Author Topic: Episode #670  (Read 6969 times)

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Offline bachfiend

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Re: Episode #670
« Reply #75 on: May 18, 2018, 03:12:10 PM »

We'll, evolution is change in a population across generations, so 'de-evolve' must mean not changing?  Which isn't the context it's being used in.  Maybe it means 'to not understand basic evolution'?



[/quot

First, you use a reductive definition of evolve which relies on only part of it's description, then use that minimalist definition to define de-volve, in a way that is not how it's being used in any context.  Then use the misunderstanding you created to insult those who disagree with you.


Utter drivel, carbshark.  I didn't create any misunderstanding,nor did I insult anyone.  People who talk about de-evolving are showing they don't understand evolution.  It's nothing to do with agreeing with me or not, it's about evolution and understanding what evolution is and is not.  You make dumb connections and misunderstand what is being said.

Here's the last post I will make to you.  You are not fun to talk with, and you are not interested in discussing things, only in trying to look clever.  Is totally ignoring you sufficiently minimalist?  (For clarity, that's rhetoric, I really won't read any response you make)

Physicity,

Nonsense.  De-evolution was, and I repeat, was a concept from the early days of the understanding of evolution.  It was realised that changes in populations as a result of natural selection favouring the beneficial changes (later realised to be due to changes in the genome) could be reversed if the changes were reversed with the populations returning to their original forms. 

It’s just extremely unlikely to happen.

As an example, humans evolved to be dependent on dietary intake of vitamin C as a result of a mutation in the final enzyme synthesising vitamin C (not having to bother synthesising vitamin C is an advantage when there’s so much vitamin C in the diet).  Humans could ‘de-evolve’ to become dietary vitamin C independent if another mutation happened reversing the original mutation (but it’s unlikely to happen since there are many more sites in the gene where new mutations could occur - which actually has happened in the 50+ million years since the original mutation occurred, resulting in the gene containing numerous mutations other than the original one, all of which would need to be reversed.  Not bloody likely).
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Offline elert

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Re: Episode #670
« Reply #76 on: May 19, 2018, 02:00:12 PM »
Photons don't have mass and I don't think Woody Allen ever said they did.

Then how do they have momentum?   >:D

How do photons have momentum? Because every moving thing has momentum. The only explanation I know is mathematical.

In general E²=p²c²+m²c⁴. For stationary particles this reduces to the famous E=mc². (Objects at rest have energy.) For massless particles it reduces to E=pc. Since E=hf and f=c/λ, then p=h/λ. (Photons have momentum.)

Offline elert

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Re: Episode #670
« Reply #77 on: May 19, 2018, 11:31:08 PM »
Photons don't have mass and I don't think Woody Allen ever said they did.

No one has any comment on Woody Allen saying (or more probably not saying) this purported quote? I can't find anything approaching an original source to confirm (or more even deny) this.

Offline Redamare

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Re: Episode #670
« Reply #78 on: May 20, 2018, 06:42:08 AM »
They have energy, which is not really distinct from mass.
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Offline CarbShark

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Re: Episode #670
« Reply #79 on: May 20, 2018, 09:29:00 AM »
Photons don't have mass and I don't think Woody Allen ever said they did.


“Photons have mass? I didn't even know they were Catholic.” — Woody Allen


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and Donald Trump is President of the United States.

I'm not a doctor, I'm just someone who has done a ton of research into diet and nutrition.

Offline RMoore

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Re: Episode #670
« Reply #80 on: June 04, 2018, 01:00:35 PM »
Photons don't have mass and I don't think Woody Allen ever said they did.

Then how do they have momentum?   >:D

How do photons have momentum? Because every moving thing has momentum. The only explanation I know is mathematical.

In general E²=p²c²+m²c⁴. For stationary particles this reduces to the famous E=mc². (Objects at rest have energy.) For massless particles it reduces to E=pc. Since E=hf and f=c/λ, then p=h/λ. (Photons have momentum.)

