I don’t know if anyone will be able to offer some help in this or not, but maybe you could point me in the right direction.
Recent calculations indicate that the universe is conitnually expanding. The cause is suspected to be something called “Dark Energy”. The way it works out is that the dark matter has some sort of negative gravity effect and is pushing at the universe causing it to expand. One theory is actually that there are trillions and trillions of tiny explosions in space where matter is continually formed and destroyed, the net effact is stretching the universe, causing it to expand ever more rapidly. There is not enough normal matter in the universe to produce enough gravity to slow down this effect.
Now, there is another theory, this one about near light speed space travel, that says if you take a vessel, and exert a small amount of push to it, without any resistance, the vessel would eventually reach a near light speed velocity.
If you combine these two train of thoughts, then you have dark energy, which is all these tiny explosions, pushing on the universe ever so slightly, so that over billions of years, this energy has got the universe expanding at an ever increasing velocity.
What happens when the velocity of the expanding universe reaches a point where it is near or at the speed of light (Einstein say faster than speed of light is impossible), and what would keep it from continuing to go faster and faster? Does the universe have a terminal velocity? One would not think so since air resistance is needed for the terminal velocity effect to work.
Also, isn’t it possible to figure out how fast the universe is expanding (based on how far away supernovae are when compared to how far away they were say six months ago) and try to use this to figure out how much outward force there is on the universe, and see if that corresponds with the extimated amount of dark energy to help confirm its existence?
They did figure out how fast the universe is expanding based on obesrvations of rthe redshift of extremely distant type I-A supernovae, and calculated the amount of dark energy in the universe from that. Two thirds of the total energy in the universe is dark energy, the rest is normal energy, according to the most recent findings.
yes but does the current speed of the universe, re-worked backwords, correspond with the amount of pressure being exerted?
going back the the near light speed vessel… lets say just for arguments sake that the small amount of push exerted onto the vessel is 10 lbs per square inch… you can use this to calculate and predict how fast the ship will be traveling in say 5 or 10 years, so you must be able to work that in reverse to check your work…
could you not apply the same principal to jthe universe? if you know how fast it is traveling now, and can predict how fast it will go into the futre, can’t you figure out how fast it was traveling in the past? if you could then you could use this to build a model of reverse growth of the entire universe. if you could do that you could use it as a brand new method of calculating the age of the universe. you could also use that to calculate how much matter/energy (be it normal or dark) it would take to make the universe move from inception to where it is now.
I know most of the answers to my questions have been figured out via other means (especially the age of the universe), but this would provide a new and unique perspective, and very well may come up with some surprising results
The current issue of New Scientist has a cover story on dark energy that may answer some of your questions. The pressure exerted is a measure called w. The exact number for w would tell us a lot about what is causing the expansion. We don’t know that yet, so we can’t work backwards from it.
I’m not sure I understand some of what you’re asking, though. Dark energy isn’t a bunch of tiny explosions; it’s a repulsive force. And are you saying that you think the expanding universe would exert a push on an individual vessal? I don’t think that’s true.
And the universe itself can expand faster than the speed of light. That limit applies only to massed particles, not to spacetime. Air resistance doesn’t apply here. It’s simply a balance between forces that will determine whether the universe is contracting or expanding and at what speed.
The OP is not clear on one point: We have known for decades the universe is expanding. Hubble’s red shift and all that. What is “recent” is that the rate of expansion may be increasing.
As to objects that might appear to be receding from us faster than the speed of light. There really are such galaxies. This does not violate relativity since it is the space between them that causes a “virtual” motion. I.e., no “infinite energy” was needed to “speed them up”. (Quotes here denote a simplistic point of view.) Of course we cannot actually observe such objects since their red shift is literally off the scale. The light emitted from them now will never reach us.
Note that looking very far away = looking very far back in time. We also cannot look back in time farther than the Big Bang.
Thirdly, the current rate of expansion is figured out by red shift+distance calculations of far off galaxies. IIRC, the idea that the rate might be changing came from supernova spectra in very old galaxies. The recent calculation mentioned by Q.E.D. was based in part on properties of the microwave background radiation. There is nothing going on at this time scale that can be detected changing over a 6 month period. 6 months out of around 14 billion years is nothing.
the point being ftg is that we are capable of making accurate calculations of the current and future speed of the galaxies (the speed in which galaxies are moving away from each other to be more specific) even if the method i described is flawed…
if we can do this, why can we not work backward and predict the other things i was talking about (age of universe, etc.). you mention 14 billion years, but there are some epxeriments that show stars as old as 16 billion years, so having a third way to determine it may clarify the situation a little…
and my analogy to the space vessel was not to state that the universe itself would be the means of the “push” i was describing. you could have several different ways to acheive this, from a parachute type vessel that relies on light reflected from the sun, to the low enrgy, low output, long running engines that have been proposed.
as far as the whole moving faster than the speed of light thing goes, i could go on for days about that… such as the thought that may prove you cannot “stop time”. since time is an essence of light, in that we can measure time by how long it takes for light to go from its source to our eyes, since we know the speed of light we can calculate how long it was, or the “time”. so to stop time you would also have to stop light, and if you stop light then the universe ceases to exist, if there is no light, then would that not mean that you would forever be stuck there?
