Ask a physicist anything. (7)

troodon said:

Yeah, precise phrasing is very important when one is talking about this kind of subject matter.

I'll go back to science threads now

Click to expand...

Good idea

Naraoia said:

I find it telling that it's always the single mothers you keep going on about. As if all those women knocked themselves up and left themselves to raise their kids alone. (And what about single fathers, anyway?) It takes two to tango, mister.
.

Click to expand...

Yes.
It isn;t the fault of the kids who we raise to set marriage aside until age 26, abut not sex.

cupid dave said:

Yes.
It isn;t the fault of the kids who we raise to set marriage aside until age 26, abut not sex.

Click to expand...

So sad that you think guys aren't involved.

Oh, and focusing only on telling kids they can't have sex until marriage is a leading cause of teenage pregnancy.

Chalnoth said:

So sad that you think guys aren't involved.

Oh, and focusing only on telling kids they can't have sex until marriage is a leading cause of teenage pregnancy.

Click to expand...

?
Where dod I say guys aren't involved in the social consequences, that half of American families are fatherless?

And of course, not getting married is the root cause of single mothers... which proves we can NOT tell teens to be nuns and priests until age 26.

Rather than invent the issue of what do I think about the causes, look at the problem and be constructive.
We tried Sex Education for 40 years and it failed, so what's next beside silencing me???

cupid dave said:

?
Where dod I say guys aren't involved in the social consequences, that half of American families are fatherless?

Click to expand...

Hey, I'm not the one that is blaming single mothers.

cupid dave said:

And of course, not getting married is the root cause of single mothers... which proves we can NOT tell teens to be nuns and priests until age 26.

Click to expand...

You do realize there is such a thing as divorce, right?

cupid dave said:

Rather than invent the issue of what do I think about the causes, look at the problem and be constructive.
We tried Sex Education for 40 years and it failed, so what's next beside silencing me???

Click to expand...

Stop lying, please. Sexual education, combined with broad access to various forms of birth control, has been proven to be quite effective at reducing teenage pregnancies. Replacing sexual education with abstinence-only education has significantly worsened matters.

We could do even better if we had a proper safety net for the poorest Americans.

Sex education works when people like Rick Perry aren't confusing the issue and claiming that abstinence only works.

Scientific studies show that, among the factors inhibiting even educated parents in a 2 parent home from giving meaningful sex-education to their daughters, socio-cultural and religious factors are the number one issue.

Pressure from groups like the John Birch Society, MOTOREDE, Parents Who Care, Parents Opposed to Sex Education, the Christian Crusade, and Let Freedom Ring
have gotten in the way of the success of sex education. We haven't actually tried teaching sex education without fundamentalists undermining it every step of the way.

Did you know they just calculated Pi out to 10 Trillion Digits?
Japanese calculates pi to 10 trillion digits | Crave - CNET

I have a question for you physicist. Can you elaborate on the theory of inflation, cosmic microwave background radiation, and red shift. How does these 3 effects the big bang. Thanks.

superman2010 said:

I have a question for you physicist. Can you elaborate on the theory of inflation, cosmic microwave background radiation, and red shift. How does these 3 effects the big bang. Thanks.

Click to expand...

The Big Bang theory is the idea that, for the past 13.5 billion years, space has been expanding from something very small to its current size. Despite popular misconceptions to the contrary, it is not yet known whether the start of the Big Bang was the start of the universe.

The theory of inflation is the idea that the initial expansion of space at the start of the Big Bang was faster than the speed of light - space grew faster than light took to cross it. This idea was borne out of observations of the distant universe, and explains why the large-scale structure of the universe is largely homogenous - because space expanded so quickly, there was no time for any heterogenous structure to develop.

The Cosmic Microwave Background Radiation (CMBR) is the triumph of the Big Bang theory. The theory predicts that there should be a background spectrum of light, approximating a black body with a temperature of about 2.3K (-270.85°C, close to absolute zero). When we looked into the black parts of space with the COBE satellite, we were able to measure the background spectrum. This is a graph with both the predicted and measured spectra:



They are exactly the same. Such a close correlation between reality and theory is rare, which is why this is such a triumph for the Big Bang theory.

