Ask a physicist anything. (5)

AV1611VET said:

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Absolute zero is 0K

1611AV said:

A star is say 1,000,000,000 light years away. Do we see the light that is 1,000,000,000 light years old?

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Not always. Space is expanding, stars are moving - and if the star is 1 billion years old, it may very well be gone by now

1611AV said:

If the above is true then, have there been any new lights popping up in our sky that say are 1,000,000,010 light years away?

I always see the same pattern of stars. Why?

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Two main reasons:
1) A new star visible to the human eye would probably go unnoticed. Are you telling me you've perfectly memorised every star in the night sky?
2) New stars occur all the time (I think it's 40 per year in our galaxy), but there's no reason why they should be bright enough for us to see. We've been properly observing stars in their details for about 200 years, which is a tiny sliver of time compared to the actual scales of these events - it could be millions of years for a newborn star to go from being inert to actually pumping out enough light to be visible.

So why don't you see new stars? Because you physically can't

Drathnor said:

Do quark nutrinos favor being matter over antimatter?

(Somthing i went to a lecture on )

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Quark neutrinos? Quarks and neutrinos are two different types of fundamental particle, both of which can be either matter or antimatter. You get quarks and antiquarks, neutrinos and antineutrinos.

So, yes, quarks prefer being matter over antimatter because they are matter, and aren't antimatter

But if you're referring to the matter-antimatter discrepancy (and I feel you are ), then, again, the answer is yes - but buggered if anyone knows why!

Exiledoomsayer said:

Not to rush you or anything but if working the sums out is giving that much issues I would settle for the formula that would need to be used to arrive at the answer.

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That's what I'm trying to deduce I have the generation formula, if you want that:

For n dice of sizes a[sub]n[/sub], the generating formula P(x) is given by:



For two dice of sizes a and b respectively, I've partially simplified this to:



I've been busy and computerless for the past few days, so I haven't done much else (not that I did much to start with )! Good luck, young padawan

TerranceL said:

What's the coolest thing you've ever seen in physics?

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I think AV has the right reply

AV1611VET said:

As I understand it, you eventually reach what is called the Planck length -- (1.6162 × 10[sup]-35[/sup] m) -- where you can no longer halve something.

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The Planck length, like the Planck time, is a division of space (and/or time) between which events don't really make sense according to quantum and/or relativistic mechanics. That is, it's the shortest distance, and the smallest amount of time, between which two events can take place - there physically can't be anything that happens between t = 0 and t = 1.1612 x 10[sup]-35[/sup].

Think of it as the fundamental clock tick of the universe.

(I'd use a computer analogy, but I fear the computer nerds would rabidly attack me...)

If you cool a particle to zero degrees Kelvin, it still vibrates. Why and how?

faith guardian said:

If you cool a particle to zero degrees Kelvin, it still vibrates. Why and how?

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How indeed. You can't cool a particle to 0K, because it will always be able to vibrate. If you can cool something to absolute zero, you've broken physics

Wiccan_Child said:

How indeed. You can't cool a particle to 0K, because it will always be able to vibrate. If you can cool something to absolute zero, you've broken physics

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lol

I read about this and saw vibration still exists at 0K.
I was wondering about that. I asked my professor if this might be due to the relationship between matter and energy, but he did not know.

faith guardian said:

lol

I read about this and saw vibration still exists at 0K.
I was wondering about that. I asked my professor if this might be due to the relationship between matter and energy, but he did not know.

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0K is the theoretical limit at which all thermal energy is removed, but that limit is as unachievable as a perfect sphere, for much the same reasons. The nature of matter forbids it.

You can get negative temperature, though

Wiccan_Child said:

0K is the theoretical limit at which all thermal energy is removed, but that limit is as unachievable as a perfect sphere, for much the same reasons. The nature of matter forbids it.

You can get negative temperature, though

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Yes, so I heard. It baffles me a little, I must confess.

I gotta ask, can you show me the math?

faith guardian said:

Yes, so I heard. It baffles me a little, I must confess.

I gotta ask, can you show me the math?

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For negative temperature? Sure. A system with negative temperature (on the Kelvin scale) is one in which sufficient energy has been given to maximise entropy - and then more energy is put in. Most systems will just increase entropy further, but some systems will experience a decrease in entropy as even more energy is pumped in.

So negative temperatures are temperatures that are hotter than hot - energy flows from the negative system into the positive system, because, physically, the former simply has more energy. Or, rather, entropy is raised in both systems by making energy flow out of the negative-temperature system. An example might make things easier.

Consider a system that is made up of 100 pseudo-quantum thermodynamic particles - that is, particles that exist in either a spin-up or a spin-down state - with a magnetic field applied. Thus, the spin-down state is less energetic than the spin-up state, so particles with less energy are 'down', while energetic particles are 'up'

If you cool the system, draining it of energy, less and less particles have sufficient energy to be 'up', so more are 'down'.
Conversely, heat the system, and more particles will have have enough energy to be 'up'.
So, as the system gets hotter, there is more energy to be passed around. So you have absolute zero (all are 'down'), and a sort of scale of ever hotter temperatures as more can flip up and down randomly and freely.

But, what if you put even more energy in? An 'up' particle cannot take any more energy, so this extra energy has to go into those particles which are 'down'.

Eventually, all the particles are 'up'. But that means the system is uniform - more uniform than when there was less energy. So, entropy has decreased as you pushed even more energy in.

That is, the system has a negative temperature.

