Red Shift question(s) and Help

[ccwebb]

Two questions here.

 

The first is about the red shift of light and it came about in another thread called galaxy rotation curve. The answer I understood was, we can determine the rotational speed of galaxies by the red shift of their light. So I went to Google and stated to research red-shift which led me to my question:

 

How do we know that light is red shifted because the light source is moving away from us and not from something else? ie: Gravity has been proven to affect light, couldn't the source be closer and simply shifted red? (Black holes, dark matter...etc)

 

 

Second question, in researching red shift I came across many weird sites that claim they have proof against red shift, big bang, the Twinkie theory and so on... it gave me a headache reading them all and reminded me of traveling salesmen offering cocktails given to cure all ailments! How can someone protect themselves from science lies being wrapped with some truths? As a professional pilot I hear all the time younger pilots using terms incorrectly or distorting them to simply fit the question. How can a non-scientist, who has a fascination about 'Outer Space', not fall for some of the gimmicks out there?

 

Thank you in advance...

[Spyman]

When we are looking at the rotation of a galaxy, we measure the difference of redshift from stars on both sides of it, but from equal distance from its center. Stars on one side are moving away from us and on the other side towards us, which is offset by the average speed of the galaxy itself relative us. As long as the galaxy is not in a collision with another galaxy is should be enough far away from other sources of gravity that stars on both sides are in approximate the same gravity.

[Delta1212]

As far as avoiding junk science: if something is claiming that a scientific consensus is wrong, it's safest to ignore it. That's not to say there aren't plenty of scientists out there banging away at one established theory or another trying to test its limits or prove some aspect of it wrong, but 1: you're much more likely to come across crank sites than you are websites dedicated to these people's research and 2: you should start with a foundation of what we know (or at the very least think we know) before branching off into more speculative areas. Hopefully by the time you've covered the basics in a decent level of depth you'll have a better feel for how the scientific process works and you'll have a better "feel" for who is and is not playing fair with their claims.

 

Also good to remember: most scientists are hesitant to make claims that go against established theory until they've quadruple-checked their results and then had everyone else check them as well. They want to have rock solid evidence before making any major challenges to existing ideas. Those peddling junk science (and science journalists covering actual science who have a tendency to sensationalize) rarely show such restraint.

 

Case in point, when CERN results showed neutrinos traveling slightly faster than light (something that is supposed to be impossible), their response was "Hey guys, we got a weird result. Could somebody check our work and see if we're doing something wrong?" while all the headlines were screaming "Einstein was Wrong!"

 

The former is how an actual scientist sounds. If you read something along the lines of the latter, it's a red flag that whatever you are reading probably wasn't written by an actual scientist.

 

(Incidentally, someone did eventually discover what was wrong at CERN, which is precisely why scientists don't go spouting off about overturning all of physics at the first sign of discrepancy).

[swansont]

When we are looking at the rotation of a galaxy, we measure the difference of redshift from stars on both sides of it, but from equal distance from its center. Stars on one side are moving away from us and on the other side towards us, which is offset by the average speed of the galaxy itself relative us. As long as the galaxy is not in a collision with another galaxy is should be enough far away from other sources of gravity that stars on both sides are in approximate the same gravity.

 

I would think the gravity from the star itself is the larger contribution to gravitational redshift, but I haven't run any numbers to confirm this. or to compare that to the kinematic shifts you might see.

[ccwebb]

Case in point, when CERN results showed neutrinos traveling slightly faster than light (something that is supposed to be impossible), their response was "Hey guys, we got a weird result. Could somebody check our work and see if we're doing something wrong?" while all the headlines were screaming "Einstein was Wrong!"

 

The former is how an actual scientist sounds. If you read something along the lines of the latter, it's a red flag that whatever you are reading probably wasn't written by an actual scientist.

 

(Incidentally, someone did eventually discover what was wrong at CERN, which is precisely why scientists don't go spouting off about overturning all of physics at the first sign of discrepancy).

 

Great point! I remember the news media being in a frenzy but once you started reading the articles... well... the truth came out.

