Ask Science
Ask a science question, get a science answer.
Community Rules
Rule 1: Be respectful and inclusive.
Treat others with respect, and maintain a positive atmosphere.
Rule 2: No harassment, hate speech, bigotry, or trolling.
Avoid any form of harassment, hate speech, bigotry, or offensive behavior.
Rule 3: Engage in constructive discussions.
Contribute to meaningful and constructive discussions that enhance scientific understanding.
Rule 4: No AI-generated answers.
Strictly prohibit the use of AI-generated answers. Providing answers generated by AI systems is not allowed and may result in a ban.
Rule 5: Follow guidelines and moderators' instructions.
Adhere to community guidelines and comply with instructions given by moderators.
Rule 6: Use appropriate language and tone.
Communicate using suitable language and maintain a professional and respectful tone.
Rule 7: Report violations.
Report any violations of the community rules to the moderators for appropriate action.
Rule 8: Foster a continuous learning environment.
Encourage a continuous learning environment where members can share knowledge and engage in scientific discussions.
Rule 9: Source required for answers.
Provide credible sources for answers. Failure to include a source may result in the removal of the answer to ensure information reliability.
By adhering to these rules, we create a welcoming and informative environment where science-related questions receive accurate and credible answers. Thank you for your cooperation in making the Ask Science community a valuable resource for scientific knowledge.
We retain the discretion to modify the rules as we deem necessary.
view the rest of the comments
That's true! There is a kind of incestuous relationship between the cosmic distance measurements and the cosmic model. Astronomers are able to measure parallax only out to 1000 parsecs, and standard candles of type Ia supernovae to a hundred megaparsecs. But the universe is much bigger than that. So as I understand it they end up climbing a kind of cosmic ladder, where they plug the measured distances up to 100 Mpc into the the ΛCDM model to calculate the best fit values for the amounts of matter/dark matter and dark energy. Then they plug in those values along with the redshift into the model to calculate the distances to ever more distant objects like quasars, the Cosmic Microwave Background, or the age of the universe itself. Then they use observations of those distant objects to plug right back into the model and refine it. So those values - 28.6% matter 71.4% dark energy, 69.6 km/s/Mpc Hubble constant, 13.7 billion years age of the universe - are not the result of any single observation, but the combination of all observations taken to date. These values have been fluctuating slightly in my lifetime as ever more detailed and innovative observations have been flowing in.
Are you an astronomer? Maybe you can help me, I've been thinking - how do you even measure the redshift of the CMB? Say we know that CMB is at redshift 1100z and the surface of last scattering is 45.5 GLy comoving distance away. There is no actual way to measure that distance directly, right? Plugging in the redshift into the model calculator is the only way? And how do we know it's 1100? Is there some radioastronomy spectroscopy way to detect elemental spectral lines in the CMB, or is that too difficult?
If we match the CMB to the blackbody radiation spectrum, we can say that its temperature is 2.726K. Then if we assume the temperature of interstellar gas at the moment of recombination was 3000K, we get the 1100z figure. Is that the only way to do it? By using external knowledge of plasma physics to guess at the 3000K value?