# Neutrino experiment repeat at Cern finds same result (Faster than Light)

Cpt_pineapple
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Neutrino experiment repeat at Cern finds same result (Faster than Light)

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# Neutrino experiment repeat at Cern finds same result

Neutrinos travel through 700km of rock before reaching Gran Sasso's underground laboratories

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The team which found that neutrinos may travel faster than light has carried out an improved version of their experiment - and confirmed the result.

If confirmed by other experiments, the find could undermine one of the basic principles of modern physics.

Critics of the first report in September had said that the long bunches of neutrinos (tiny particles) used could introduce an error into the test.

The new work used much shorter bunches.

It has been posted to the Arxiv repository and submitted to the Journal of High Energy Physics, but has not yet been reviewed by the scientific community.

The experiments have been carried out by the Opera collaboration - short for Oscillation Project with Emulsion (T)racking Apparatus.

It hinges on sending bunches of neutrinos created at the Cern facility (actually produced as decays within a long bunch of protons produced at Cern) through 730km (454 miles) of rock to a giant detector at the INFN-Gran Sasso laboratory in Italy.

The initial series of experiments, comprising 15,000 separate measurements spread out over three years, found that the neutrinos arrived 60 billionths of a second faster than light would have, travelling unimpeded over the same distance.

The idea that nothing can exceed the speed of light in a vacuum forms a cornerstone in physics - first laid out by James Clerk Maxwell and later incorporated into Albert Einstein's theory of special relativity.

Timing is everything

Initial analysis of the work by the wider scientific community argued that the relatively long-lasting bunches of neutrinos could introduce a significant error into the measurement.

Those bunches lasted 10 millionths of a second - 160 times longer than the discrepancy the team initially reported in the neutrinos' travel time.

To address that, scientists at Cern adjusted the way in which the proton beams were produced, resulting in bunches just three billionths of a second long.

When the Opera team ran the improved experiment 20 times, they found almost exactly the same result.

"This is reinforcing the previous finding and ruling out some possible systematic errors which could have in principle been affecting it," said Antonio Ereditato of the Opera collaboration.

"We didn't think they were, and now we have the proof," he told BBC News. "This is reassuring that it's not the end of the story."

The first announcement of evidently faster-than-light neutrinos caused a stir worldwide; the Opera collaboration is very aware of its implications if eventually proved correct.

The error in the length of the bunches, however, is just the largest among several potential sources of uncertainty in the measurement, which must all now be addressed in turn; these mostly centre on the precise departure and arrival times of the bunches.

"So far no arguments have been put forward that rule out our effect," Dr Ereditato said.

"This additional test we made is confirming our original finding, but still we have to be very prudent, still we have to look forward to independent confirmation. But this is a positive result."

That confirmation may be much longer in coming, as only a few facilities worldwide have the detectors needed to catch the notoriously flighty neutrinos - which interact with matter so rarely as to have earned the nickname "ghost particles".

Next year, teams working on two other experiments at Gran Sasso experiments - Borexino and Icarus - will begin independent cross-checks of Opera's results.

The US Minos experiment and Japan's T2K experiment will also test the observations. It is likely to be several months before they report back.

redneF
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Vastet wrote: Really odd

Vastet wrote:
Really odd being told I'm wrong

You were never wrong. Your statements are sound and accurate.

She's not arguing the statement that you made, she's arguing what she'd like to think you meant when you stated it. She's better than that. I don't know why she's arguing against your statements.

I wish she'd drop it.

She can obviously add to our understanding, for us laypersons.

I keep asking myself " Are they just playin' stupid, or are they just plain stupid?..."

"To explain the unknown by the known is a logical procedure; to explain the known by the unknown is a form of theological lunacy" : David Brooks

" Only on the subject of God can smart people still imagine that they reap the fruits of human intelligence even as they plow them under." : Sam Harris

FurryCatHerder
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Vastet wrote:Really odd

Vastet wrote:
Really odd being told I'm wrong then given evidence I'm right, repeatedly in a single topic. I've reread the thread a few times now and can only shake my head at Furry's breakdown into an absolutely irrational argument in this thread. The worst part is that most of her science is right, until she suggests I was wrong when I said temperature was everywhere then writes paragraphs proving it IS everywhere. Lol is the only appropriate response.