 

When we are looking at the rotation of a galaxy, we measure the difference of redshift from stars on both sides of it, but from equal distance from its center. Stars on one side are moving away from us and on the other side towards us, which is offset by the average speed of the galaxy itself relative us. As long as the galaxy is not in a collision with another galaxy is should be enough far away from other sources of gravity that stars on both sides are in approximate the same gravity.

 

Thank you Spyman, that makes a lot of sense and does a lot to clarify.

 

Now, to play devil's advocate, how do we know that light isn't distorted by dark matter? We've been looking at the stars for a few years now and haven't noticed the gravitational lensing until very recent. (Last year I think?) What about the expansion of space, could that stretch the light into red, yet the actual distance is a lot closer? In the flying world, I teach students that anything between your eyes and an object will make the object appear to be further away. ie: fog, dust, rain, bugs on the windscreen... what if we are simply looking through a lot of 'stuff'?

[Spyman]

I would think the gravity from the star itself is the larger contribution to gravitational redshift, but I haven't run any numbers to confirm this. or to compare that to the kinematic shifts you might see.

Yes, you are correct. The gravitational redshift from the star itself is so small that it's at the limit of detection and for galaxies it's much much smaller. As long as we are not speaking of Black Holes or Neutron Stars and such, the gravitational redshift can be neglected.

 

Thank you Spyman, that makes a lot of sense and does a lot to clarify.

 

Now, to play devil's advocate, how do we know that light isn't distorted by dark matter? We've been looking at the stars for a few years now and haven't noticed the gravitational lensing until very recent. (Last year I think?) What about the expansion of space, could that stretch the light into red, yet the actual distance is a lot closer? In the flying world, I teach students that anything between your eyes and an object will make the object appear to be further away. ie: fog, dust, rain, bugs on the windscreen... what if we are simply looking through a lot of 'stuff'?

A distant galaxy can be considered to be one large spinning disc, as such all effects from space expansion or intervening dark matter should affect the light from both sides of the galaxy approximately equal.

 

The redshift from expansion of space can be much larger for very distant objects than the redshift from rotation, but the redshift from rotation is positive on one side, negative on the other and zero in the middle, so scientists can filter out redshifts from expansion and surroundings to focus on the differences from rotation.

 

If there would be "stuff" obscuring our view then it either covers the whole view of the galaxy and can easily be filtered out or it only covers a part of the view and then astronomers would notice and examine closer why that part are rotating with different speed.

[BearOfNH]

[...]If there would be "stuff" obscuring our view then it either covers the whole view of the galaxy and can easily be filtered out or it only covers a part of the view and then astronomers would notice and examine closer why that part are rotating with different speed.

Not to mention such "stuff" is highly unlikely to crop up in every galaxy under study. One or two, plausible. All of 'em, NFW.

[LaurieAG]

Case in point, when CERN results showed neutrinos traveling slightly faster than light (something that is supposed to be impossible), their response was "Hey guys, we got a weird result. Could somebody check our work and see if we're doing something wrong?" while all the headlines were screaming "Einstein was Wrong!"

 

The former is how an actual scientist sounds. If you read something along the lines of the latter, it's a red flag that whatever you are reading probably wasn't written by an actual scientist.

 

(Incidentally, someone did eventually discover what was wrong at CERN, which is precisely why scientists don't go spouting off about overturning all of physics at the first sign of discrepancy).

 

I never thought that any of the multitude of dedicated physicists, engineers and technicians involved with the project had made any real error so I looked at the paper to see where an error of the magnitude of the discrepancy could possibly slip through during the entire process. I thought that the way the error rates in the calibration were broken down was unusual and could mask a cumulative packet/basket count error over the whole calibration cycle which could equal the main error. With high speed electronics you trigger the packet counter when the start of the packet arrives and increment the counter as when each new packet arrives. The only problem with using this method is if you fail to realise that the count that results from the end of the last calibration packet is one greater than the actual number of packets received. All I know is that they released the recalibration figures with much smaller packet sizes and the errors were exactly the same as for the original calibration figures, just before they found the 'loose wire'.

