Black Holes, Light speed, and Time Travel

[Jedo the Jedi]

Today in Physics class, we had a discussion about light speed and time travel. It came up that objects moving at a faster rate age slower than objects moving at a slower rate. For examle, a person running is aging slower than a person standing still. Of course, in this case, it's on a very small scale. The same is true of a person riding in an airplane and a person on the ground.

Apparently, all of this is true because that, if you have a watch on, it enters into whatever "time zone" you are traveling in and the time therefore slows. Something like that. Thus, the person traveling at 600 mph in the airplane is moving slower through time than the person on the ground going 0 mph. Get it?

All this talk of slower time at higher rates of velocity led to the subject of space travel and light speed. When someone goes up in a rocket, time slows and they age less quickly. The same is true of when you approach light speed. Hence, if a person were to travel at light speed, they would age slower because of their incredible rate of speed.

We then stumbled upon the subject of distances shrinking when at light speed because light speed becomes the constant. This is where some questions came up. If the distances are "shrinking" you get there faster, right? Also, if you traveled at light speed for say one hour (from your perspective) and you came back to earth, it would almost be as if you had traveled into the future, right? So, theoretically, time travel is possible, into the future anyway.

But what if you taveled backwards at light speed? If you were to go backwards at light speed, then, theoretically, you would be catching the light particles coming off of somebody doing something, and eventually you would catch up to light particles coming off somebody that did something in the past. Wouldn't that be traveling into the past?

Just some thoughts I had, and questions I wanted answered. I have some questions about the nature of Black Holes and dark matter too, but I figured that this was enough for now.

[mudbuck]

You can't actually travel backwards in space, nor forwards. There is no specific directions in space, just locations from one point to another.

The reason why time goes slower for objects in motion exponentially is because existance.exe has a lot of lag time when dealing with ridiculous speeds. The speed of light is actually the program designer's way to prevent the program from crashing.

Oh, and if you do try this someday, don't. A single particle would penetrate a hole the size of your house at those speeds.

If anyone ever sees the computer that runs existance.exe, please don't push Crtl+Alt+Delete
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[Samadhi]

Time dilation has nothing to do with your watch. You could be a naked pigmy or even just a muon traveling at .99C and time would still appear to move slower for you than for the outside world. I'll leave the explanation to someone more versed than me.

Also, you can't travel at a negative velocity. And you can't ever catch light. No matter how fast you go (unless it's the speed of light) it will always be moving away from you at the speed of light.
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[Courk]

You can travel at a negative velocity. You just can't travel at a negative speed.

[Samadhi]

Meh. I'll just stay out of this.
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[extro...]

[Phil_The_Rodent]

You can see into the past anytime you like.

look up

[Jedo]

[mathgrant]

I don't believe in time dilation. It's too complicated.
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[Chuck]

There are no black holes. They're a mathematical placeholder until we figure out what's really going on.

[Celt]

[Samadhi]

[Aarondalf]

Lol, anyone else think Jedo's initial post has all the workings of a spectacularly crappy science fiction novel?

Samadhi, you think its hard to UPLOAD the formula? Try deriving that shit.

[Samadhi]

Oh hell no. I read Einstein's "Relativity: The Special and the General Theory." The note below the title was "A simple explanation that anyone can understand" or something like that. Riiiiiiiiight. I got it, but I had to keep rereading and going back. It's a tough notion to get your mind around.
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[Aarondalf]

The real pain is that once you actually know the equations, to actually get anything practical out of it you have to know a heap of complex physics that doesnt even relate to relativity.

[Jedo the Jedi]

[Chuck]

We don't know what happens when matter is concentrated to extremely high densities. All we have are theories based on the physical laws that we've observed locally. We don't even know if we have all the forces of nature accounted for yet. There appear to be some very dense objects out there but that doesn't mean that light can't escape from them or that they have infinitely dense singularities at their cores.

Anyway, since time slows in gravitational fields it would take an infinite amount of time for a black hole to form. Even if they are possible, there aren't any yet.