Read about it in New Scientist and found it bizarre, had the sneaking suspicion it behaved differently because it was another state of matter, but they called it negative temperature.

So with what has been said thus far, we can not half something into nothing and if we could it would be pure energy. Thus, something can never become nothing right? And if that is true then the opposite must also be true. Nothing can never become something.

Which means that everything that makes up the universe has always been. Its eternal with no beginning and no end.

Is that a fair analogy?

1611AV said:

So with what has been said thus far, we can not half something into nothing and if we could it would be pure energy. Thus, something can never become nothing right? And if that is true then the opposite must also be true. Nothing can never become something.

Which means that everything that makes up the universe has always been. Its eternal with no beginning and no end.

Is that a fair analogy?

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No, for a number of reasons.

1. Something can indeed become nothing - matter cancels with antimatter, positive kinetic energy cancels with negative potential energy. Ultimately, it may all balance out.
2. The question about halving is to do with atoms and molecules, physical substances - not the annihilation or creation of matter. That's another matter entirely
3. The phrase "something to nothing" is different to the reverse, "something from nothing". Chopping something in half doesn't remove the parts - it just splits them in two. You can't cut something in half and then make both halves vanish - if you could, we'd never have invented knives
4. "You can't get something from nothing" is a funny old philosophical issue, to which my short retort is, "quantum mechanics begs to differ".
5. The universe isn't a physical object we can cleave - as I said, the fundamental limit arises because of the nature of matter, atoms, protons, quarks, gluons. Space is something else entirely.

So, no, I wouldn't say that's a fair analogy.

Assyrian said:

Read about it in New Scientist and found it bizarre, had the sneaking suspicion it behaved differently because it was another state of matter, but they called it negative temperature.

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It's an annoyingly clever concept

1611AV said:

So with what has been said thus far, we can not half something into nothing and if we could it would be pure energy. Thus, something can never become nothing right? And if that is true then the opposite must also be true. Nothing can never become something.

Which means that everything that makes up the universe has always been. Its eternal with no beginning and no end.

Is that a fair analogy?

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Not really, no.

Virtual particles appear out of nothing. Besides there's three problems:

1) Just because we can't half things into infinity, doesn't mean that we can't make something into nothing.

2) Halving something infinitenly would NEVER yield you nothing.

3) Just because something can never be nothing, doesn't mean that nothing can never be something.

sandwiches said:

Not really, no.

Virtual particles appear out of nothing. Besides there's three problems:

1) Just because we can't half things into infinity, doesn't mean that we can't make something into nothing.

2) Halving something infinitenly would NEVER yield you nothing.

3) Just because something can never be nothing, doesn't mean that nothing can never be something.

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Nothing+Nothing=Nothing 0+0=0 every time. Something can not come from nothing.

1611AV said:

Nothing+Nothing=Nothing 0+0=0 every time. Something can not come from nothing.

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You can say that until you're blue in the face, but like Wiccan said: QM shows otherwise.

sandwiches said:

You can say that until you're blue in the face, but like Wiccan said: QM shows otherwise.

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OK. I'll have to study up on QM tonight

1611AV said:

OK. I'll have to study up on QM tonight

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That's the spirit! Even if you end up not agreeing with what you read, hopefully you'll be a little wiser for it, anyway.

QM is one of those things that says seems to throw "common sense" out of the window. What little I know is very interesting.

1611AV said:

Nothing+Nothing=Nothing 0+0=0 every time. Something can not come from nothing.

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Trite, but, alas, not true. First, there's no evidence that something cannot come from nothing - there is no experiment, no concrete data that even suggest genesis ex nihilo cannot occur. Moreover, there is both theoretic and empirical reasons to believe that things do indeed come into existence ex nihilo.

It has to be said that the primary opponents of this are philosophers (there are philosophers against everything ), and those theists attempting to shoehorn a Creator into being. They simply cannot accept that "something can't come from nothing" is wrong, since that invalidates their whole argument - that God must exist. To them, something can't come from nothing, so there has to be a God from whence everything came. Despite rather glaring theological and philosophical complications in this reasoning, its foundational premise is at best unfounded, and at worst at odds with established science - that some things do indeed come from nothing, without prior cause.

The much-loved intuitions of causality (every event has a cause) and simultaneity (two events are separated by a fixed and unalterable length time) have also taken a beating by science, but that's a topic for another day. Or today. I'm easy

1611AV said:

OK. I'll have to study up on QM tonight

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Like sandwiches said, QM is not friendly to common-sense. Reality is what it is, regardless of those truths are comfortable or even comprehensible.

Wiccan_Child said:

Something can indeed become nothing - matter cancels with antimatter, positive kinetic energy cancels with negative potential energy. Ultimately, it may all balance out.

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An explosion is not a "canceling out" of energy, is it? When matter and antimatter meet, does the energy inherent in both disperse, or does it become nothing?

The question about halving is to do with atoms and molecules, physical substances - not the annihilation or creation of matter. That's another matter entirely

The phrase "something to nothing" is different to the reverse, "something from nothing". Chopping something in half doesn't remove the parts - it just splits them in two. You can't cut something in half and then make both halves vanish - if you could, we'd never have invented knives

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Nature of a Cone

"You can't get something from nothing" is a funny old philosophical issue, to which my short retort is, "quantum mechanics begs to differ".

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You can't get something without the mechanics existing. The mechanics are something.

The universe isn't a physical object we can cleave...

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It should be by now, you guys need to work harder. Quit slacking off.