SCIENCE (said in a deep, meaningfully spooky voice)

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Jezreel

Re: SCIENCE (said in a deep, meaningfully spooky voice)

Postby Jezreel » Wed Aug 28, 2013 5:44 pm

SO if we go fast enough we won't age much?

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RB
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Re: SCIENCE (said in a deep, meaningfully spooky voice)

Postby RB » Wed Aug 28, 2013 6:01 pm

In relation to how time passes here on earth but your cells will still replicate badly at the same rate so if you travel at near light speed for ten years, you'll still be ten years older.
A slight majority of a statistically worthless sample size agree.

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Re: SCIENCE (said in a deep, meaningfully spooky voice)

Postby Polito45 » Wed Aug 28, 2013 6:02 pm

Jezreel wrote:SO if we go fast enough we won't age much?


If you can get to 67 million miles per hour you won't age at all.
Time will have effectively stopped for you.

I believe this can be observed directly in the Large Hardon Colluder.
Sub-atomic particles that "live" for a certain amount of time "survive" for longer the faster they are accelerated.

So, it is the case, isn't it? That the faster you travel through the spacial dimensions the slower you travel through the time dimension?

RB wrote:In relation to how time passes here on earth but your cells will still replicate badly at the same rate so if you travel at near light speed for ten years, you'll still be ten years older.


True, but when you slow down and stop you will be in the far future - you can just grow a new body in a jar.
Or, just buy a jar of blackcurrant jam, some scones and then head back.

:mrgreen:

EDIT: Actually, I don't think that's right. - If you could immediately accelerate to light speed, travel in a wide loop back to your starting point and stop.
You would not have aged at all. The people you left behind however would be long gone. Tinlad knows how much time would have passed - it would depend on the length of your journey but I'm guessing it's a lot.
"It is the mark of an educated mind to be able to entertain a thought without accepting it." — Aristotle

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Re: SCIENCE (said in a deep, meaningfully spooky voice)

Postby Mr.Clark » Wed Aug 28, 2013 10:24 pm

Ok, this is just me throwing ideas out to see what sticks.

Is it because everything has an effect on spacetime? The larger the mass, the larger the warping of spacetime, right? (which is why planets have more gravity than people). However, the faster you travel, the greater your effective mass (relativistic mass?) which is why you can never travel faster than c (speed increases, mass increases, energy required to accelerate you increases even faster, as c^2 is a ridiculously big number).

But if your mass is increasing, so is your effect on spacetime... in this case, noticed by the fact that the faster you go (and the more you warp spacetime), your time relative to an observer is travelling slower.


Or am I just a crazy person?

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Re: SCIENCE (said in a deep, meaningfully spooky voice)

Postby Polito45 » Wed Aug 28, 2013 11:18 pm

Total nutjob. ;)

Sounds good to me but I'm just a Padawan in theoretical physics, Tinlad seems to have mastered the force. :ugeek:

My understanding is that as you say, matter particles gain mass with velocity so as they near C (67 million mph) you need a truly huge amount
of energy to push them faster, but to push them past C you would need an infinite amount, therefore it's not possible.
BUT, photons (the force carrying particle for the electromagnetic force) have no mass.
So it would seem that a particle's mass is not the only thing that stops it exceeding C. :?

Something I was taught years ago as a kind of mental aid was to imagine the 3 spacial dimensions - up/down, left/right & forwards/backwards.
Add to this the time dimension which is intimately attached to the 3 spacial dimensions and here you have ALL of the universe.
With a single coordinate from each of the above I can describe any place and time in the entire universe since it began.

