APOD: Split the Universe (2017 Apr 01)

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Re: APOD: Split the Universe (2017 Apr 01)

Postby Guest » Mon Apr 17, 2017 1:29 pm

Chris Peterson wrote:Keep in mind that photons are not really massless. They have energy, and therefore a mass equivalent. They also have momentum, which means a mass equivalent. The confusion likely comes from the understanding that a photon has zero rest mass. But that's a theoretical concept, given that a photon is never at rest.

While Art is correct that the kinetic energy of CMB photons is decreasing (because of redshift), this does not violate the law of conservation of energy, because kinetic energy is an observer dependent property- the kinetic energy we measure depends upon our frame of reference.


Can you blame us non scientists for thinking that conservation of energy is a law when scientists commonly call it such? (Just an amusing irony :wink: )

The frame of reference energy dependence is interesting. Would it be correct to then assume that the energy of these CMB photons hasn't really decreased, it's just that they look that way due to the expansion of the universe? Wouldn't that mean that the overall energy of the whole Universe is unchanged due to cooling?

Bruce

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Re: APOD: Split the Universe (2017 Apr 01)

Postby Chris Peterson » Mon Apr 17, 2017 1:38 pm

Guest wrote:
Chris Peterson wrote:Keep in mind that photons are not really massless. They have energy, and therefore a mass equivalent. They also have momentum, which means a mass equivalent. The confusion likely comes from the understanding that a photon has zero rest mass. But that's a theoretical concept, given that a photon is never at rest.

While Art is correct that the kinetic energy of CMB photons is decreasing (because of redshift), this does not violate the law of conservation of energy, because kinetic energy is an observer dependent property- the kinetic energy we measure depends upon our frame of reference.

Can you blame us non scientists for thinking that conservation of energy is a law when scientists commonly call it such? (Just an amusing irony :wink: )

Well, many "laws" are like that. In science, the word itself generally applies to just the description of some observed behavior, not to an explanation (which would be a theory).

The frame of reference energy dependence is interesting. Would it be correct to then assume that the energy of these CMB photons hasn't really decreased, it's just that they look that way due to the expansion of the universe?

Right. The energy of a photon doesn't change, although the energy we measure depends upon our frame of reference. Photons can be red or blue shifted by cosmological expansion or by changing their position in a gravitational field, but these cases reflect different frames.

Wouldn't that mean that the overall energy of the whole Universe is unchanged due to cooling?

I don't think it's normally suggested that the overall energy of the Universe is changing.
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Re: APOD: Split the Universe (2017 Apr 01

Postby BDanielMayfield » Mon Apr 17, 2017 2:10 pm

Chris Peterson wrote:
Bruce wrote:Wouldn't that mean that the overall energy of the whole Universe is unchanged due to cooling?

I don't think it's normally suggested that the overall energy of the Universe is changing.

My worldview is substantially less rocked, so thanks. But that's not counting Dark Energy, right?

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Re: APOD: Split the Universe (2017 Apr 01

Postby Chris Peterson » Mon Apr 17, 2017 2:18 pm

BDanielMayfield wrote:
Chris Peterson wrote:
Bruce wrote:Wouldn't that mean that the overall energy of the whole Universe is unchanged due to cooling?

I don't think it's normally suggested that the overall energy of the Universe is changing.

My worldview is substantially less rocked, so thanks. But that's not counting Dark Energy, right?

It depends who you talk to. Dark energy is not generally seen as violating conservation of energy, but in some models it does. Because there is little fundamental basis for conservation of energy, that doesn't bother too many cosmologists.
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Wigner's friend

Postby neufer » Sat May 27, 2017 8:48 pm

RJN wrote:
After midnight when the APOD appeared, I showed a person I know hoping to get a "Cool!" response. But this APOD made that person sad. The dead cartoon cat made them remember a recently deceased real cat of which they were fond. Apparently the thought of a dead cat -- and possibly killing a cat -- even a virtual cat -- weighs heavily on people's minds. Oops. And so maybe the tie-in to Schrodinger was less appealing than I thought.
https://en.wikipedia.org/wiki/Wigner%27s_friend wrote:
<<Wigner's friend is a thought experiment proposed by the physicist Eugene Wigner; it is an extension of the Schrödinger's cat experiment. The thought experiment posits a friend of Wigner who performs the Schrödinger's cat experiment after Wigner leaves the laboratory. Only when he returns does Wigner learn the result of the experiment from his friend, that is, whether the cat is alive or dead. The question is raised: was the state of the system a superposition of "dead cat/sad friend" and "live cat/happy friend," only determined when Wigner learned the result of the experiment, or was it determined at some previous point?>>
https://www.mersenne.org/primes/?press=M74207281 wrote:
GIMPS Project Discovers
Largest Known Prime Number: 274,207,281-1

<<On January 7, 2016, at 22:30 UTC, the Great Internet Mersenne Prime Search (GIMPS) celebrated its 20th anniversary with the math discovery of the new largest known prime number, 274,207,281-1, having 22,338,618 digits, on a university computer volunteered by Curtis Cooper for the project. The primality proof took 31 days of non-stop computing on a PC with an Intel I7-4790 CPU. This is the fourth record GIMPS project prime for Dr. Cooper and the University of Central Missouri. Dr. Cooper's computer reported the prime in GIMPS on September 17, 2015 but it remained unnoticed until routine maintenance data-mined it. The official discovery date is the day a human took note of the result. This is in keeping with tradition as M4253 is considered never to have been the largest known prime number because Hurwitz in 1961 read his computer printout backwards and saw M4423 was prime seconds before seeing that M4253 was also prime.>>

A Mersenne prime is a prime number of the form: Mp= 2p-1

We know that M2= 22-1 = 3 is a Mersenne prime
We know that M3= 23-1 = 7 is a Mersenne prime
We know that M7= 27-1 = 127 is a Mersenne prime
We know that M127 = 170,141,183,460,469,231,731,687,303,715,884,105,727 is a Mersenne prime

Neuendorffer Conjecture: M170,141,183,460,469,231,731,687,303,715,884,105,727 is a Mersenne prime. :kitty:
Art Neuendorffer


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