# What is Blue shift: Definition and 26 Discussions

A blueshift is any decrease in wavelength (increase in energy), with a corresponding increase in frequency, of an electromagnetic wave; the opposite effect is referred to as redshift. In visible light, this shifts the color from the red end of the spectrum to the blue end.

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1. ### B Conflict Between Time Dilation and Red/Blue Shift?

Experiment 1: Astronaut travels away from Earth at near the speed of light, then travels toward the Earth at near the speed of light. Einstein tells us she barely aged, but red shift/blue shift don't seem to agree with that. While traveling away, both Earth and astronaut observe each other...
2. ### I Red shift / Blue Shift - Gravity Well Roundtrip

If I shine a white light out into space from Earth, and it bends around a black hole and comes straight back to me so I can see it in my telescope, is the light red or blue shifted, or neither? For sake of the thought experiment, let’s leave out cosmic expansion that would stretch it on it’s...
3. ### B Is blue shift as common as red shift?

A somewhat trivial question, but I hear of redshift a lot more than blue. And is possible to get a list of galaxies that display these attributes? I would like to use the data for a project. Thanks guys.
4. ### B Photon red shifting and Doppler effect

When thinking of sound waves (or more commonly seen waves) the doppler effect is fairly obvious. A car is moving away from you, it's horn's membrane is fluctuating, increasing & reducing air pressure over time. So if it's moving away from you the sound's peak would occur further away...
5. ### A Effect of Blue-Shifted GWs on Particles

I assume that the energy transported by a gravitational wave is dependent on its frequency, just like EM waves. If that is the case, let's imagine a particle traveling at relativistic speeds relative to the lab frame. Let's imagine the interaction of this relativistic particle with a...
6. ### Red Shift & Blue Shift: Explained

I apologize if this is a dumb question, or if I am not remembering things correctly, but ... ... wasn't one of the earliert objects (a Cepheid?) Hubble detected as red-shifted located within the Andromeda Galaxy? If so, and since we're on a "collision course" with the Andromeda, why didn't...
7. ### Mass Increase and Distances: Red Shift or Blue Shift?

In a hypothetical universe where mass of matter constantly increases, will we observe that distances also constantly increase? This is not a new theory, I'm just asking what classic GM says about that. If we are in a galaxy with constantly increasing mass, measuring distances to other...
8. ### Special Relativity and Blue Shift question

Earlier today I was on youtube when I saw this comment I went to respond to this saying that the light would blue shift out of the visible spectrum and you wouldn't be able to see anything. But then I thought about time dilation from relativity and wondered if the slowing down of time would be...
9. ### Why is a Blue Shift in Kruskal Szekeres not Physical

In my intro. to GR class we recently covered the Kruskal Szekeres diagram and trajectories within the diagram. My question comes from a comment made by my professor about time-like trajectories emerging from v=0 and that if an emitter sends a light signal to an observer it will be blue shifted...
10. ### Red shift and blue shift as relating to time dilation

I was listening to a lecture about the expansion of the universe and found myself confused about the light we see from very distant galaxies. These galaxies are red shifted because they are moving away from us and the photons are being stretched. Does this mean that the galaxy will appear to...
11. ### Free fall and blue shift question.

Lets say I am in free-fall towards some massive body and I have 2 mirrors and photons bouncing in between them. Now as I fall closer to the massive body the light should get blue-shifted right? And let's say that the frequency of light that I started with is x. As I fall closer I put a jar of...
12. ### Measuring Frequency of Trans Planckian Blue Shift

Consider a source of radiation that is emitting the radiation at the highest possible frequency inversely proportional to the Planck time interval as measured in the rest frame of the source. What frequency would an an observer that is moving towards the source measure? What frequency would an...
13. ### Black Hole Singularity Blue Shift

Theoretically, would everything be REALLY REALLY blue at the singularity of a black hole because of the blue shift caused by all the light racing to it (the singularity)? Arigato, -llama
14. ### What is the mathematical explanation behind red/blue shift caused by gravity?

Can anyone supply me with the mathematics behind the energy gain/ loss as a photon travels through a gravitational potential difference?
15. ### Blue shift galaxies and the expanding universe

We are told the universe is expanding because galaxies are red shifted and that it is a doppler effect. Do blue shifted galaxies contradict the idea of an expanding universe?
16. ### Is blue shift a potential problem for near light speed travel?

I've heard that future spaceships traveling at near the speed of light will have to deal with massive amounts of radiation due to interstellar gas. I think these spaceships might also have to deal with radiation from star light being blue shifted. How close to the speed of light would one have...
17. ### Measuring the Accuracy of EM Spectrum Shift: Red vs Blue

How accurate is it possible to measure the EM spectre ?
18. ### Red or Blue Shift: Moving Light Sources Forward/Backward

I want to know if the red or blue shift apply if I am moving away or toward a light beam and if it still apply if I am moving the light beam source with me forward or backward.
19. ### Red Shift and Blue Shift: Is It Possible?

I was thinking today and had an idea but didn't know if it was possible. When an object moves toward or away from an observer, the light (such as visible light) "shifts", the wavelengths become closer together (moving toward you) or further apart (moving away from you). Say for example we...
20. ### Can gravitational blue shift happen without gravitational time dilation?

First, a simple scenario to set our expectations: Consider a "stationary" massless non-relativistic test particle in empty space. We'll call the particle "P". At a very large proper distance to the cosmological "west" of P there is a neutron star, at proper rest relative to P. Let's call...
21. ### Quick easy clarification (redshift vs blue shift)

i just have the two mixed up, and need an example to set it straight... lets say you're source is a red light (hight wavelength, low frequency) to green light (lower wavelenght, higher frequency)... that would be a blue shift? redshift = wavelength (H->L) frequency (L->H)...
22. ### Blue Shift objects; is there a list/table?

I know M31 is on the list and I know there aren't a lot of these objects at any distance. Long ago I subscribed to the thought that EM probably fatigues slowly as it propagates through space or any medium for that matter. :-) I would like to see the actual data we have on blue shifted...
23. ### Why do we have red shift and blue shift, and not only one?

I hardly understand anything about relativity (as would be evident from my threads and posts), and thus, this dumb question. If there is only length contraction, and not length expansion, why do we have two shifts, namely redshift and blue shift? should not only there be only blue shift due to...
24. ### Exploring the Doppler Effect: Red Shift, Blue Shift, or Just Curiosity?

This might be a stupid question, but it came to me the other day while reading. Since the speed of light is the same in all frames what would happen if you were chasing a light beam at .999% c, so you were heading right for it (but could never catch it) and it is ahead of you traveling at c. If...
25. ### What is the appropriateness of the term potential in general relativity?

What is the highest known blue shift?
26. ### What Causes Blue and Red Shift in Light?

what exactly is the blue and red shift? what happens? why does this happens?