[ccwebb]

Not to mention such "stuff" is highly unlikely to crop up in every galaxy under study. One or two, plausible. All of 'em, NFW.

 

Not to be a wet blanket, or maybe I am not understanding here... but NFW? I can think of the asteroid belt between earth and mars, the Oort cloud and the milky way that would be in almost every picture? Or am I missing something?

[Spyman]

Not to be a wet blanket, or maybe I am not understanding here... but NFW? I can think of the asteroid belt between earth and mars, the Oort cloud and the milky way that would be in almost every picture? Or am I missing something?

For starters, most asteroids within the asteroid belt orbits close the the plane of the solar system, so we can see distant galaxies without looking through it. The Sun is located far out from the center of the Milky Way so we can notice any difference if we look at distant galaxies through the bulk of the Milky Way or away from it. The Oort cloud could possibly cause a symmetric obscuring over our whole view, but it would also be symmetric over the measurement of galaxy rotation and can thus easily be filtered out.

 

But maybe I misunderstood you and you want to know about cosmological redshift and not the doppler redshift from galaxy rotation?

 

In post #5 you said:

In the flying world, I teach students that anything between your eyes and an object will make the object appear to be further away. ie: fog, dust, rain, bugs on the windscreen... what if we are simply looking through a lot of 'stuff'?

Astronomers can measure the scattering of light from "stuff" obscuring our view and have ruled out effects such as Tired Light:

 

Tired light is a class of hypothetical redshift mechanisms that was proposed as an alternative explanation for the redshift-distance relationship. These models have been proposed as alternatives to the metric expansion of space of which the Big Bang and the Steady State cosmologies are the most famous examples. The concept was first proposed in 1929 by Fritz Zwicky, who suggested that if photons lost energy over time through collisions with other particles in a regular way, the more distant objects would appear redder than more nearby ones. Zwicky himself acknowledged that any sort of scattering of light would blur the images of distant objects more than what is seen. Additionally, the surface brightness of galaxies evolving with time, time dilation of cosmological sources, and a thermal spectrum of the cosmic microwave background have been observed - these effects that should not be present if the cosmological redshift was due to any tired light scattering mechanism. Despite periodic re-examination of the concept, tired light has not been supported by observational tests and has lately been consigned to consideration only in the fringes of astrophysics.

http://en.wikipedia.org/wiki/Tired_light

[BearOfNH]

[...]The Oort cloud could possibly cause a symmetric obscuring over our whole view, but it would also be symmetric over the measurement of galaxy rotation and can thus easily be filtered out.[...]

 

There have been a large number of studies of galaxies and I have yet to read one where the authors mention difficulties stemming from Oort cloud interference. They say the OC is heavily populated, but apparently the density is low enough not to cause problems.

[Spyman]

There have been a large number of studies of galaxies and I have yet to read one where the authors mention difficulties stemming from Oort cloud interference. They say the OC is heavily populated, but apparently the density is low enough not to cause problems.

Yes, you are correct, sorry if I was unclear. What I ment is that it was the only one of the suggested examples that could cause symmetric obscuring in every direction we look and even if it did, it would still not change the results of galaxy rotation. It was not my intention to make it sound as it actually does interfere or cause extra redshifts.

[ccwebb]

Spyman and BearofHN... thank you for explaining it so.

 

Spyman, interesting tidbit there of 'Tired Light'. It goes to show that there is so much more to light than what we can see. My own explanation could have answered this for me. Just because it appears different (further or closer) doesn't mean it is. I teach pilots to trust their instruments, and that is exactly what scientist do. Trust their instruments. Thank you.

[Mordred]

Just to add some information, there is 3 major categories of redshift to consider in Cosmology. Doppler shift =motion, gravitational redshift (redshift due to particles falling into or climbing out of a gravity well) and cosmological redshift-whichis due to expansion. Each form of redshift has its own mathematical formula and each must be considered and accounted for