An object's momentum is its mass times its velocity, in Newtonian physics (where mass just means rest mass). In relativistic physics, simply replace the formula with relativistic mass times velocity. We can verify that photons have momentum by observing that they can transfer momentum to other objects. Divide the measured momentum by the velocity and you get its (relativistic) mass.

If you insist on being a Newtonian after such an experiment, then you either need to assume that photons have a non-zero rest mass, or that they travel at infinite speed. But either way doesn't spare you from other conflicts between reality and Newtonian physics.

Offline brilligtove

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Re: Episode #670
« Reply #81 on: June 04, 2018, 01:37:05 PM »
I didn't realize we were having this conversation in e670 and e671 threads. Maybe this should all be in a 'Physics of light, mass, and time' thread?

PBS Spacetime has a lot of great videos about topics like this. I'm pretty sure they have one about mass vs rest mass... Yup.



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Offline elert

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Re: Episode #670
« Reply #82 on: June 09, 2018, 03:13:37 PM »
Photons don't have mass and I don't think Woody Allen ever said they did.


“Photons have mass? I didn't even know they were Catholic.” — Woody Allen


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Source, please. (Original source, please.)

Offline Ron Obvious

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Re: Episode #670
« Reply #83 on: June 09, 2018, 03:45:40 PM »
Photons don't have mass and I don't think Woody Allen ever said they did.


“Photons have mass? I didn't even know they were Catholic.” — Woody Allen


Sent from my iPhone using Tapatalk

Source, please. (Original source, please.)

Oh, FFS.

Offline elert

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Re: Episode #670
« Reply #84 on: June 09, 2018, 04:12:22 PM »
Photons don't have mass and I don't think Woody Allen ever said they did.

Then how do they have momentum?   >:D

How do photons have momentum? Because every moving thing has momentum. The only explanation I know is mathematical.

In general E²=p²c²+m²c⁴. For stationary particles this reduces to the famous E=mc². (Objects at rest have energy.) For massless particles it reduces to E=pc. Since E=hf and f=c/λ, then p=h/λ. (Photons have momentum.)

An object's momentum is its mass times its velocity, in Newtonian physics (where mass just means rest mass). In relativistic physics, simply replace the formula with relativistic mass times velocity. We can verify that photons have momentum by observing that they can transfer momentum to other objects. Divide the measured momentum by the velocity and you get its (relativistic) mass.

If you insist on being a Newtonian after such an experiment, then you either need to assume that photons have a non-zero rest mass, or that they travel at infinite speed. But either way doesn't spare you from other conflicts between reality and Newtonian physics.

In the early days of relativity, the terms "longitudinal mass" and "transverse mass" were used when it was thought that Newton's 2nd law should be expressed using the equation F=ma. Later on the consensus was that F=dp/dt is more fundamentally correct and that p=γmv is the (for lack of a better word) right way to define momentum. No one uses the terms longitudinal and transverse in regards to mass anymore, but sometime around 1920 the term "relativistic mass" popped up. This came from textbook authors (among them Wolfgang Pauli) who assumed that p=γmv should be read as p=(γm)v implying that mass is "relativistic" (m'=γm) in the same way that time and distance are — as in time dilation (t'=γt) and length contraction (l'=l/γ). Other than his initial use of the terms longitudinal mass and transverse mass, Einstein never referred to relativistic mass in any public writing. (He did write a letter to a colleague saying that such a concept has no clear definition, however.)

Relativistic mass and rest mass are not useful concepts since mass is Lorentz invariant. Mass is just mass. Energy, on the other hand, is affected by relative motion, which is why relativistic energy (E=γmc²) and rest energy (E₀=mc²) are still valid as is mass-energy conversion (∆E=∆mc²). Objects don't gain mass as their speed increases, nor do photons have mass. In every correct sense of the word mass, photons are massless.

Offline elert

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Re: Episode #670
« Reply #85 on: June 09, 2018, 04:17:40 PM »
Photons don't have mass and I don't think Woody Allen ever said they did.

Then how do they have momentum?   >:D

Photons do not have rest mass. They do have mass related to the amount to energy the photon is packing. http://www.physlink.com/education/askexperts/ae180.cfm  >:D :love: >:D

This reference is wrong.

 

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