Alright, I'm going to explain why you're wrong, and why it seems you're right, based on a lay-persons understanding of the science.  Hopefully this will shut you up =and= contribute to the general understanding of such things.

In Mathematics there is a concept called a "limit".  We say "the limit of such-and-such equation, such this variable goes to some value, is some other value."  For example, the limit of 1 / x as x goes to infinity, is 0.  As you pick bigger and bigger numbers, the result of 1/x becomes smaller and smaller.  But that DOES NOT mean that the value =is= zero.  Here, read this --

What you need to pay very careful attention to the highlighted sentence --

Suppose f(x) is a real-valued function and c is a real number. The expression

$\lim_{x \to c}f(x) = L$

means that f(x) can be made to be as close to L as desired by making x sufficiently close to c. In that case, it can be stated that "the limit of f of x, as x approaches c, is L". Note that this statement can be true even if f(c) ≠ L. Indeed, the function f(x) need not even be defined at c.

And here's an example of that --

For example, if

$f(x) = \frac{x^2 - 1}{x - 1}$

then f(1) is not defined (see division by zero), yet as x moved arbitrarily close to 1, f(x) correspondingly approaches 2:

 f(0.9) f(0.99) f(0.999) f(1.0) f(1.001) f(1.01) f(1.1) 1.900 1.990 1.999 ⇒ undef ⇐ 2.001 2.010 2.100

Thus, f(x) can be made arbitrarily close to the limit of 2 just by making x sufficiently close to 1.

In that example, the LIMIT of f(x) as x approaches 1 is 2, but the VALUE of f(x), when x == 1, is undefined.  Get your calculator out and try those examples.  I'll show you three of them --

f(.9) = (.9^2 - 1) / (.9 - 1) = (0.81 - 1) / (.9 - 1) = -0.19 / -0.1 = 1.9

f(1) = (1^2 - 1) / (1 - 1) = (1 - 1) / (1 - 1) = 0 / 0.

f(1.1) = (1.1 ^ 2 - 1) / (1.1 - 1) = (1.21 - 1) / (1.1 - 1) = .21 / .1 = 2.1

Hmmmmm.  Notice something happened in the middle?

The easiest way to show that the answer is "undefined" or "indeterminate" is that the temperature of a something is the average of the temperatures of all the individual somethings.  Since an average is the total of the measurements divided by the number of measurements, in a complete and total vacuum, the number of measurements is zero, and division of any number by zero is undefined.

QED, the temperature of a hypothetical perfect vacuum =is= undefined.

Now, why lay person explanations are misleading --

You understood all that stuff about limits?  Yes?  No?  If the answer is "No", and for most lay people it =is= "No", and you still want an answer, I'll give you an =incorrect= answer, knowing that you haven't a clue why it's incorrect precisely because you'll never understand the correct answer.  If you think you actually understand limits, the answer is it's undefined.

"Obviously I'm convinced of the existence of G-d. I'm equally convinced that Atheists who've led good lives will be in Olam HaBa going "How the heck did I wind up in this place?!?" while Christians who've treated people like dirt will be in some other place asking the exact same question."

Vastet
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At least I see where you're

At least I see where you're arguing from now.
However, for the average person, my statement is sufficient. It just isn't a completely and totally accurate description. Which is something I'd have admitted to if you had corrected instead of slandered me.
I've done so a number of times, with complicated science I try to simplify for the average reader which loses a bit of accuracy in order to gain communicability, only to have someone jump in with a more comprehensive answer.
As I'm sure you're aware, the average person one comes into contact with isn't going to walk through a wall of calculus and come out understanding it. So I don't assume they will. I therefore tend to treat 0k as an actual temperature in my statements, amongst other things. It's a lot easier to get the point across. And it takes a lot less writing.

It'd have been nice for you to start here, but at least you did finally respond to a statement I made without relying completely on ad hom and insufficient explanation. I appreciate that.

Once-Proud Canadian, Enlightened Atheist, Gaming God.

