’t use a clock:
I meant it to be the same, so my apologies if there was confusion.
Do you agree that SI units are based on universal constants?