And it's a closed system. The more you go in one direction, the less you go in the opposite and other directions.
Sounds really stupid because it's so obvious but imagine if for example you're moving forward, you're not just drawing in the backwards,
you're also drawing in the up/down and the left/right as you go faster AND because the time dimension is intimately attached,
you're drawing that in as well. When you've drawn in all of the other dimensions as far as they can go including time - i.e., when you've reached C.
Then there is nowhere else to go. You are going as fast at you possibly can in this closed system.
"It is the mark of an educated mind to be able to entertain a thought without accepting it." — Aristotle

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Re: SCIENCE (said in a deep, meaningfully spooky voice)

Postby Mr.Clark » Thu Aug 29, 2013 8:28 am

Then how do tachyons go faster than light? (It has something to do with them not being able to slow down below c, but it breaks your model a bit... ;) )

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Re: SCIENCE (said in a deep, meaningfully spooky voice)

Postby Tinlad » Thu Aug 29, 2013 11:53 am

Mr.Clark wrote:Then how do tachyons go faster than light? (It has something to do with them not being able to slow down below c, but it breaks your model a bit... ;) )

They can achieve it by being purely hypothetical. ;)
Polito45 wrote:Tinlad seems to have mastered the force. :ugeek:

I did literally master it (MSci Physics with Theoretical Astrophysics)... but that was three years ago, and since then I've been working out how to make better dog treats. A lot of Newtonian mechanics, but not so much relativity. So it's been great fun dragging this knowledge back to the front of my mind!

I just need more time to be able to sit and try and answer some of these questions! :)

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Re: SCIENCE (said in a deep, meaningfully spooky voice)

Postby Polito45 » Thu Aug 29, 2013 1:47 pm

Tinlad wrote:... I've been working out how to make better dog treats. A lot of Newtonian mechanics but not so much relativity.


You're attempting to create the perfect dog treat for throwing at your dog's face? - cool. 8)

Tinlad wrote:I just need more time to be able to sit and try and answer some of these questions! :)


But we're running out of time man! Think of the children!!!
Quick! How big is the universe?

:mrgreen:
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Re: SCIENCE (said in a deep, meaningfully spooky voice)

Postby Mr.Clark » Thu Aug 29, 2013 6:29 pm

Tinlad wrote:
Mr.Clark wrote:Then how do tachyons go faster than light? (It has something to do with them not being able to slow down below c, but it breaks your model a bit... ;) )

They can achieve it by being purely hypothetical. ;)

Well yes. But even hypothetically they have to fit in the existing framework (or come up with a new one that explains all current observations as well as how the new hypothesis fits)

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Re: SCIENCE (said in a deep, meaningfully spooky voice)

Postby Tinlad » Mon Sep 02, 2013 1:09 pm

I've never really looked at the theory, but based on 5 minutes Googling:

The tachyon is a result of taking quantum field theory and saying "what if there was a field with imaginary (in the mathematical sense) mass?". There is no evidence that such a field exists, but the neat thing about theoretical physics is that there's nothing to stop you plugging any numbers you like into the existing equations to see what you get out. :D

It seemed to be that, if you worked it though, a quantum field with imaginary mass would give rise to particles that travel faster than the speed of light. That would cause all sorts of issues with causality. However, work since then has shown that if you apply a bit more rigour, you don't end up with super-luminal particles: a quantum field with imaginary mass in fact represents an instability in which (regular, positive mass) particles can be spontaneously created (tachyon condensation).

Unfortunately, the former interpretation is a lot more sexy than the latter, and so the idea of super-luminal tachyons persists.

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Re: SCIENCE (said in a deep, meaningfully spooky voice)

Postby Polito45 » Mon Sep 02, 2013 7:46 pm

You are like a God to me. :D

I was reading last night about how string theory tames the quantum foam by positing the Planck length as a limit for the size of
fundamental sub-atomic particles and so enabling quantum mechanics and general relativity to be used together without spitting out infinities.

They seem to be saying that because you can't probe below this length - because there is literally nothing to probe with, and so it might as well not exist.
What are your thoughts on this oh mighty one?
"It is the mark of an educated mind to be able to entertain a thought without accepting it." — Aristotle

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Re: SCIENCE (said in a deep, meaningfully spooky voice)

Postby Tinlad » Mon Sep 02, 2013 10:06 pm

The Planck length is an interesting one - it's the length you get if you combine three other constants: the speed of light, the gravitational constant and the Planck constant.

There's nothing intrinsically significant about it, but there are clues that it's a really important scale for trying to tie together various areas of physics - particularly, as you've noted, quantum mechanics and general relativity.