Ktulu
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I admire your overly

I admire your overly complicated justification and attempt at sounding overly educated and intelligent.  You are of course correct, but not because you repackaged the turd in tin foil.  Here is what Wiki which everyone is so fond of has to say regarding a vacuum.

wiki wrote:
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure.[1] The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in practice. Physicists often discuss ideal test results that would occur in a perfect vacuum, which they simply call "vacuum" or "free space", and use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space. The Latin term in vacuo is also used to describe an object as being in what would otherwise be a vacuum.

Here's what wiki has to say about temperature.

wiki wrote:
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot. Heat spontaneously flows from bodies of a higher temperature to bodies of lower temperature, and no net heat will be exchanged between bodies of the same temperature. Such bodies are said to be in "thermal equilibrium".

Now, while your explanation is both silly, irrelevant and not applicable, it was rather educational.  Relative to how a narcissistic personality justifies itself.

In conclusion TEMPERATURE is a physical property of matter.  VACUUM is void of all matter.  I'm not sure why this is a debate...

"Don't seek these laws to understand. Only the mad can comprehend..." -- George Cosbuc

Vastet
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And yet there is no such

And yet there is no such thing as a perfect vacuum, so it's irrelevant that matter is necessary for temperature as there is matter in a vacuum.
As irrelevant as are your amusing attempts to diagnose my personality and pretend to be smart yet only jumping in after the dust has settled yet still fail to contribute anything of value.

And I'm the narcissist? LOL

Once-Proud Canadian, Enlightened Atheist, Gaming God.

Ktulu
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Vastet wrote:And yet there

Vastet wrote:
And yet there is no such thing as a perfect vacuum, so it's irrelevant that matter is necessary for temperature as there is matter in a vacuum. As irrelevant as are your amusing attempts to diagnose my personality and pretend to be smart yet only jumping in after the dust has settled yet still fail to contribute anything of value. And I'm the narcissist? LOL

I don't think you are skilled enough in sophistry to be a narcissist.  It was directed at Furry.  And yet, in a previous post, as well as in the definition i have stated that a practical perfect vacuum is impossible.

However, when one says the speed of light in a vacuum, one infers a theoretical vacuum.  Otherwise you have to refer your parameters for the imperfect vacuum and calculate their impact on what you are trying to prove.  It wouldn't be very practical in physics.  So when one says the word VACUUM especially when talking about physics, one means a THEORETICAL VACUUM.  If you then attempt to quantify and argue over a property of matter (namely temperature) in a medium that is by definition void of all matter (namely a theoretical vacuum) is at best futile and at worst idiotic.  The fact that Furry came up with a sophisticated reason why she was correct makes her skilled in sophistry, and correct for the wrong reason.

I usually skip over your posts unless they're directed at me, so I'm not even sure what your position was, though I'm sure it was firmly based on reason.

"Don't seek these laws to understand. Only the mad can comprehend..." -- George Cosbuc

FurryCatHerder
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redneF,I'm trying to get you

redneF,

I'm trying to get you away from "velocity", and now that I understand better where you're heading, away from photons, because "photons" don't work like atoms or other (hadronparticles.

Consider, for example, the solar wind and the light coming from the sun.  When a solar flare happens, the velocity of the solar wind increases, and its temperature increases.  But the speed of light from that flare stays the same.  A photon a boson, and a proton (what much of the solar wind is made of) is a hadron.  One has mass, the other doesn't.  For one, the energy is related to the  velocity (proton), for the other, the energy is related to the frequency (photons).  Here's the current space weather --

So, at the time I captured that page, the =matter= in the solar wind was going 400,000 meters per second, and the =light= was going 300,000,000 meters per second.  If the solar wind dies down, the temperature goes down, the velocity goes down, but the speed is still 300,000,000 meters per second.

What happens to photons as their temperature (frequency) increases?  Well, their frequency increases and the wave length decreases, but the =velocity= remains the same.  As I understand such things, when the wavelength (inverse of frequency) reaches the Plank Length, that's it -- no more increase in  energy is possible.

The other thing that happens is that high energy photons that interact with "something" can convert some of that energy (temperature) to matter using E = mc2.  An electron has a rest mass of 511keV.  So, a photon with an energy of more than 1.022MeV could produce an electron (e-) and a positron (e+).  Above 1.9GeV or so, it could produce a proton and antiprotron.