[Leptonn]

Aarondalf,

And if you think Special Relativity is hard, take a stab at General Relativity... I have found that you can see (algebraically) most of the well-known SR experiments that have been done (flying atomic clocks in 747s, decay time of a high-velocity particle, etc).

Jedo,

The derivation is a bit finicky, but it isn't hard to show that the energy required to boost a particle from zero velocity to the velocity of light exactly will require an infinite amount of energy. The SR spacetime metric is symmetric, though, so a particle (or spaceship) that somehow started out travelling faster than the velocity of light would require an infinite amount of energy to slow down to the velocity of light. Don't get your hopes up, though - searches for these so-called tachyons have thus far come up empty.

The first experimental evidence (in a law court, it would be circumstantial) for black holes has just come in during the last few years. Astronomers have detected white dwarf stars that are orbiting around something with a mass larger than the Chandrasekhar Mass, in other words, something that should have collapsed in on itself to become a black hole, if our theory is right. Other astronomers believe that supermassive black holes lie in the center of some galaxies. These black holes are believed to be the source of extremely high-energy radiation that might be emitted by matter spiralling into the hole. Borodog's PhD was on a similar phenomenon involving neutron stars, which are collapsed stars that are slightly below the Chandrasekhar limit.

However, Chuck is right. There is no viable physical theory to explain what happens at the center of a black hole. Einstein's General Relativity gives what we have come to call a singularity - a point with something like infinite mass - if the black hole doesn't rotate. A rotating black hole may give rise to a ring-shaped singularity. Some people hope that Superstring Theory (aka M-Theory) will eventually tell us, since it combines the force of gravity, which seems to deal well with large masses, and quantum mechanics, which seems to deal well with tiny distances.

Dark Matter is a highly-speculative theory to describe why galaxies rotate in the way that they do. If you look at a spiral galaxy, the apparent mass in it (including black holes) isn't enough to make it rotate the way it does. Astronomers thus suggest that most of the mass in the universe is dark - in other words, it doesn't interact with matter except through the force of gravity.

Dark Energy is a ridiculously speculative theory that has only come up in the last few years. Observations of giant galaxies from a couple billion years after the universe's apparent formation (Big Bang?) show that the universe is expanding much faster than it used to be. The galaxies are far enough away that the light from them has been travelling most of the age of the universe. The expansion of the universe is like a loaf of bread rising - it's not really expanding *into* anything, it's just getting larger as seen from someone on the inside. Now, the speed at which these galaxies are moving away from us tells us the speed of the expansion of the universe, but by the same token, it's hard to tell exactly how fast the buggers are moving away. In any case, the point may be moot because the results that the dark energy theorem rests on are extremely uncertain.

Hopefully this has been helpful.

[One Skunk Todd]

How can they tell that the rate of expansion has changed?

[Samadhi]

Super novas appear dimmer than they should.

Leptonn: Is this dark energy you're talking about the same as the 'vacuum energy' as it were?
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[One Skunk Todd]

Samadhi, is there a more detailed, yet still lay, explanation than that?

[Samadhi]

Probably.
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[Lucky Wizard]

I actually did a report on the accelerating universe theory once; though I don't have it on hand, I do remember a good portion of the theory, and looking things up online just now has helped me fill in some things I couldn't remember.

There are two types of supernovas; there is the better-known kind where a supergiant star's life ends with an explosion, and another kind that occurs when a white dwarf star's gravitational attraction causes matter from another star close at hand to separate from the other star and build up onto the white dwarf until the white dwarf gets so massive that it collapses. The latter kind -- called Type Ia -- happens to have a predictable luminosity, and we can distinguish these two kinds by their spectrum. Hence, by examining the apparent brightness of these supernovae, we can compare how bright it appears with how bright it is, which tells us how much the light has diffused and therefore how far away it is.

But of course, there are other ways to measure distance. We can determine the speed of the object; since space is expanding uniformly, the rate at which the objects run away from us tells us how far we are from the object in question, since if they're closer they'll move away at a slower speed; this is because the uniformness of the expansion indicates that the distance it moves is proportional to the distance it already is from us. This redshift measurement, of course, assumes that the rate of expansion has not changed; if in fact the rate of expansion was slower once, then it'll be moving slower than its distance would suggest, because the light left it a long time ago when the expansion rate was slower.

So we have two ways to measure the distance of a type Ia supernova. A few years back several teams, including a Harvard team that announced the discovery, compared the two measurements and discovered something odd. Namely, the two distance measurements do not line up; the supernovas were moving slower when the light was given off than the distance (as measured by the supernova's brightness) would suggest if the rate of expansion had never changed. This, of course, suggests that the rate of expansion was slower once, but is now faster.

Hope that helps.

[Leptonn]

Samadhi,

Dark energy is vacuum energy. There's still no real conception exactly what the stuff is, though... Some people think of it as Einstein's Cosmological Constant, Lambda:

G _nu,mu = 8 * pi * G * Lambda * T _nu,mu

(that's the Einstein gravity tensor equation, btw... G _nu,mu is the force of gravity while T _nu,mu is the geometry of space and time)

[Samadhi]

Figured you were probably talking about the same thing, I just hadn't heard it referred to as that.
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[Leptonn]

(Colloquialism of catchphrase) = constant * (amount of funding received)

[tinman]

Experiments here on Earth have already proved you can travel faster than light. You have to relize we do not no everything yet. If you look into Quantem Mechanix youll get an idea of another view of science. Light travels all kind different speeds depending where you are in Glax.....comunication and travel is by rope pull tecnology. Experiment take a pencil slowly pull it across table. It went faster than light.

Proff: If a Lazer beam was same lenghth as pencil and you pulled it and pencil at same time and speed the pencil would move faster.....because the tip of Lazer bean would have a lag time before moving of 186000 mps. Hence rope pull tecnoligy beat out light. Its done using Aeighter in real space travel.
tinman

[tinman]

Just keep in mind people on Earth at this time are only equiped with Victorean Science and most have not seen Hyper Demensional effects in play. We had two huricanes that opned up 5 th demension and had hyper caracter eyes this year, Prof: Remember hurican that stalled of your Florida....for 42 min, then went from level 3 to level 4........I went to weather got photos of the Hyper Mate in eye by working backward I got to photos of weather channel of hyper eyes with the Quantem Mec 3 d effects at work. Have same now. Its so subtle to normal person they did not no what it was.
Just keep open mind to facts that you are not fully aware of the sciences that are avalible yet. There are multiple demensions....to avoid G force the whole ship is transformed encluding pilot into Photon state.......so 90 degree flight caracterists are possible. Another speeds are 100"s thousands times faster than light. For ships....in Galaxy. Why Hyper weather now...we are passing through a flux field in the Galaxy youll see some real different things, as those huricane eyes. Just wanted to check in thanks for the time keep mind open with it you can go anywhere just have to no how......tinman

[Travis]

Finally, someone who knows what they're talking about. Thanks, tinman.

[Vader]

Interesting views tinman. Granted I am just a curious person when it omes to "real" science, I don't pretend to know even a little of the stuff that i should. i remeber the basic stuff that i learned from grammar through high scholl and that is it. I just find it interesting.
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[MTGAP]

[MTGAP]

[Zag]

I've always had a question about this whole "Time is slower for the guy moving" issue. Is it really about acceleration? Because, after all, motion is relative. If I fly out at about a light year away from Earth, then turn back and accelerate towards Earth so that my velocity is 0.9 c and shut off my engines, then I'm an inertial reference frame just as good as Earth is. In other words, from my point of view, I'm stationary and Earth is moving by me at 0.9 c. So do I see all the clocks on Earth as running slower than mine?

[MTGAP]

[Lepton]

Yep, Zag, if you accept that time dilation exists, then both people will see it. The "twin paradox" goes something like this:

[MTGAP]

[Lepton*]

[MNOWAX]

*head starts to swell and blows into a million pieces*
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[MTGAP]

[Amb]

Isn't it useful to know some scientists now believe the speed of light itself can accelerate and slow down....