Astronomy hangups - Knowledge vs. comprehension

dicktice · 2002-12-04 20:47:21

Some aspects of astronomy and cosmology just don't seem comprehensible to me, in spite of the knowledge obtained from available textbooks and journals. I mean gut-wise, not analytically as presented and proved mathematically. Here are a few "astronomy hangups" of mine, which I need help with.

Photons (1): Electromagnetic spectral "quanta" having no mass, capable of impinging physical mass at the "speed of light" to impart momentum. I know they do so on light sails, but isn't there a gut explaination as to how massless quanta exert force on inertial mass?

Photons (2): Emitted by luminous objects in space, they are capable of forming images on sensititive (CCD) arrays without distortion from any distance, in spite of having taken up to billions of years to arrive in the case of most distant observable objects. My gut interpretation of this is that, since they propagate at the "speed of light," to a photon regardless of frequency (energy), distance has no meaning and therefore no time exists for distortions to intervene. But I can't find anything in the literature that deals with astronomical image sharpness in terms of the medium (photons).

Photons (3): Images received of astronomical objects represent them at the instant of photon emission. Objects at distances requiring enough billions of years, at the "speed of light," for their emissions to arrive representing them less than a billion years (say) after the Big Bang...would seem to require the universe to have expanded faster initially than the speed at which the image propagated. I suspect that relativistic effects must be involved, but nothing I've read gives me the gut understanding of what's really happening.

Are there any other members with such hangups out there...and other, enlightened ones, able and willing to clear them up?

soph · 2002-12-04 21:08:58

Well, for number 1, doesnt gravity do exactly that? It's a force with no mass, yet it exerts a pull on mass. its hard to understand quite how it works-only that it does.

i have a "hangup" with the wormhole theories. if they existed, as sagan said, as black holes, how could we use them to travel through? as soon as you passed through the center, even assuming you could do this, you would be sucked right back to the center by gravity. thus, there is no way of exploiting the wormhole to shorten travel, in my understanding.

Phobos · 2002-12-04 21:55:19

Photons (2): Emitted by luminous objects in space, they are capable of forming images on sensititive (CCD) arrays without distortion from any distance, in spite of having taken up to billions of years to arrive in the case of most distant observable objects. My gut interpretation of this is that, since they propagate at the "speed of light," to a photon regardless of frequency (energy), distance has no meaning and therefore no time exists for distortions to intervene. But I can't find anything in the literature that deals with astronomical image sharpness in terms of the medium (photons).

Could you explain further what you mean when you say the light doesn't arrive distorted? I can think of an image being distorted from it's original form due to things like the influence of gravity on the light before it reaches the ccd, but I think that's not the type of thing your talking about. Anyways, about the relativity thing, for us the observers, we would be able to observe possible distortions because we don't exist in "frozen time" like the light itself does. It would take infinity for the light to realize it has been messed with somehow but not for us. I'm not sure though if were both on the same page.

Shaun Barrett · 2002-12-05 02:06:17

Dicktice, I think with subjects like relativity and, especially, quantum mechanics, a "gut understanding" is nigh on impossible to achieve.
A gut understanding is really only possible within the framework of our day-to-day experience. For instance, at the kind of speeds humans are used to, there is absolutely no reason to suspect that an object is going to gain mass as it moves faster. According to relativity, though, it does. Intuition can't help you with this concept - you just have to trust the mathematics.
I don't know about you, but I have trouble visualising what time actually is. I know it 'passes' and I can broadly estimate it's passage ... i.e. I can judge the 'length' of an hour. But as to what it actually is ... ! So, when Einstein tells me time goes slower for me when I move faster relative to an observer, there's really no way to grasp such a thought. If you can't really visualise what time is, how can you visualise it being stretched or compressed? It's back to the mathematics again for an intellectual understanding only - because at the gut level, it doesn't make sense. ???

I'm not sure if you're aware we discussed the fact that light can impart momentum to solid objects right here in "Science and Technology" (? ).
Look up "Humans and relativity, Could they take it?" for the explanation of how it's assumed to work.

As for your second point, photons can be regarded as discreet packets of energy which do not attenuate with distance - i.e. they don't lose their energy as they travel. They're immortal if you like!! So there's no way they can distort with distance unless acted upon by something in their path, like gravity. Gravity can and does change the path of light (witness gravity lensing). And, naturally, interstellar dust clouds can and do absorb photons - and perhaps re-radiate them in a different direction and at a different wavelength.
Am I helping, or am I barking up the wrong tree?!

Your third point may be explained by 'inflation'. Theorists have concluded that soon after the big bang there was a period of super-rapid expansion of the universe, called inflation. The whole fabric of space/time suddenly ballooned out much faster than light speed, separating much of the matter in the universe by distances impossible to explain otherwise.
Apparently this theory has become well established and fits the known facts very well. I don't pretend to understand all the details but it may help to answer your question (? ).

dicktice · 2002-12-06 12:56:05

Thanks, Shaun. I shall dig into the sources you mention. I never, ever even heard of "inflation theory" wrt the Big Bang aftermath. You'd think they would at least mention it in the texts that devote so much space on the "looking back into time" theme! Any suggestion(s) as to source for hangup No 3? If not, thanks again for the time spent on Nos 1 and 2.

dicktice · 2002-12-06 13:20:04

Soph. Regarding gravity, my gut feeling is based upon the two dimensional, rubber membrane analogue which dimples to depths proportional to the mass of objects placed on it. Attraction by larger objects for smaller ones depends upon distance, along a line between, with no vectoring capability.
What I desire is more along the quantum line of thinking. I'm still getting over the shock of learning that the solar wind isn't the basis of "solar sailing," which could have been avoided by using the term "light sailing" in the first place. And then, when the "plasma sail" was described as capable of using the solar wind, but without vectoring being possible....
Thanks for your response. Hope this topic of "hangups" leads to others coming out of the gut-feeling-fix closet.

soph · 2002-12-06 14:07:43

right, the mat. but the only difference is that things always fall towards the larger object, they never orbit it for an extended period of time, even when rolled slowly and from a distance. why doesnt this happen in space? the pull of the other celestial objects?

Shaun Barrett · 2002-12-07 01:28:23

Dicktice, in response to your request, I've located an article called "Inflation for Beginners".

They may describe it as 'for beginners', but (and this may be a clue as to my intellectual status! ) many of the explanations they give still have me scratching my head!!

If you're like me, I think the best bet is to take on board the bits you can comprehend and just try to accept the parts that don't quite make sense.
The point is that some regions of the universe are farther apart than they ought to be unless inflation took place. And inflation is not only inferred from this, it's actually predicted by a particular solution of Einstein's relativity equations (and by the mathematics involved in much more recent Grand Unified Theories.)
This to me is incredible!
In 1917, a guy called Willem de Sitter, using Einstein's general relativity equations, actually produced a mathematical model describing inflation ... before the big bang was even thought of!! It was so out of context in the cosmological world of 1917 that nobody knew what to do with it. So they just nodded, smiled, and put it on the shelf!

So, Dicktice, at least one guy had the answer to your problem about 85 years before you asked the question!

AltToWar · 2002-12-07 10:06:13

A photon has no "Rest Mass."

Rest Mass is a mesurement of an objects mass at 0 speed.

According to Reletivity, as an object gains speed, it gains mass. As an object moves closer towards the speed of light, it takes more and more energy to accelerate the mass. It would take an infinate amount of energey to move a non-mass-less object to the speed of light.

Photons can never move at a speed less than the speed of light. Mass cannot be propeled to the speed of light. therefore photons cannot have any rest-mass.

While photons do not have mass, they do have Angular momentum.

When a photon hits somthing, it energy is either deflected or absorbed.

It is the angular momentum that is transferred.

the direction of light is often deflected by gravity and particles.

Space is very very very empty. So light that travels for billions of years might not encounter any objects or gravity fields.

soph · 2002-12-07 10:46:05

so photons were created by immense nuclear explosions, already at the speed of light, and never slowed down since?

PaganToris · 2002-12-08 13:22:11

I know alot bout space i am a Junor in HS but belive me i know my share of space

dicktice · 2002-12-08 16:45:21

Soph: t
That's easy. It's because there is no roling friction to slow 'em down in space.

Shaun:
Incredible indeed. But before I delve into what I shall call "pre-relativity" where c is not the limiting velocity, why don't cosmology references mention inflation within the context of the Big Bang theory, expecially prior to distance-is-proportional-to-the-past? I'll get back to you, but I wish to describe a light-sailing rig your earlier post got me thinking about (see Interplanetary Transportation).

AlToWar (that's hard to type):
I'll respond point for point, not to act smart, but to try and get you to explain further.
A photon has no mass, period.
0 speed has no meaning in relativity.
None-mass-less objects is a cute term. But what's your point?
By angular momentum, is that due to spin? (Pls see below)
Reflected (not deflected) and/or absorbed?
Transfering angular momentum from a mass-less spinning(?) object would seem to be a contradiction in terms...but this may be where my hangup lies. Could you be more descriptive, please?
Photons diverted (not deflected) by gravity fields, and what kinds of particles (by reflection).
Space isn't empty, but it sure is transparent to lots of the electromagnetic "photons" including photons of light. My hangup is about "traveling for billions of years" (to us) taking "no time" (to photons) because of what you didn't mention in the first place, time shrinking to zero at light-speed.
If you could expound further on the "mass-less angular momentum transfer of photon energy to impart force to an opaque object...." And come to think of it, even frequency- or energy-wise according to whether it's infrared, visible, X-ray...since the material we use may want to be selectively transparent or opaque according to need. Great stuff!

Shaun Barrett · 2002-12-08 18:35:21

Hi AltToWar!

Are you sure you meant to say "angular" momentum?

AltToWar · 2002-12-08 23:19:20

The problem here is that your using 2 definitions of mass.

there is einsteins famous equation of:

e=mc^2

and from it you can get:

m = E / c2

This is an outdated eation though. Scientists today prefer to measure mass as "rest mass"

m = E_0 / c^2

where E_0 is the objects total energy at rest.

Using the more modern equation, the definition of energy can be explained as:

E^2 = m^2 c^4 + p^2 c^2

where p is momentum.

In this equation one does not need to have mass to actually have energy.

What this means is scientists prefer to measure the mass of an object at rest in relation to the observer.

The reason being that as objects approach the speed of light, they gain in mass.

If you measure the mass of a hydrogen atom when it has been cooled to absolute zero, and measure the mass of a hydrogen atom moving at 99.99999% the speed of light, you will get 2 different results.

If one wants to define an absolute mass, you must view it at rest to get consistent mesurements.

The trouble is a photon can never be at rest. One can never observe a photon at rest in relation to their own speed. If you had somthing you thought was a photon, and suddenly stopped it, it would siese to be a photon.

So by the modern definition, photons are attributed with 0 absolute mass.

It's more a bit of mathematics then common sense. The modern standard of mass excludes light on a technicality

If your looking for a more common sense idea about how to understand why a photon exerts pressure on a solar sail, i suggest the following.

If an object with mass and momentum, say a pool cue, came across another stationary object, say an 8-ball, and hit it; the pool cue would transfer some of it's momentum to the 8-ball.

Now a photon is a special particle because it has momentum and energy, but seemingly no mass.

The important thing to remember is that mass and energy are essentially the same thing.

So imagine the pool cue moving towards the 8-ball. On it's way, you somehow magicly removed the atoms of the cue, but left in place the momentum and energy the cue had posessed. The energy would continue as before and strike the 8-ball sending it along.

dicktice · 2002-12-09 17:30:42

AltToWar: Nice try, appreciate the attempt to explain photons exerting force, but I wish you hadn't brought "magic" into it. But, don't delete for a while, I haven't print capability at this terminal...will get back to you when I've upgraded my physics theory regarding magic (oops, sorry, just kidding). I think you're a good sport, and besides, light (my preferred term) sails work. When I have a gut feeling about it, I'll be back to describe how I got it.

AltToWar · 2002-12-10 03:49:44

The point is, it's a flaw in the termenology.

Energy and mass are the same thing.

When someone says photons have no mass, it's according to a scale that does not take into account photons.

It's not the fact that one solid hits another that causes changes in momentum, its a transfer of energy.

My belief is that you cannot remove the real world common sense idea that to transfer momentum somthing hard has to hit somthing else that is hard.

All that needs to take place is energy from one source transferred to another.

If you can seperate out the energy from the idea about solids, perhaps you can grok it.

dicktice · 2003-01-04 13:42:50

AltToWar: I really appreciate the photon discussion. Now, for my next hang-up regarding "the photon": If sunlight imparts thrust to a perfectly reflecting light-sail, normal to the radiation, so that total reflection back sunward occurs, where does the energy to produce thrust come from? I know I'm overlooking something, but it beats me how to explain this. (I'll repeat this to you privately, as well.) ???

Echus_Chasma · 2003-01-04 17:16:25

i have a "hangup" with the wormhole theories. if they existed, as sagan said, as black holes, how could we use them to travel through? as soon as you passed through the center, even assuming you could do this, you would be sucked right back to the center by gravity. thus, there is no way of exploiting the wormhole to shorten travel, in my understanding.

From what I have heard about the difference between wormholes and blackholes is that a blackhole has a singularity (whatever one of those is.) Where as A wormhole is two blackholes where the tube sorta things have joined together before either have formed singularities.

That explaination does'nt do it justice, I don't even know if thats right or not, I just saw it on some TV programme about blackholes.

soph · 2003-01-04 20:27:34

From what i've seen, a wormhole uses the supergravity of a black hole, which compresses space around it, to shoot through a huge area. the problem is, how does a ship survive and escape this gravity field?

Josh Cryer · 2003-01-05 07:16:00

I read that if the blackhole was big enough, you could travel down its center without being ripped apart... dunno how, though.

Palomar · 2003-01-05 09:02:53

I read that if the blackhole was big enough, you could travel down its center without being ripped apart... dunno how, though.

*Like the center of a cyclone or eye of a hurricane, huh? Interesting.

Black holes give me the willies...goose bumps, literally. Eeek!

--Cindy

Josh Cryer · 2003-04-12 23:05:13

Took my 3.5 inch telescope out tonight. The lights near here made it nearly impossible to see faint stuff. I couldn't really pick out Mars in the sky (I never really made an effort to look up where it'd be, I was out there for another reason).

I observed the moon for maybe 4 hours, just contemplating how close the thing is, and how far we've actually come in that regard. I can't believe we don't already have a base there! It's so damn frustrating!

Later, I had a look at a few pinpoints of light. So far away, it really blows the mind. I remember when I was a kid, I would lay on top of my shed/clubhouse and just stare off into infinity, wondering.

My telescope isn't really anything to brag about. Heck, I paid only $10 for it at a resale store. I'm not much of an astronomer anymore, when I was a kid I was much more in to it. Once the internet came out, I found that I could learn more about the cosmos than outside observing could ever give me. But... the internet doesn't give you the kind of feeling that sitting out under the stars does. Ahh, I miss the country life, and my small refractor telescope and binoculars.

I keep meaning to buy some really high powered binoculars (I used to frequent the #astronomy channel no EFnet, and someone pointed me to a rather cheap pair I could probably afford- if they're still available). Maybe I should save up for a good telescope (at least "10). During my time in #astronomy, I was taught how to build my own. It would be interesting to give it a try. Too bad I don't have a nice plot of land out in the middle of nowhere.

Anyway, just wanted to muse. This is really the only astronomy related topic, so yeah. Better to reply here than make my own topic.

dicktice · 2003-04-13 10:22:01

Josh: Reminds me of my 3-inch refracter, made from optics ordered from the (then) Edmund Surplus Company for $10, which I housed in a linoleum tube that sagged at either end, giving an oval field of view. I "discovered" the crescent Venus wasn't Vega with it, and a lot of inverted neighborhood activities over ten blocks away....

Palomar · 2003-04-13 10:22:41

During my time in #astronomy, I was taught how to build my own. It would be interesting to give it a try.

*I read some material about building one's own telescope and how to grind mirrors (for reflecting telescopes) when I was a teenager. I thought if I had the wherewithal to do it, I would have given it a shot. An uncle of mine was a "jack of all trades" sort of fellow, very dependable and extremely intelligent...I think Uncle Chuck would have been happy to help. Unfortunately I didn't have the money to realize the project and my parents were not willing to fund something which they thought was sure to go wrong if I handled it myself (my uncle lived a few hundred miles away; obviously he wouldn't be able to oversee my efforts very frequently).

It's really interesting to check into. Edmund Scientific used to sell "how-to" books in this regard; of course, the last time I checked into it was 20+ years ago.

If you decide to undertake the project, I'd be interested to read how it develops. Like many women, I'm not inclined to "work shop" stuff...but you've reminded me of that hankering from long ago. It'd be a really fun challenge, I think.

--Cindy

Josh Cryer · 2003-04-13 21:36:42

Hehehe, Cindy.

I could never grind my own mirror, I was just thinking of buying my own mirror and placing it within a wooden Dobsonian-style casing. But I did some searching tonight and found that, realistically, it might be better to get one already assembled.

Unassembled I'd save about $250 on a 10 inch scope, but then I'd have to figure out how to construct the tube, etc. Not sure if I'm really up to that. And if it took me more than a work week to figure out (ie, 40 hours thinking it over, constructing theoreitical mounts, etc), I would've been able to pay for the $250 tube and accessories.

Am I making sense?

It might be interesting, though, to simply buy a 6" mirror, and mount it in my 3.4 inch scope. I believe the tube itself is about 6" across. Hmm... nope, just measured it, it's 5" across. Interesting how a 3.5" mirror is mounted in a 5" tube. Maybe I could get a mirror upgrade (a 5" mirror is about $50), though I'd probably have a hard time finding the proper focal length.

What kind of scope do you have, Cindy?

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#1 2002-12-04 20:47:21

Re: Astronomy hangups - Knowledge vs. comprehension

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Re: Astronomy hangups - Knowledge vs. comprehension

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Re: Astronomy hangups - Knowledge vs. comprehension

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Re: Astronomy hangups - Knowledge vs. comprehension

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Re: Astronomy hangups - Knowledge vs. comprehension

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Re: Astronomy hangups - Knowledge vs. comprehension

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Re: Astronomy hangups - Knowledge vs. comprehension

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Re: Astronomy hangups - Knowledge vs. comprehension

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Re: Astronomy hangups - Knowledge vs. comprehension

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Re: Astronomy hangups - Knowledge vs. comprehension

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Re: Astronomy hangups - Knowledge vs. comprehension

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Re: Astronomy hangups - Knowledge vs. comprehension

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Re: Astronomy hangups - Knowledge vs. comprehension

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Re: Astronomy hangups - Knowledge vs. comprehension

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Re: Astronomy hangups - Knowledge vs. comprehension

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