"Obviously I'm convinced of the existence of G-d. I'm equally convinced that Atheists who've led good lives will be in Olam HaBa going "How the heck did I wind up in this place?!?" while Christians who've treated people like dirt will be in some other place asking the exact same question."

FurryCatHerder
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Vastet wrote:At least I see

Vastet wrote:
At least I see where you're arguing from now.

And if you were qualified to even have this discussion, you'd have known the answer from the start.

Being an Atheist is accidental to your being unqualified to discuss science AT ALL.  But you use being an Atheist much the same way a drunk uses a lamp post.

"Obviously I'm convinced of the existence of G-d. I'm equally convinced that Atheists who've led good lives will be in Olam HaBa going "How the heck did I wind up in this place?!?" while Christians who've treated people like dirt will be in some other place asking the exact same question."

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Ktulu wrote:The fact that

Ktulu wrote:
The fact that Furry came up with a sophisticated reason why she was correct makes her skilled in sophistry, and correct for the wrong reason.

I love being told I'm right for the wrong reasons by someone who quotes answers from Wikipedia.

Care to explain, without quoting Wikipedia, why the temperature of a vacuum is undefined?  For all of Vastet's failings, and they are many, Appeal to Authority doesn't seem to be one of the fallacies he falls for.

"Obviously I'm convinced of the existence of G-d. I'm equally convinced that Atheists who've led good lives will be in Olam HaBa going "How the heck did I wind up in this place?!?" while Christians who've treated people like dirt will be in some other place asking the exact same question."

ProzacDeathWish
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Vastet, here's a quote

Vastet, here's a quote from Irish playwright George Bernard Shaw, a wise man if their ever was one....

"I learned long ago, never to wrestle with a pig.  You get dirty, and besides, the pig likes it."

"The only power any government has is the power to crack down on criminals. Well, when there aren't enough criminals, one makes them. One declares so many things to be a crime that it becomes impossible for men to live without breaking laws."
Ayn Rand

Ktulu
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FurryCatHerder wrote:Ktulu

FurryCatHerder wrote:

Ktulu wrote:
The fact that Furry came up with a sophisticated reason why she was correct makes her skilled in sophistry, and correct for the wrong reason.

I love being told I'm right for the wrong reasons by someone who quotes answers from Wikipedia.

Care to explain, without quoting Wikipedia, why the temperature of a vacuum is undefined?  For all of Vastet's failings, and they are many, Appeal to Authority doesn't seem to be one of the fallacies he falls for.

Ktulu wrote:

In conclusion TEMPERATURE is a physical property of matter.  VACUUM is void of all matter.  I'm not sure why this is a debate...

Am I the only one that finds this plainly simple and a non issue? the fact that I quoted wiki is to get any definition in there.  I will be the first to admit that I am a layman relative to physics, I will also be the first to admit that you likely do have more knowledge of physics than I do.

The issue that we're having here is semantics.

You are all arguing about imperfect vacuums.  An imperfect vacuum is something that contains SOMETHING.  If you are not referring to a perfect vacuum, simply define the imperfection and the temperature would be calculated depending on the imperfection.

If you are referring to a theoretical vacuum (which you are,  you just don't want to admit it to support whatever you came up with) then it is a moot question.  I know that you dwell into eastern practices, so the answer is, the temperature of a vacuum is the sound of one hand clapping.

"Don't seek these laws to understand. Only the mad can comprehend..." -- George Cosbuc

Vastet
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Ktulu wrote: It was

Ktulu wrote:
It was directed at Furry.

My apologies. The timing of your post and its lack of a direct and unambiguous target lead to an assumption.

Furry wrote:
And if you were qualified to even have this discussion, you'd have known the answer from the start.

The irony being that I DID know this answer from the start. It merely has little value in common discourse. If you hadn't been so quick to throw punches and assume I didn't know what I was talking about an entire page of this topic wouldn't even exist.

Prozac wrote:
Vastet, here's a quote from Irish playwright George Bernard Shaw, a wise man if their ever was one....

I learned some time ago that getting dirty is inevitable, so you may as well learn to enjoy it.

Once-Proud Canadian, Enlightened Atheist, Gaming God.

