One of the optical problems with turning light into a beam is the size of the source. In the case of laser diodes this is rather small which allows a fairly decent narrow beam of light to be produced. A LED can't do the same thing and the light isn't coherent.
When said beam hits something it heats up. The degree depend on power. Suppose I am wondering about the mechanism that causes that,
I meant your context in relation to the cosmology we have been discussing lately.
The universe is expanding and it’s accelerating. Star formation peaked between 7 and 9 billion yrs ago. The question Id like to get answered is has the expansion rate changed , or has it been constant?
Just when I thought this Thread can't get Worse. It gets Worse!
OK, 4 ;-) winks from @cumbb is not his record. I recently recorded 5!
The most difficult book I have on loan at the moment is Songs of the Dying Earth:
I have returned it to the Library 2 times. But have taken it out again, which I think is called Masochism. Frankly it destroys my already fragile mind with its Weirdness.
TBH, I find the Feynman Lectures on Physics easier.
I wonder if @cumbb is related to Mazirian the Magician:
https://en.wikipedia.org/wiki/Jack_Vance
Some entities are best avoided. I think @cumbb should be sectioned for a VERY LONG TIME. It might be a kindness. 😉
There is no absolute certainty that the expansion of the universe is accelerating.
Some physicists claim that the original evidence for accelerated expansion is, at most, 3-sigma.
This is far short of the 5-sigma standard required to claim a discovery of fundamental significance.
There is a problem with the current size of the database, but that is getting larger as physicists work on the problem.
Getting through those 22 stories written in honour of Jack Vance would certainly be a mind-bending marathon!
https://en.wikipedia.org/wiki/Songs_of_the_Dying_Earth
I was a big fan of Jack Vance during the science fantasy period of my life.
Servants of the Wankh from the Planet of Adventure series - what fun!
https://en.wikipedia.org/wiki/Planet_of_Adventure
For crying in a bucket Galu, one minute we are trying to delve into the deepest mysteries of the cosmos, which you just dismissed with that 3-sigma jibe, and the next post you’re putting up pictures of white turds and insect-birds.
I suspect heat will be generated if atoms or molecules are energised enough to re-radiate incident EM radiation in the infra-red region. Interesting thought though is what happens when you shine an IR lamp on your skin. Clearly your skin cells are re-radiating at IR so that’s why you feel warm. Or is it because molecules and/or atoms are just jiggling about, to use Feynman’s favourite expression?
Or maybe in a lasers case bombarded with massless wavelike particles. In any case lasers like light sales are instances where light produces energy. IR lamps are more like electric fires. A laser - doesn't seem to matter what the wavelength is.
Conventional lasers are a little like true light clocks base on transit time. Gavity changes wavelength but also changes time, In a lasers case frequency matters.
@Bonsai
I could only comment on your initial statement because I did not fully understand the premise behind your subsequent question.
Einstein's field equations permit three possible scenarios for the rate of expansion of the universe, based on the assumption of its isotropy.
An accelerating expansion is not one of those three scenarios, but requires a positive value of the gravitational constant, AKA dark energy. It is now postulated that at some point in its history the universe started to expand at an increasing rate (5 billion years ago according to Wiki).
Did you think that this point coincided with the peak in star formation that you mentioned?
I could only comment on your initial statement because I did not fully understand the premise behind your subsequent question.
Einstein's field equations permit three possible scenarios for the rate of expansion of the universe, based on the assumption of its isotropy.
An accelerating expansion is not one of those three scenarios, but requires a positive value of the gravitational constant, AKA dark energy. It is now postulated that at some point in its history the universe started to expand at an increasing rate (5 billion years ago according to Wiki).
Did you think that this point coincided with the peak in star formation that you mentioned?
Galu, IIUC, peak star formation occurred between 7 and 9 billion yrs ago, but quite how this might feed into an accelerated expansion starting at 5 billion yrs ago I haven’t worked out. You have an expanding universe (so time is ’stretching’ anyway) and further, would there be a delay due to the timescales involved before it contributed to observed accelerated expansion? I don’t know.
Bonsai, you have no idea what you are talking about.
Watch this video about "Firefly" if you please.
As an Autistic person, I naturally admired "River".
Unfortunately I was also drawn to Saffron.
Bit of a looker, you might agree. We all make mistakes. Kaylee would have been a better choice, but that is hindsight. 🙂
Watch this video about "Firefly" if you please.
As an Autistic person, I naturally admired "River".
Unfortunately I was also drawn to Saffron.
Bit of a looker, you might agree. We all make mistakes. Kaylee would have been a better choice, but that is hindsight. 🙂
It all seems to be based on distant s1a supernovas. Standard candles. I'd like to know how they obtain a sigma for any variations in their brightness. One attempt - it leaves me wondering what the paper means
https://www.aanda.org/articles/aa/full_html/2018/07/aa31425-17/aa31425-17.html
It's a long and involved paper, but it implies that our current database is neither dependable or large enough for us to be absolutely certain of the accelerating rate of expansion of the universe.
It seemed to also suggest additional parameters are needed to tie it all down.
😉 My wife has been told to go gluten free so trying bake some gluten free bread.
I mention a place with and without a black hole and stars buzzing around. It's resurfaced in connection with a rather odd object.
https://en.wikipedia.org/wiki/Omega_Centauri
😉 My wife has been told to go gluten free so trying bake some gluten free bread.
I mention a place with and without a black hole and stars buzzing around. It's resurfaced in connection with a rather odd object.
https://en.wikipedia.org/wiki/Omega_Centauri
I can provide more information on how the two events relate in time.
Accelerating expansion is said to have begun when the universe entered its dark-energy-dominated era.
This era was proceeded by the matter-dominated era.
Peak star formation occurred towards the end of the latter era, as shown in the attachment.
Attachments
Data which supports accelerating expansion is also obtained by examining the growth of large scale structure in the universe, measurements of the cosmic microwave background, gravitational lensing and baryonic acoustic oscillations (see link below).
https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations