Discussion in 'Science & Technology' started by The Imp, May 4, 2010.
Ok, that makes sense. Thanks!
Are gluons in hadrons all the time or just some of the time?
As I understand it, gluons are what keep quarks together, and since hadrons are only specific combinations of quarks (or anti-quarks), gluons would have to be there all the time.
Massive disclaimer: I am not a physicist by any worthwhile description of the term.
Gluons are bosons, aren't they? They're the things that carry the strong force, which holds the hadrons together. They have to be there in the same way that you need constant electromagnetic force to hold two magnets together.
They're the strong force-carriers, yes. I believe that's why they're even called gluons.
The electromagnetic force is constant, but I'm pretty sure the photons come and go, so to say.
Well, even if the photons come and go, presumably they are constantly being replaced in order to carry the EM force in the first place?
I'm afraid I'm going to talk myself into a corner if I go on speculating lol
Anyway, not to offend you or anything, but I think I'd like an answer from someone who really knows
Does anyone really know what goes on at the subatomic level? #philosophyofphysics
All the time. The gluons make up about one third of a protons energy. Without them, the protons would be much lighter.
The equations are all there and verified. Solving them is extremely hard, however.
I have a physics question and I'm not sure how to get started to do the math. If you give me the equations I can probably do it myself, but I need some help getting started.
- There is a spaceship flying from point A to point B, the distance between them is d. It is assumed that this distance is light years, possibly between solar systems, but not necessarily.
- It accelerates at a constant rate for exactly half of the trip and decelerates for the second half at the exact same rate.
- The ship has a super amazing shield on the front and back that is able to absorb anything that can get in the way that can't be planned around ahead of time. So basically we don't have to worry about this in this scenario.
- Questions of propulsion type feasibility wrt acceleration (a) value can be ignored as well, unless the acceleration of a ship at the rate runs into any problems with any physical laws in some way. For the last question assume that the only limit is physics.
- The mass of the spaceship doesn't matter, but I realize that it plays a part in the equations. Assume that it's a variable that I can plug in as well. If a value has to be assumed for the explanation, assume that it weighs 10 times as much as a Dragon capsule so 40,000 kg or so.
- If there are people on-board you can assume that they will be safe no matter what the acceleration is due to future technology 58 shielding them from the effects
1. How do I figure out how long the trip will take for values of distance d and acceleration a?
a. from the point of view of observers in solar systems A or B
b. from the point of view of observers on the moving ship
2. What maximum acceleration value a would be realistic given our current understanding of physics, if you assume an unlimited budget for a project to make it happen? If the only limit is physics, given what we know today, how fast can we make something accelerate? I looked here and 3 600 000 m/s² is double of a handgun and gives you a link to ultracentrifuges, which I think are tiny things, but either way that ball park seems like a good starting point maybe? A jellyfish stinger can accelerate at 53 000 000 m/s², is that a reasonable number? Or are these crazy numbers?
3. Are there any limits in the laws of physics for how fast you can accelerate something? Assuming that things getting in the way are not a problem.
Distance = average velocity x time : average velocity = distance / time
Velocity max = acceleration x time x 1/2 = velocity average x 2
Velocity average = acceleration x time x 1/4
Acceleration x time x 1/4 = distance / time
time squared = distance x 4 / acceleration
time = 2 times the square root of d/a
But during very high speeds time passage works differently depending on your frame of reference, won't I need an equation per frame of reference? i.e. somebody on Earth and somebody on the ship
I wasn't actually being serious, but I suppose that the whole point of the Uncertainty Principle is that we can't know for certain what is going on everywhere or even at the same time. We can certainly know to a high probability using said equations, but we're still essentially working on a purely mathematical model.
This page has the formulas you're looking for. Two or three pages down.
I got no answers for these questions, but I guess when you accelerate something so fast that it turns into neutrons, I think you reached your limit
The largest somewhat realistic acceleration for a spacecraft I have heard about were 200 000 m/s^2 for a tiny spaceship with a huge solar sail that is being pushed by lasers. But that only works as long as you are in the range of the lasers. The trick to fast space-travel is not a large one-time acceleration value, but to be able to maintain that acceleration. If you could maintain just 10 m/s^2 forever, you could cross the whole known universe in 100 years of proper time of the spacecraft. In earth's time you are obviously limited by the speed of light, so it would take tens of billion years until that spacecraft would be back (to an earth that might be non-existent by then). The Wikipedia article on proper acceleration has a nice graph that shows what would be possible with 10 m/s^2 (it also contains the necessary formulas):
I do not think there are fundamental limits to (proper) acceleration. If you apply a very large force to a very tiny mass, you can get huge accelerations. More relevant would be practical limits (at which point would the force just destroy the vessel).
That is one interpretation of the Uncertainty Principle. Another is, that it limits to what extent reality is defined. So we cannot know what "really" is going on, because there is no "really" below that level. And so far, we do not know which of these interpretations is true.
Which is coming round to another interpretation of...
I have a physics question, and it may sound silly ... but it has bothered me for a long time, so here goes
As we all know, looking further into space, we also look back in time. When we look and see the Sun for instance, we don't see the star at its actual position, but rather where it was 8 minutes ago. In the case of distant stars, we are seeing them in the positions they were tens or hundreds or thousands of years ago - or even more.
Now, imagine if we had a telescope, a really really large one, in -say- the year 8000, 10.000 light years away from the Earth. The light it will be receiving from Earth it would be from 10.000 years before it went at its position. So, what if it had lens so large, that it could see at the Earth's surface from that distance? Could it see the past? Would something like that even be theoretically possible ?
Yes, but you then have the thorny issue of getting the telescope over there (at least) twice as fast as the speed of light.
That, plus being able to see the sort of detail you want would require an absolutely enormous telescope.
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