Red shift | Scale of the universe | Cosmology & Astronomy | Khan Academy
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Comments
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I am confused and not convinced by the explanation.
I am imagining a case where a single (first) photon emitted just after the source started moving away at the 1/2 speed of light and then the source stops. Will we still see the red shift in this case ? In this case the photon was emitted at a given point in time at a particular frequency why would then its wavelength change ? (because now the source is no longer moving)
Does it have anything to do with the change in wavelength of the photon during the process of emission ? The reason I say this is - given the fact that the source is moving away and the process of emission of the photon takes some quantum of time, the source takes delta-t seconds to emit the photon and in that time the source would have moved by a distance delta-d causing the the photon that is being emitted to stretch a bit (during the process of emission) ending up with a larger wavelength ?
Am I sounding dumb ? -
I'm no expert, but i think the author should differentiate between redshift observation and the explanation for redshit. If i remember correctly, redshift is the difference between the observed hydrogen spectum here on Earth, and the measured hydrogen spectum of a distant star ?
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how do we know form observation that is really a red shift ... or is just a red star???
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doppler effect ??
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How do you know what the frequency would be if the source was not moving to conclude the light is redshifted?
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Perceived wavelength? if the reason for redshift is that the source travelling away from the observer "stretches" the wave, would that not mean that the photon speeds up? how else would it compensate for the distance? if it is only "perceived" the why would there be redshift?
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while i understand that this is the commonly held belief, it does begin too look like we may have some of this wrong. Why is it that we believe that a light source travelling at a significant fraction of light speed will not have any ability to modify the speed of it's emitted light? after all, there are no other cases for such behaviour, so why would we theorize something so unreasonable about light?
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so if the speed of light was constant despite the medium, then why does refraction occur? i am confused
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Confusing!!
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I do Kahn
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Cool laws! But if an object is not moving closer or farther away but is orbiting you are moving sideways, will the waves emit a yellow color?
Thanks anyway! -
Thank u!
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How would you know if its moving away from you or if your moving away from it, if it looks the same as the stationary one?
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The photons (((E=hf))) only exist now are in fact a rings series of inward spherical sine wavefronts coming into +1=0 now -1 out of existence therefore the waves move but the (liquid or plasma) photons coming into +1=0 now -1 out of existence do not move!!
We have the Doppler shift because the positive surface of a negative expanding light sphere forms input +1=0 now -1 output wave chain reactions from A to B.. . .The greater the positive 4pi energy compression contracting space time +1=0 now -1 the shorter the expanding 2pi spiral wavelengths.. . .
The magnetic fields (Amplitude) is always at right angles to the direction of the electric 2pi spiral current.. . .Huygens wavelets are a rings series of inward 4pi spherical sine wavefronts coming into every point transverses photon energy oscillating the total amplitude of sinusoidal wavefronts are rather like the bit's, or zeros and ones of a computer screen, with the Planck's constant h the moment of action continuously forming a blank canvas that we can interact with turning the possible into the actual.. . .
And because the positive surface of a negative expanding light sphere forms input +1=0 now -1 output wave chain reactions from A to B.. . .This is the reason for entanglement because the positive surface of a negative expanding light sphere is entangling +1=0 now -1 unfolding wave chain reactions from A to B.. . .
The only difference between a Positron +1=0 now -1 electron Wave Centre made of vibrating wavefronts concentrically layered like an onion!!.. . .And the Two dipole energy states of a Photon is time dilating Volume!!
In the future when there is a locational 4pi spherical inward absorption +1=0 now -1 outward emission of quantized spherical wavefronts of electromagnetic radiation the photons polarization between the crests and troughs will remain the same sharing the same expanding moment of time no matter how larger they become until acted upon by an external force.. . .
And because blue light has greater 4pi positive energy compressing the wave amplitude +1=0 now -1 the shorter the expanding 2pi spiral wavelengths.. . .Therefore the greater the photon energy the larger the oscillating wave amplitude +1=0 now -1 the spiral radians (Shorter spiral wavelengths have a larger Volume area) thus scatter more than red light because red light photon energy the smaller the oscillating wave amplitude +1=0 now -1 the spiral radians (Longer spiral wavelengths have a smaller Volume area) thus longer wavelengths that can penetrate straight through gases, dust and interference from other sources.. . .
Therefore because blue light photons transverse Input +1=0 now -1 output within a larger but shorter spiral wavelength they are simply lagging behind red light photons over many light years from A to B.. . .Because red light photons transverse the Cosmos within smaller longer spiral wavelengths simply are more direct having their own unique position and momentum in space and time."
Therefore the big bung theory is busted.. . .LOL!!!
Everything is formed by a locational 4pi spherical inward absorption +1=0 now -1 outward emission of electromagnetic waves.. . .All motion is 2pi spiral.. . .And all direction is 4pi spherically curved." -
The finished diagram (around the 5:00 mark) is confusing as it actually shows the positions of the objects at sometime in the future; i.e. when the moving light source is further away from the observer. A more accurate representation should show the moving star at the same distance from the observer.
At this exact instant in time, when both objects are equidistant from the observer, and taking into account that the speed of light has to remain constant, the light emitted at that instant will reach the observer at the same time from both sources. Surely, at this instant in time, and if both objects are emitting the same frequency of light,the using λ = v/f shouldn't the wavelength remain the same? Hence the observer shouldn't see any red shift?
I know I'm missing something here, any help would be appreciated :) -
What program are you using???
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Khan Academy, I love all your videos, They explain things very very well, especially for someone who wants to learn things his teacher won't bother teaching. However, in this instance, I'm confused. Why exactly was the wavelength stretched? I undersand how it moves half-the distance away in the time it takes for the light to reach your eye, but then, why does light still have to maintain the same number of waves/cycles? Because this is the fundamental point, at least in my interpretation, that means each wavelength must be stretched. i just don't get why it has to satisfy the same number of cycles each time...
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For and alternative view, see my video Shifting Blue. :)
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So red shifting can cause light emitting objects to become invisible
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Great stuff! I love to review the simple stuff a lot, it seems to help.
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