Sage_Override
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Someone mentioned their

Someone mentioned their obsession with time travel in this thread and hoping it will, one day, be possible.  Stephen Hawking explained the concept of time travel and why it wouldn't work going BACKWARDS, but supports the overall theory of moving FORWARD.  He was mentioned in an article showcasing some of his theories and breaking it down in some simple terms.  I'll try to find it and share it; it was really neat.  http://www.dailymail.co.uk/sciencetech/article-1270531/Stephen-Hawking-backs-possibility-time-travel-millions-years-future.html

"When the majority believes in what is false, the truth becomes a quest." - Me

luca
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shwha

Quote:
when the wavelength (inverse of frequency) reaches the Plank Length, that's it -- no more increase in energy is possible

Could it really happen? Could the frequency of an electromagnetic wave rise to that point?

Ktulu
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luca wrote:Quote:when the

luca wrote:
Quote:
when the wavelength (inverse of frequency) reaches the Plank Length, that's it -- no more increase in energy is possible
Could it really happen? Could the frequency of an electromagnetic wave rise to that point?

Of course it can, I have a setup in my basement with two double D's and two nipple clamps.  It's fun, educational and cutting edge particle physics.  Billion dollar particle accelerator my ass, I can hack it with a 10 dollar Radio Shack gift card

"Don't seek these laws to understand. Only the mad can comprehend..." -- George Cosbuc

Kapkao
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Sage_Override wrote:Someone

Sage_Override wrote:

Someone mentioned their obsession with time travel in this thread and hoping it will, one day, be possible.  Stephen Hawking explained the concept of time travel and why it wouldn't work going BACKWARDS, but supports the overall theory of moving FORWARD.  He was mentioned in an article showcasing some of his theories and breaking it down in some simple terms.  I'll try to find it and share it; it was really neat.  http://www.dailymail.co.uk/sciencetech/article-1270531/Stephen-Hawking-backs-possibility-time-travel-millions-years-future.html

Since I know fuck-all (nothing) about Hawking's various theories (and when dumbed down they read like complete garbage), I don't care for reading about them from the Daily Mail. I do appreciate the hotlink, however.

It explains a few things I couldn't about time travel being an 80s myth.

“A meritocratic society is one in which inequalities of wealth and social position solely reflect the unequal distribution of merit or skills amongst human beings, or are based upon factors beyond human control, for example luck or chance. Such a society is socially just because individuals are judged not by their gender, the colour of their skin or their religion, but according to their talents and willingness to work, or on what Martin Luther King called 'the content of their character'. By extension, social equality is unjust because it treats unequal individuals equally.” "Political Ideologies" by Andrew Heywood (2003)

FurryCatHerder
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luca wrote:Quote:when the

luca wrote:
Quote:
when the wavelength (inverse of frequency) reaches the Plank Length, that's it -- no more increase in energy is possible
Could it really happen? Could the frequency of an electromagnetic wave rise to that point?

I've never read anything which would indicated it would be impossible, though it would be nigh on impossible.  Specifically, since the energy of a photon is inversely proportional to the wavelength, as the wavelength went from two Plank lengths to one Plank length, the energy would have to double.

One practical problem is that a photon with that much energy would exert a huge gravitational attraction on anything anywhere near it, and if it interacts with anything, it would immediately release large numbers of massive particles.

"Obviously I'm convinced of the existence of G-d. I'm equally convinced that Atheists who've led good lives will be in Olam HaBa going "How the heck did I wind up in this place?!?" while Christians who've treated people like dirt will be in some other place asking the exact same question."

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Sage_Override wrote:Someone

Sage_Override wrote:

Someone mentioned their obsession with time travel in this thread and hoping it will, one day, be possible.  Stephen Hawking explained the concept of time travel and why it wouldn't work going BACKWARDS, but supports the overall theory of moving FORWARD.  He was mentioned in an article showcasing some of his theories and breaking it down in some simple terms.  I'll try to find it and share it; it was really neat.  http://www.dailymail.co.uk/sciencetech/article-1270531/Stephen-Hawking-backs-possibility-time-travel-millions-years-future.html

Going backwards would seem to violate the First Law of Thermodynamics.  At time T the total energy of the Universe is X, at time T - 1 the total energy of the Universe is increased by E = mc^2 of however much mass is transported backwards.  Hawking focuses on Causality, but if the person were REALLY CAREFUL (see "Back To The Future" movies ...) they might avoid the Causality paradox.