Red Shift is the phenomenon whereby light is 'stretched' due to the expansion of spacetime. As light gets stretched, its wavelength increases, pushing it towards the red end of the spectrum (hence its name): ultraviolet light becomes blue light, blue becomes red, red becomes infra red, IR becomes microwaves, etc.

But how do we know if the light we detect has actually been stretched, or whether it's unchanged? Well, when light is emitted by (say) a Hydrogen atom, the actual wavelengths emitted are very particular, and form a fingerprint by which we can identify the glowing atom or molecule. So we can identify Hydrogen when we see it. But what we actually saw was that these unique identifiers were all shifted down the spectrum by the same amount - they were 'red shifted'. The amount by which they were shifted also correlated with distance: objects further away were more red-shifted than others. This was the underpinning observation that lead to the Big Bang theory: space has expanded during the light's travel, and it has expanded more for distant objects (since they've travelled longer and experienced more stretching).

Redshift can also be attributed to the movement of the stars and galaxies, and we can work out how fast they're moving. As it turns out, except for local gravitational anomalies, all distant objects are accelerating away from us.

Hope that answers your questions!

superman2010 said:

I have a question for you physicist. Can you elaborate on the theory of inflation, cosmic microwave background radiation, and red shift. How does these 3 effects the big bang. Thanks.

Click to expand...

Haha, wow, that is not a small question. Or rather series of questions. I'll try to be as concise as possible.

First, red shift. As the universe expands, stuff in the universe gets, on average, further away from one another. This also effects light by causing the peaks of the waves to get further apart. So as the universe expands, light beams are expanded by the same factor, and light that has been traveling for longer tends to look redder. We can determine that this has happened because energized atoms tend to emit light in a specific pattern of wavelengths. So when we see the exact same pattern, but each wavelength in the pattern multiplied by the same number, then we know that there has been a redshift.

Now, the cosmic microwave background. From the fact that stuff in our universe that is further away has a larger redshift, we know that things in our universe are moving away from one another and cooling. This means that if you go back into the past, things were closer together and hotter. If you go back far enough, our universe was so hot and so dense that it was a different sort of matter: a plasma. The hydrogen in our Sun, for example, exists in this same kind of plasma state. And one of the defining qualities of a plasma is that light has a hard time getting through it. That is, the Sun may be emitting a lot of light, but you can't see through it: the Sun is opaque. Our early universe was like this as well. It was an opaque plasma. And when it expanded and cooled enough, this plasma cooled to become a gas. Our universe became transparent. So all of the light that was bouncing around in that early plasma state was free to travel through the universe. That light has since been redshifted by a factor of about a thousand, so that we now see it in the microwave range, hence the Cosmic Microwave Background.

As to inflation, well, inflation solves a number of theoretical problems with the basic Big Bang theory. The basic Big Bang theory assumes two things:
1. The universe has stuff in it that is spread out relatively smoothly.
2. General Relativity is correct.

If we make these two assumptions, some very strange contradictions appear. First, the fact that we exist at all seems strange. If you just take the above assumptions seriously, the overwhelming prediction is that either our universe will expand so fast that no galaxies ever form, or it recollapses back on itself in a tiny fraction of a second. Then there's the additional problem that the Cosmic Microwave Background is nearly uniform, but according to this basic Big Bang theory, different parts of the sky that we can see have never communicated before. That is to say, we see one spot on the CMB that is at, say, 2.7262 Kelvin, and another spot in the opposite direction that is at 2.7264 Kelvin (yes, the real differences in temperature are that small). But if the two parts of the universe have never been able to communicate due to the speed of light limitation, how did they become nearly the same temperature?

Inflation, it turns out, solves both of these problems. Inflation proposes a new sort of quantum-mechanical matter that causes a rapid, accelerated expansion in the early universe. This both solves the problem of our universe instantly recollapsing or expanding too fast, and solves the problem of different parts of the universe never having been in contact. And it also leads to a new prediction: not only does it say that everything in our observable universe was once in contact, but the quantum foam during inflation also acts as a seed for the tiny differences in temperature we see in the Cosmic Microwave Background. Crucially, it predicts a very specific statistical signature which we can see clear as day in the real CMB.

It simply does not take a rocket scientist to tell someone that heterosexual intercourse may result in birth and that abstinence or some sort of barrier to conception (such as a condom) reduce the chance of pregnancy.

