Speed of light/electromagnetic waves is constant?

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Discussion Overview

The discussion revolves around the constancy of the speed of light and the implications of redshift in the context of an expanding universe. Participants explore the relationship between the wavelength of light from distant galaxies and its speed, as well as the nature of outer space as a vacuum.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants propose that as galaxies move apart, the wavelengths of light stretch, leading to redshift, but question whether this stretching could cause light to disappear completely.
  • Others clarify that while light does not disappear, its wavelength increases, eventually reaching a point where light from distant galaxies may no longer be visible due to extreme redshift.
  • There is a claim that the speed of light remains constant at 299,792,458 m/s in a vacuum, regardless of the energy of the photon.
  • Some participants challenge the notion that outer space is a perfect vacuum, suggesting that the conditions of expanding space may affect the speed of light.
  • Others argue that outer space is sufficiently close to a vacuum for the speed of light to be considered constant in practical terms.

Areas of Agreement / Disagreement

Participants express disagreement regarding the nature of outer space as a vacuum and its implications for the speed of light. There is no consensus on whether the conditions of expanding space affect the constancy of light's speed.

Contextual Notes

Participants reference classical laws of light speed in vacuum versus denser mediums, and the discussion includes assumptions about the nature of cosmic expansion and the density of the universe over time.

Yash1993
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Since Edwin Hubble proposed distant galaxies move apart from each other as spectra of each galaxy is shifted towards the red end. this created the law that universe is expanding exponentially since big bang. and these galaxies spectra are due to stretching of wavelength of light incident from moving apart galaxies. Stretching more wavelengths of light could been light disappears completely? Although, photons acquire their energy and speed in universe. till its wavelength have affected so does it speed too?
 
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Hello Yash, :welcome:

Yash1993 said:
Stretching more wavelengths of light could been light disappears completely
No, it doesn't disappear. But the wavelength gets longer and longer the further you look. Until you see the 'light' from the big bang -- when the wavelength is in the microwave range. The so called cosmic microwave background. Very interesting subject.

Speed stays the same: 299792458 m / s exactly.
 
BvU said:
No, it doesn't disappear. But the wavelength gets longer and longer the further you look.
It will eventually, though! After about a trillion years, redshifts will be to the point that no galaxies outside the local cluster will be visible as the wavelengths of their light will have redshifted to be longer than the cosmological horizon.

Of course, the Earth will be long gone by then.

Yash1993 said:
this created the law that universe is expanding exponentially since big bang.
Not really. The expansion has changed over time as the density of the universe has changed. Only in the special case where the density is constant is there exponential expansion (which may be the case in the far future, if the cosmological constant is non-zero).
 
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Yash1993 said:
Although, photons acquire their energy and speed in universe. till its wavelength have affected so does it speed too?

It does not. A photon of any energy travels at c in a vacuum.
 
Drakkith said:
It does not. A photon of any energy travels at c in a vacuum.

Outer space isn't vacuum! so? Although classical law stated that speed of light is constant in vacuum, going to lesser in denser medium and zero in superatomic field. Condition of ideal vacuum is not satisfied by expanding space between galaxies!
 
Yash1993 said:
Outer space isn't vacuum! so?

Of course it is.
 
Yash1993 said:
Outer space isn't vacuum! so? Although classical law stated that speed of light is constant in vacuum, going to lesser in denser medium and zero in superatomic field. Condition of ideal vacuum is not satisfied by expanding space between galaxies!
It's close enough that it doesn't really matter.
 

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