Ask a Theoretical Physicist

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Re: Ask a Theoretical Physicist

Postby Joseph Stalin » Mon Sep 01, 2014 12:17 am

aviel wrote:
Joseph Stalin wrote:What do you mean by falsifiable?

We can, at least with better technology, do experiments to test whether or not it is true.

String theory is not experimentally falsifiable with any conceivable technology, but then no theory which deals with so high energies is.
String theory is falsifiable in principle. For instance, I mentioned the entropy calculations of a certain black hole. This is a prediction.

I may be misunderstanding the issue, but isn't that a post-diction? Did we not already know it and string theory uncovered it? Also, I heard that quantum loop gravity was at least falsifiable. Is that untrue?


Which part is a post-diction? Do you mean reduction of string theory to know theories? Well, it is basic consistency check. It is a very important feature of the theory. If you want something really new string theory predicts supersymmetry.
Loop quantum gravity fails to reduce to know theories. It has no connection to particle physics. It's main prediction is Lorentz violation at high energies. If I recall correctly Lorentz violation up to almost Planck scales has been experimentally falsified recently by some gamma ray burst observations. LQG is looking worse after this.
This experiment has also shown string theory's prediction that Lorentz invariance holds at all energies to be correct.
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Re: Ask a Theoretical Physicist

Postby Learned Nand » Mon Sep 01, 2014 1:36 am

Joseph Stalin wrote:Which part is a post-diction?

Sorry, I quoted the wrong bit. I meant the calculation of the entropy of black holes.

Loop quantum gravity fails to reduce to know theories. It has no connection to particle physics. It's main prediction is Lorentz violation at high energies. If I recall correctly Lorentz violation up to almost Planck scales has been experimentally falsified recently by some gamma ray burst observations. LQG is looking worse after this.
This experiment has also shown string theory's prediction that Lorentz invariance holds at all energies to be correct.

Right, I'm just asking because you said no theory about these things was falsifiable, and it seems LQG has been falsified.
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Terry Pratchett wrote:The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it.

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Re: Ask a Theoretical Physicist

Postby Joseph Stalin » Mon Sep 01, 2014 2:28 am

aviel wrote:
Joseph Stalin wrote:Which part is a post-diction?

Sorry, I quoted the wrong bit. I meant the calculation of the entropy of black holes.

Loop quantum gravity fails to reduce to know theories. It has no connection to particle physics. It's main prediction is Lorentz violation at high energies. If I recall correctly Lorentz violation up to almost Planck scales has been experimentally falsified recently by some gamma ray burst observations. LQG is looking worse after this.
This experiment has also shown string theory's prediction that Lorentz invariance holds at all energies to be correct.

Right, I'm just asking because you said no theory about these things was falsifiable, and it seems LQG has been falsified.

Well, not quite, because one needs to reach Planck scale to get 100% falsification, which is not possible. The situation is not looking good though.
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Re: Ask a Theoretical Physicist

Postby Learned Nand » Mon Sep 01, 2014 5:12 am

Is reaching the Planck scale literally not possible because you can only do it at the limit, or is it practically not possible because it would require a particle accelerator powered by a dyson sphere encompassing the entire galaxy?
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Terry Pratchett wrote:The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it.

Click for a Limerick
OrangeEyebrows wrote:There once was a guy, Aviel,
whose arguments no one could quell.
He tested with Turing,
his circuits fried during,
and now we'll have peace for a spell.
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Re: Ask a Theoretical Physicist

Postby Joseph Stalin » Mon Sep 01, 2014 6:19 pm

aviel wrote:Is reaching the Planck scale literally not possible because you can only do it at the limit, or is it practically not possible because it would require a particle accelerator powered by a dyson sphere encompassing the entire galaxy?


The experiment I discussed, observing photons from gamma ray bursts is impossible in principle at order of magnitude Planck energy - everything becomes a black hole at that energy.
Using an accelerator to probe those energies will likely forever be impossible. With current technology one would need an accelerator somewhere around 1000 times larger the the Milky Way (I did a back of the envelope calculation just now). If technology improves say by 10^5 (this is really somewhere around theoretical maximum due to properties of materials) it would still be too huge to pull off for any conceivable civilization.
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Re: Ask a Theoretical Physicist

Postby RedBearded » Tue Sep 02, 2014 6:08 am

Joseph Stalin wrote:Well. My day looks like this. I go to work and then get some coffee


How does the Man of Steel take his coffee?
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Re: Ask a Theoretical Physicist

Postby Joseph Stalin » Tue Sep 02, 2014 1:47 pm

RedBearded wrote:
Joseph Stalin wrote:Well. My day looks like this. I go to work and then get some coffee


How does the Man of Steel take his coffee?


Triple espresso, of course, no milk/sugar. The only coffee potent enough to wake up STALIN.
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Re: Ask a Theoretical Physicist

Postby NathanLoiselle » Tue Sep 02, 2014 10:02 pm

That's how I take my coffee!
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Re: Ask a Theoretical Physicist

Postby Learned Nand » Tue Sep 02, 2014 10:14 pm

NathanLoiselle wrote:That's how I take my coffee!