The problem is a moral problem, a problem of lack of self-control, of rebellion, of irresponsibility, etc. The problem is a practical problem, also, in terms of dealing with peer pressure and impulses/drives and consequences. But the problem is not a primarily intellectual problem.

ToBeInChrist said:

It simply does not take a rocket scientist to tell someone that heterosexual intercourse may result in birth and that abstinence or some sort of barrier to conception (such as a condom) reduce the chance of pregnancy.

The problem is a moral problem, a problem of lack of self-control, of rebellion, of irresponsibility, etc. The problem is a practical problem, also, in terms of dealing with peer pressure and impulses/drives and consequences. But the problem is not a primarily intellectual problem.

Click to expand...

The things society can do to reduce the problem is, however, an intellectual problem. And in practice the things that can be done that we know are effective are:
1. Comprehensive sexual education.
2. Broad access to contraceptives.
3. Improved social safety net.

What we know is not effective is telling people, "That's bad! Don't do it!"

ToBeInChrist said:

It simply does not take a rocket scientist to tell someone that heterosexual intercourse may result in birth and that abstinence or some sort of barrier to conception (such as a condom) reduce the chance of pregnancy.

Click to expand...

Abstinence really is the best contraceptive (the Virgin Mary notwithstanding), but the problem is that humans simply don't want to be abstinent. And when that fails, the 'abstinence only' program will leave them woefully unprepared for actual sex - they won't have, and won't know how to use, condoms, femidoms, spermicide, etc.

ToBeInChrist said:

The problem is a moral problem, a problem of lack of self-control, of rebellion, of irresponsibility, etc. The problem is a practical problem, also, in terms of dealing with peer pressure and impulses/drives and consequences. But the problem is not a primarily intellectual problem.

Click to expand...

You'd be surprised. If people are told by authority figures that condoms don't work, spread STDs, are immoral, etc, then they'll believe that. People are idiots, and must be treated as such.

Wiccan_Child said:

You'd be surprised. If people are told by authority figures that condoms don't work, spread STDs, are immoral, etc, then they'll believe that. People are idiots, and must be treated as such.

Click to expand...

Also, there are a lot of beliefs about birth control methods that are just plain wrong. For example, the pull-out method? Doesn't work.

ToBeInChrist said:

It simply does not take a rocket scientist to tell someone that heterosexual intercourse may result in birth and that abstinence or some sort of barrier to conception (such as a condom) reduce the chance of pregnancy.

The problem is a moral problem, a problem of lack of self-control, of rebellion, of irresponsibility, etc. The problem is a practical problem, also, in terms of dealing with peer pressure and impulses/drives and consequences. But the problem is not a primarily intellectual problem.

Click to expand...

Abstinence is a great option for a number teens and unwed young adults. But for a far greater number, this isn't a realistic solution.

This is a behavioral issue, which, in its simplest terms means a choice made by weighing risk v reward.

We can't stop humans from acting on human impulses completely. But we can help them limit partners, schedule sexual activity around fertility cycles, use of contraceptives AND birth control, utilize touching yourself, ect. to limit pregnancy and disease. But that is only if the decision is well-informed.

Chalnoth said:

Also, there are a lot of beliefs about birth control methods that are just plain wrong. For example, the pull-out method? Doesn't work.

Click to expand...

It's easy to see how the naive might think it would work, though. I read once that people in a neighbourhood in Africa were shown how to use condoms with a cucumber - and they ended up buying cucumbers en masse, putting condoms on them, and then having unprotected sex, thinking they were baby-proof.

What is the coldest temperature a fire could withstand?

Zippy the Wonderslug said:

What is the coldest temperature a fire could withstand?

Click to expand...

I think right now the coldest flame we've found is around 250 °F

Cool Flames and Autoignition in Microgravity

^ Sorry. I meant like in a room/atmosphere.

So say could you light a butane torch in -200 F degree freezer room?

Zippy the Wonderslug said:

^ Sorry. I meant like in a room/atmosphere.

So say could you light a butane torch in -200 F degree freezer room?

Click to expand...

I'd say near 2.7 Kelvin (Temp of Space) and Stars (in space) don't seem to have an issue with flames