John Conner

Does the expansion of universe effect light?

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Posted (edited)

in long distances (megaparsec level) does the accelerating expansion of the universe affect on light and it's trajectory?

Edited by John Conner

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Posted (edited)
6 minutes ago, John Conner said:

in long distances (megaparsec level) does the accelerating expansion of the universe effect on light and it's trajectory?

Yes...The expansion of the universe affects light and this is observed by the lengthening of the wavelength or shift to the red end of the spectrum, and is known as "cosmological redshift"

The actual trajectory is affected by spacetime curvature or warping by intervening objects.

Edited by beecee

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1 hour ago, beecee said:

Yes...The expansion of the universe affects light and this is observed by the lengthening of the wavelength or shift to the red end of the spectrum, and is known as "cosmological redshift"

And this is one of the main ways we measure the rate of expansion (and how the acceleration was detected)

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Posted (edited)

   Does the expansion of the universe actually affect the wavelength of light or does it simply affect how that wavelength of light appears or is perceived relative to the observer?

   Isn't it similar to the Doppler Effect, in that the sound of a Train, a Siren or a Race Care doesn't actually change as it approaches or recedes, it just appears to change relative to the listener?

Edited by et pet

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Posted (edited)
5 hours ago, et pet said:

   Does the expansion of the universe actually affect the wavelength of light or does it simply affect how that wavelength of light appears or is perceived relative to the observer?

   Isn't it similar to the Doppler Effect, in that the sound of a Train, a Siren or a Race Care doesn't actually change as it approaches or recedes, it just appears to change relative to the listener?

As answered twice previously, yes, the expansion of the universe does affect the wave length of light. What you need to consider is that firstly, all frames of references are as valid as each other, and of course the observed wave length is relative to that frame. And it follows that from the observers aspect on Earth, we certainly see a real cosmological redshift or lengthening of the wave length of the light.

Edited by beecee

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Posted (edited)

Should this be considered?  :  https://www.science.org.au/curious/space-time/how-do-astronomers-know-universe-expanding

   " When looking at the radiation emitted by distant stars or galaxies, scientists see emission spectra ‘shifted’ towards the red end of the electromagnetic spectrum—the observed wavelengths are longer than expected. Something causes the wavelength of the radiation to ‘stretch’. But rather than an actual change in the wavelength, this phenomenon was something similar to the Doppler effect—they only appear stretched relative to the observer. The further away an object is, the greater the shift.

   The Doppler effect

  The noise of a siren or a car speeding past sounds higher in pitch the closer it gets to you and lower as it moves away. This is called the Doppler effect, where waves, in this case sound waves, change in frequency and wavelength as the source moves towards you (higher frequency, shorter wavelength) or away from you (lower frequency, longer wavelength). There is no actual change in sound; the car isn’t making a different noise. It just sounds different due to the car’s movement relative to you. "

   https://www.science.org.au/curious/space-time/how-do-astronomers-know-universe-expanding

Edited by et pet

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7 hours ago, et pet said:

   Does the expansion of the universe actually affect the wavelength of light or does it simply affect how that wavelength of light appears or is perceived relative to the observer?

   Isn't it similar to the Doppler Effect, in that the sound of a Train, a Siren or a Race Care doesn't actually change as it approaches or recedes, it just appears to change relative to the listener?

These are not illusions, and the measurements are relative to the frame in which they are measured. There is no "appear to change." The sound or light frequency is higher for the recipient when the sources are moving toward each other. If you e.g. have an atom with a resonance at a certain frequency, and one atom emits a photon at that frequency toward an atom that is moving fast enough to Doppler shift the photon out of resonance, that identical atom will fail to absorb it. The light is at a different frequency, and that's all that matters.

44 minutes ago, et pet said:

Should this be considered?  :  https://www.science.org.au/curious/space-time/how-do-astronomers-know-universe-expanding

   " When looking at the radiation emitted by distant stars or galaxies, scientists see emission spectra ‘shifted’ towards the red end of the electromagnetic spectrum—the observed wavelengths are longer than expected. Something causes the wavelength of the radiation to ‘stretch’. But rather than an actual change in the wavelength, this phenomenon was something similar to the Doppler effect—they only appear stretched relative to the observer. The further away an object is, the greater the shift.

This is what was previously described.

44 minutes ago, et pet said:

   The Doppler effect

  The noise of a siren or a car speeding past sounds higher in pitch the closer it gets to you and lower as it moves away. This is called the Doppler effect, where waves, in this case sound waves, change in frequency and wavelength as the source moves towards you (higher frequency, shorter wavelength) or away from you (lower frequency, longer wavelength). There is no actual change in sound; the car isn’t making a different noise. It just sounds different due to the car’s movement relative to you. "

   https://www.science.org.au/curious/space-time/how-do-astronomers-know-universe-expanding

This is poorly worded. There is a change in sound. The car isn't making a different sound, but the sound is different for you.

There is no "absolute" (or "real") sound frequency. It's a relative measurement.

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9 hours ago, et pet said:

Does the expansion of the universe actually affect the wavelength of light or does it simply affect how that wavelength of light appears or is perceived relative to the observer?

Is there a difference?

How would you distinguish between the “actual wavelength” and the wavelength measured by an observer? 

All the related properties (length, time, energy) are observer dependent so multiple observers could measure different wavelengths.

You can choose to define the “real” frequency as that measured in the frame of reference of the source, but that is just a convention and doesn’t affect what is actually perceived by the observer. 