But they can't avoid the First Law!  That alone seems to make it a big no-no.

"Obviously I'm convinced of the existence of G-d. I'm equally convinced that Atheists who've led good lives will be in Olam HaBa going "How the heck did I wind up in this place?!?" while Christians who've treated people like dirt will be in some other place asking the exact same question."

redneF
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FurryCatHerder

FurryCatHerder wrote:

Sage_Override wrote:

Someone mentioned their obsession with time travel in this thread and hoping it will, one day, be possible.  Stephen Hawking explained the concept of time travel and why it wouldn't work going BACKWARDS, but supports the overall theory of moving FORWARD.  He was mentioned in an article showcasing some of his theories and breaking it down in some simple terms.  I'll try to find it and share it; it was really neat.  http://www.dailymail.co.uk/sciencetech/article-1270531/Stephen-Hawking-backs-possibility-time-travel-millions-years-future.html

Going backwards would seem to violate the First Law of Thermodynamics.  At time T the total energy of the Universe is X, at time T - 1 the total energy of the Universe is increased by E = mc^2 of however much mass is transported backwards.  Hawking focuses on Causality, but if the person were REALLY CAREFUL (see "Back To The Future" movies ...) they might avoid the Causality paradox.

But they can't avoid the First Law!  That alone seems to make it a big no-no.

Even with a basic 'not so current' understanding of space/time you can model how problematic it is to 'roll' back the 'carpet' once it's been laid out.

Even Hawkings gave the simple thought experiment that if you were to be able to travel back in time, that would mean that you could go back into the past and shoot yourself dead...but then how go you get to the future in order to go back in time to shoot yourself dead...

I keep asking myself " Are they just playin' stupid, or are they just plain stupid?..."

"To explain the unknown by the known is a logical procedure; to explain the known by the unknown is a form of theological lunacy" : David Brooks

" Only on the subject of God can smart people still imagine that they reap the fruits of human intelligence even as they plow them under." : Sam Harris

Sage_Override
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Quote:Since I know fuck-all

Quote:

Since I know fuck-all (nothing) about Hawking's various theories (and when dumbed down they read like complete garbage), I don't care for reading about them from the Daily Mail. I do appreciate the hotlink, however.

It explains a few things I couldn't about time travel being an 80s myth.

You should probably read into his theories then.  Also, I'm glad you appreciate the link, but what does it being from the Daily Mail have to do with anything?  Are they notorious for posting shit that is simplified too much?

"When the majority believes in what is false, the truth becomes a quest." - Me

ProzacDeathWish
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Ktulu wrote:I love it when

Ktulu wrote:

I love it when interesting scientific discussions turn into second grade sandbox name calling.  It's such an intellectual stimulating activity, much like chimp poo flinging.  And a theoretical vacuum has no temperature....

Ktulu, thanks for pointing out my lapse in judgement in allowing myself to being distracted by petty emotions.  Please feel free to express the same sentiment to the highly intellectual rednef in his most recent exchanges with Brian37  ....I wouldn't recommend it, though.

"The only power any government has is the power to crack down on criminals. Well, when there aren't enough criminals, one makes them. One declares so many things to be a crime that it becomes impossible for men to live without breaking laws."
Ayn Rand

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redneF wrote:FurryCatHerder

redneF wrote:

FurryCatHerder wrote:

Going backwards would seem to violate the First Law of Thermodynamics.  At time T the total energy of the Universe is X, at time T - 1 the total energy of the Universe is increased by E = mc^2 of however much mass is transported backwards.  Hawking focuses on Causality, but if the person were REALLY CAREFUL (see "Back To The Future" movies ...) they might avoid the Causality paradox.

But they can't avoid the First Law!  That alone seems to make it a big no-no.

Even with a basic 'not so current' understanding of space/time you can model how problematic it is to 'roll' back the 'carpet' once it's been laid out.

Even Hawkings gave the simple thought experiment that if you were to be able to travel back in time, that would mean that you could go back into the past and shoot yourself dead...but then how go you get to the future in order to go back in time to shoot yourself dead...