Commie bastard.
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Terry Pratchett wrote:The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it.

Click for a Limerick
OrangeEyebrows wrote:There once was a guy, Aviel,
whose arguments no one could quell.
He tested with Turing,
his circuits fried during,
and now we'll have peace for a spell.
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Re: Ask a Theoretical Physicist

Postby Deathclaw_Puncher » Tue Sep 02, 2014 10:28 pm

Someone get Nathan a good ol' American, capitalist coffee, like a mocha verrite:
Spoiler: show
espresso over steamed half and half and an ounce of chocolate syrup. It's the fattest hot espresso drink, with round 63 grams of fat per serving.
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Re: Ask a Theoretical Physicist

Postby Joseph Stalin » Tue Sep 02, 2014 10:39 pm

Ericthebearjew wrote:Someone get Nathan a good ol' American, capitalist coffee, like a mocha verrite:
Spoiler: show
espresso over steamed half and half and an ounce of chocolate syrup. It's the fattest hot espresso drink, with round 63 grams of fat per serving.


Stalin never got the point of mixing coffee with other stuff like chocolate or bananas. You just ruin both.
Stalin like cheeseburger and Stalin like ice cream, but Stalin not want ice cream in cheeseburger, you know?
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Re: Ask a Theoretical Physicist

Postby RedBearded » Wed Sep 03, 2014 3:22 am

Joseph Stalin wrote:Triple espresso, of course, no milk/sugar. The only coffee potent enough to wake up STALIN.


Black and strong no extra's is my way also. Long live the proletariat. Now to get your thread somewhat back on course.

When?
Image
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Re: Ask a Theoretical Physicist

Postby Joseph Stalin » Wed Sep 03, 2014 3:50 am

RedBearded wrote:
Joseph Stalin wrote:Triple espresso, of course, no milk/sugar. The only coffee potent enough to wake up STALIN.


Black and strong no extra's is my way also. Long live the proletariat. Now to get your thread somewhat back on course..

Yes. All glory to the international working class!

RedBearded wrote:When?
Image


Probably when/if they make room temperature superconductors and magnetic roads. Since even slightly higher than ordinary temperature superconductors (somewhere above 30 K) are not yet theoretically understood (there is a Nobel prize waiting for anyone who can do it) it could be tomorrow and it could be never.
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Re: Ask a Theoretical Physicist

Postby Readersprite » Tue Sep 09, 2014 1:13 am

How does one become a theoretical physicist? Or at least, how did you get into your field/career? Education and so forth? Thanks!

Sorry if my question is too dull or irrelevant to the thread.
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Re: Ask a Theoretical Physicist

Postby Joseph Stalin » Tue Sep 09, 2014 2:28 am

Readersprite wrote:How does one become a theoretical physicist? Or at least, how did you get into your field/career? Education and so forth? Thanks!

Sorry if my question is too dull or irrelevant to the thread.


No, no. I'll be glad to answer any question I can. I think this is a very good question.

I knew I wanted to be a scientist since I was a kid. Before I could read my mother used to read to me from children's encyclopedias and everything about the natural world fascinated me. I especially liked learning about dinosaurs, tsunamis and (for some reason) ammonia. We also did little experiments together, etc.
Then later when I learned to read I stared to read pop sci books about physics by myself and I firmly decided that I wanted to be a theoretical physicist.
I followed up on those wishes by going to a math specialized high school and later going to university and majoring in physics.
When I finished my undergraduate studies I got a job as a research assistant and did my PhD. I didn't choose my particular field rather I choose which group I would work with (and which wanted me of course). My requirement was that it was a theoretical group and did high-quality research.
Today theoretical physics is highly specialized - you have people doing high energy (i.e., string theory), gravity, cosmology, condensed matter, biophysics/soft matter, quantum information theory, mathematical physics even econophysics, etc. etc.
I'm quite happy that I found my niche and also got to dabble in several of these interesting fields because I want to have a broad overview of physics as a whole.
The path to become a theoretical physicist is - majoring in physics (maybe math) at university and going on to do a PhD in theoretical physics. This is a difficult path. Mostly because of financial reasons and the difficulty of the job. No matter how smart you are there will always be some problem that is too difficult for you to solve (obviously or we would know everything) so the trick is to find the hardest possible (and most interesting) problem that you can solve and then solve it. This means that the greatest geniuses are doing stellar research but they still have to work as hard as the average physicist doing mediocre stuff.
What ones does afterwards is not so easy either. You are almost always expected to find a low paying temporary 2-4 year position as a "postdoctoral researcher" (postdoc). Permanent positions are almost impossible to find these days and if you get one it will likely be somewhere you don't want to be. Physics, and science in general, is not respected as much as it used to be. But I don't want to bum you out.
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Arise, you prisoners of starvation!
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A better world's in birth!
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