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8 hours ago, et pet said:

Should this be considered?  :  

Certainly not in the vane in which you seem to be applying meaning to. The fact remains that all frames are as valid and real as each other. The measurement taken [as Strange has said] is observer dependent and GR tells us that there is no preferred frame. That is the crux of the matter. 

 

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Okay thanks guys. another question. what about observing an accelerating body but in all dimensions? an acceleration in all directions simultaneously but for moving body with force. how do we see that?

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22 minutes ago, John Conner said:

Okay thanks guys. another question. what about observing an accelerating body but in all dimensions? an acceleration in all directions simultaneously but for moving body with force. how do we see that?

It sounds like the body has just exploded.

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7 minutes ago, Strange said:

It sounds like the body has just exploded.

well. we're considering... i'm just asking. how do we see it?

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5 minutes ago, John Conner said:

well. we're considering... i'm just asking. how do we see it?

It is not clear what you are asking?

How do we see an object explode? Or how do we see the expansion of the universe? (Which is not an explosion, and there are no forces involved.) Or how do we detect that the expansion started accelerating?

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A body can only accelerate in one direction. It’s a vector. 

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Posted (edited)
1 hour ago, swansont said:

A body can only accelerate in one direction. It’s a vector. 

that's exactly what i'm asking. let's consider a body that is accelerating simultaneously in all directions, and for now this is hypothetical but how do we see it?

 

4 hours ago, Strange said:

It is not clear what you are asking?

How do we see an object explode? Or how do we see the expansion of the universe? (Which is not an explosion, and there are no forces involved.) Or how do we detect that the expansion started accelerating?

i mean observing. like we examine sth in relativity. when a hypothetical body does such motion, does the observation change since it's accelerating? observations are relevant in respect to frames. since body's frame is accelerating it should change but how? (and yes my english is a little rusty... sorry)

Edited by John Conner

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2 minutes ago, John Conner said:

that's exactly what i'm asking. let's consider a body that is accelerating simultaneously in all directions, and for now this is hypothetical but how do we see it?

It can’t be exactly what you’re asking, since I just said you can only accelerate in one direction.

What you are asking us to consider is impossible.

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2 minutes ago, swansont said:

It can’t be exactly what you’re asking, since I just said you can only accelerate in one direction.

What you are asking us to consider is impossible.

nothing's impossible for imagining. does the black body exist? this is just idealized body like black body. if there was a body that could do that but not the metric itself what would have happened?

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10 minutes ago, John Conner said:

that's exactly what i'm asking. let's consider a body that is accelerating simultaneously in all directions, and for now this is hypothetical but how do we see it?

The only way something can "accelerate in all dimensions" is if it undergoes rapid spontaneous disassembly (ie. it explodes). I'm guessing you have seen things explode? Or fireworks, maybe?

This has absolutely nothing to do with the topic of the thread, so I don't know why you are asking.

 

12 minutes ago, John Conner said:

i mean observing. like we examine sth in relativity. when a hypothetical body does such motion, does the observation change since it's accelerating? observations are relevant in respect to frames. since body's frame is accelerating it should change but how?

As the motion you are describing is not possible, observations are irrelevant.

3 minutes ago, John Conner said:

nothing's impossible for imagining.

If you can imagine something moving in all directions at the same time, then you can answer the question.

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Posted (edited)
52 minutes ago, John Conner said:

nothing's impossible for imagining.

Imagining has little to do with reality. I can imagine being the greatest physicist ever to exist. Reality says otherwise.

 It's good to have imagination in problem solving but to be effective must be backed up by reality. 

Edited by Mordred

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57 minutes ago, John Conner said:

nothing's impossible for imagining. does the black body exist? this is just idealized body like black body. if there was a body that could do that but not the metric itself what would have happened?

No, it’s not. It’s a contradiction of the concept of a vector. A vector points in one direction. This is not optional.

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14 hours ago, swansont said:

No, it’s not. It’s a contradiction of the concept of a vector. A vector points in one direction. This is not optional.

It can't be described by a single vector. If the body was expanding away from some central point (and say, each point proportionally to the distance from that point) the vector concept can help describe it. Each vector would point in one direction.

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1 hour ago, J.C.MacSwell said:

It can't be described by a single vector. If the body was expanding away from some central point (and say, each point proportionally to the distance from that point) the vector concept can help describe it. Each vector would point in one direction.

It's a body. How does a body accelerate in more than one direction?

John Conner has been given several chances to clarify if he means an explosion (which becomes multiple bodies) or an expanding body, and has tenaciously refused to confirm this, so I am answering under the default assumption of a rigid body.

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42 minutes ago, swansont said:

It's a body. How does a body accelerate in more than one direction?

John Conner has been given several chances to clarify if he means an explosion (which becomes multiple bodies) or an expanding body, and has tenaciously refused to confirm this, so I am answering under the default assumption of a rigid body.

I guess the assumption would be that it isn't a rigid body.

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8 minutes ago, J.C.MacSwell said:

I guess the assumption would be that it isn't a rigid body.

Maybe a balloon?

But it is obvious how we can observe a balloon, so I don't really know what the question is.

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Hello

consider a body that is accelerating in space-time. and the length of the body is extremely large, for example one megaparsec. now we set the four-acceleration of the body as such that it will be the sum of two four-accelerations which one of them is a four acceleration in the body's length's direction and with the quantity of spacetime expansion rate and the other is a four acceleration that is perpendicular to first four-acceleration's direction and with a quantity large enough to be effective in relativity. now from a stationary observer point of view (don't be clingy, if you don't like it pick any inertial observer) how will it be observed?

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