I've read the Causality explanation before, but it always relies on arguments like 'don't shoot your grandfather before your father is born".  If I promise not to shoot my grandfather, then can I go?  I suspect there are other, more fundamental Causality issues that can't be avoided, so I don't know if Hawking is simplifying for lay-people or what.

Hawking (or others, I forget ...) has said that backwards time travel should be possible with "negative energy", which tells me that there are 1st Law issues -- I assume the amount of "negative energy" required is equal to E = mc^2 of the mass being sent back in time, so that mass and energy are conserved.  Which is a pretty huge amount of energy for a people-sized mass.

Assuming sufficient negative energy can be made, and assuming "I promise not to kill my grandfather" allows negative time travel, I think that still creates problems because all of the "stuff" whenever you go there is going to be in the wrong place because you weren't there in the first place.  In other words. you can't take a jump a lake because the "first" time the lake water was there, you weren't in it.  Not only is "stuff" in the wrong place, but so is gravity -- your gravity wasn't part of the universe's gravity.  And so on down the line -- the entire universe has to be changed just so you can tell yourself who won the BCS championship ...

"Obviously I'm convinced of the existence of G-d. I'm equally convinced that Atheists who've led good lives will be in Olam HaBa going "How the heck did I wind up in this place?!?" while Christians who've treated people like dirt will be in some other place asking the exact same question."

luca
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another 3 qsts

FurryCatHerder wrote:

luca wrote:
Quote:
when the wavelength (inverse of frequency) reaches the Plank Length, that's it -- no more increase in energy is possible
Could it really happen? Could the frequency of an electromagnetic wave rise to that point?

I've never read anything which would indicated it would be impossible, though it would be nigh on impossible.  Specifically, since the energy of a photon is inversely proportional to the wavelength, as the wavelength went from two Plank lengths to one Plank length, the energy would have to double.

One practical problem is that a photon with that much energy would exert a huge gravitational attraction on anything anywhere near it, and if it interacts with anything, it would immediately release large numbers of massive particles.

To exert gravity shouldn't the photon have mass? Would Heinsenberg's indetermination ruin the misuration of the frequency? Would Planck's energy get in the middle while rising the frequency?

Vastet
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The most simple, yet

The most simple, yet ironically unvisited, causality problem is microbial. Going back in time even a little while could/would subject oneself to pathogens the body had no defence for. To say nothing of the damage a few viri and bacterium which had evolved to counter an immune system which was effectively suddenly deprived of the ability to similarly evolve defences, not to mention the potential for cross species mutations, and you have some potentially catastrophic problems.

If going back in time is possible, and I believe it isn't possible (I sure as hell hope it isn't), then strict isolation and no interaction is the only way to ensure there is no paradox as a result (though it's possible that even simple observation could affect an unintended consequence).

You don't have to intend a change for a change to propogate exponentially.

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luca wrote:To exert gravity

luca wrote:

To exert gravity shouldn't the photon have mass? Would Heinsenberg's indetermination ruin the misuration of the frequency? Would Planck's energy get in the middle while rising the frequency?

Wow, so many hard questions

Photons do have mass -- E = mc^2, m  = c^2 / E, E is dependent on =frequency=, the higher the frequency, the higher the energy, the higher the equivalent mass.

Energy and mass are interrelated -- you can't talk about one without talking about the other at the same time.

What a photon doesn't have is a rest mass.

I assume you mean "mensuration" -- I couldn't find a definition for "misuration" and at least "mensuration" means something to do with measurement.  Heisenberg only comes into play when we want to measure something.  Otherwise, Nature just keeps on going, whether we measure it or not.

I'm not sure what you're asking with the last question.  My understanding is that wavelength is quantized, but there are still questions about spacetime and whether or not it's quantized.  However, if spacetime is quantized, wavelength is also quantized.  If that's the case, it's impossible to go from 2 to 1 quanta without making the step all in one go.

"Obviously I'm convinced of the existence of G-d. I'm equally convinced that Atheists who've led good lives will be in Olam HaBa going "How the heck did I wind up in this place?!?" while Christians who've treated people like dirt will be in some other place asking the exact same question."