Example:

There is something called the Compton wavelength. This is the wavelength λ at which a photon has the same energy as a particle of mass m:

λ = ℏ / mc

where ℏ is the reduced Planck constant and c is the speed of light. The Compton wavelength has a physical significance in that it's the shortest wavelength photon that can be used to measure the position of a particle accurately: a short wavelength must be used to create an accurate measurement, but as you use shorter wavelength photons their energy increases... and once this energy exceeds the energy of the particle you're trying to measure, you run the risk of creating another identical particle when making your measurement - and ruining it! When you get to this minimum wavelength, you're squarely in quantum mechanical territory.

Now, to a different area of physics.

There's a concept called the Schwarzschild radius. If a mass m is compressed to the Schwarzschild radius r, its gravitational escape velocity reaches the speed of light (for a non-rotating black hole this the event horizon). The radius is approximately*:

r = Gm / c^2

where G is the gravitational constant. Once you reach this scale, you're very much in the realm of general relativity.

OK. So what?

Both the Compton wavelength and the Schwarzschild radius are measures of length. At what point does λ = r? If we set:

ℏ / mc = Gm / c^2

and solve for m we get:

m = sqrt(ℏc / G)

And if we put this mass into either the Compton wavelength equation or the Schwarzschild radius equation we get a length:

l = sqrt(ℏG / c^3) = 1.6e-35 metres

The Planck length! So when we get down to this scale, it would seem that both quantum mechanics and general relativity are having important effects. So yes, any theory (string theory, quantum gravity, etc.) working on this scale has to incorporate quantum mechanics and GR neatly without any nasty infinities or division by zero. Interesting, huh? :geek:

* it's approximate because it ignores a factor of two: when doing this type of calculation we're just interested in orders of magnitude, and so it's very common to just ignore numerical factors.

Jezreel

Re: SCIENCE (said in a deep, meaningfully spooky voice)

Postby Jezreel » Mon Sep 02, 2013 10:13 pm

ALien glyphs.

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Re: SCIENCE (said in a deep, meaningfully spooky voice)

Postby Polito45 » Tue Sep 03, 2013 12:03 am

^^
:D

I read somewhere that if you scaled up the size of the earth to the size of the observable universe,
the planck length would be about the size of an average tree. :shock:
Aren't we talking about scales so infinitesimal that we will never, ever be in a position to probe them?

Another quick question - What shape is the universe?
"It is the mark of an educated mind to be able to entertain a thought without accepting it." — Aristotle

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Re: SCIENCE (said in a deep, meaningfully spooky voice)

Postby Tinlad » Tue Sep 03, 2013 1:39 pm

A quick answer - almost certainly flat.

A longer answer:
When talking about the shape of the universe, we're generally talking about whether spacetime is curved when we look at it on a large scale. The way to test this is to use Pythagoras!

Let's use the Earth as an analogy. Draw a small triangle on the ground and measure its internal angles: they add up to 180 degrees, as we've known for over 2000 years.

Now draw a bigger triangle, and repeat. And a bigger one. And a bigger one.

Now let's draw a truly colossal triangle. Use the equator as the baseline, draw a line down from the North Pole along the prime meridian, and another along the 90th meridian to form a continent-scale triangle. Now sum up the angles. 270 degrees! Pythagoras is broken!

This is because the underlying surface (the Earth) isn't flat - it's curved.

If we scale it up suitably, we can use the same experiment to test whether spacetime is flat or curved too. But that's kinda tricky. Luckily it turns out that you can use other observations to work it out. You can take measurements of the cosmic microwave background and a few other bits and pieces, do some maths, and work out the value of the density parameter, Ω.

If Ω = 1, the universe is flat, and Pythagoras holds.
If Ω > 1, the universe has positive curvature and spacetime is curved like the surface of a ball (this is the Earth example; angles sum to > 180 degrees).
If Ω < 1, the universe has negative curvature and spacetime is curved like a saddle (angles sum to < 180 degrees).

NASA's WMAP probe has so far determined that, to within 0.4% error, Ω = 1 and therefore the universe is flat.

Oblig. Wikipedia image:
Image


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