Damn- I thought we were going to have a dark energy discussion, not one about wacky propulsion methods…
like you, I could go on all day about weird propulsion methods, but it is only useful to do so in a science fiction context.
still, the dark energy data is still being argued about, even by conventional cosmologists (if such creatures can be said to exist)…
Robert Caldwell of Dartmouth University says that dark energy might be so strong that individual galaxies, planets and even atoms might get ripped apart in 20 billion years.
We’re not capable of doing this yet. Still too many ifs and unknowns. Some predictions have been made, but more than one fit the current information. Again, see the New Scientist article since it touches directly on this.
First, there are dozens of ways to measure the age of the universe. Measurement of the cosmic microwave background now puts it very precisely at 13.7 +/- 0.2 billion years. This is considered to be a real breakthrough in age measurement.
I’m not sure if you could use w as an independent measurement of the universe’s age, either. It looks to me as if w is derived from other measures so it would not yield an independent result. I’d like a physicist to comment on this, though.
Yes, this is a description of space travel. What relation does this have to dark energy or the expansion of the universe? And there is always resistance, the more of it as you go faster because the ship will grow more massive because of relativistic effects.
I’m sorry, but I’m about 99.9% sure that this is gibberish.
wether it be because i do not have enough experience on message boards, or because i cannot accuratly describe what i am trying to say, i find it very odd trying to respond to several different points at once…
so, my question in the begining, to which i should not have applied any analogies to apparently, is this: CAN we determine the reletave speed of the galaxies, perhaps even predict the future speed (since the galazies velocity appears to be increasing based on the red shift theroies), and IF we can, can we then use this to work it out in reverse and predict where the galaxies were some 2 billion, or 5 billion, or 13.7 +/- 0.2 billion years?
if we are able to do this, would the location of the galaxies 13.7 billion years ago using this method, correspond with where the galaxies were predicted to be using other alternative methods?
For some types of motion, working backwards from current knowledge is in no way helpful at all. Look at the planets around Sol. We know their orbits quite well. Working backwards for ~5 billion years or more would not tell us a thing about what the Solar system was like back then. The tiniest uncertainty in measurements (I mean really, really tiny) prevents such calculations from being useful.
Ditto the motions of stars in our galaxy or galaxies in our cluster. Working backwards from current motions of galaxies does not tell us where they were a looong ways back.
Now, Hubble found this interesting red shift thing going on which can most reasonably be explained by an expanding universe. So early attempts at calculating the age of the universe were indeed based on basic distance of galaxies, red-shift plots. Draw a line, get a cosmological constant, you’re done. Your suggested method is part of the basis of how this was done.
Note that figuring out the age of the universe has been quite tricky. Some calculations showed ages younger than 5 billion years, which contradicts our knowledge of our Solar systems development. Others were as high as 20 billion years in order to take into account the presumed ages of stars. That’s a pretty big range. But dating objects a long ways off isn’t easy.
The most recent measurement is only accurate if you believe the model behind it. Not all do. (I think it is “mostly” right.) So in a few years there might be a new “more accurate” measurement of 15 or 12 billion years. And so it goes.
If we assume that things behave in the same manner now, then yes, we can fairly accurately predict the motions of the galaxies. But that may not be a good assumption. The “dark energy” field that you mention in your OP is apparently a newcomer on the cosmic scene: It appears to have “turned on” a few billion years ago, for reasons which nobody can yet explain. Further, in the very first few moments of the Universe, it seems that there was another repulsive field operating, similar to the current dark energy, but insanely stronger and lasting for an insanely short period of time. We don’t know what caused that to turn on or turn off, either. So until we get those figured out, we can’t really say with any confidence whether some other “dark energy” field might turn off or on in the future.
The age of the Universe is now considered to be pretty well measured, at 13.7 gigayears, by the MAP experiment (Microwave Anisotropy Probe: It measured the cosmic microwave background). There are other ways of determining the age of the Universe, and they agree with MAP, but that’s not saying much, since all of those other methods have huge uncertainties. Before the MAP results came in, earlier this year, the best we could say was that the Universe is between 10 and 20 billion years. As for the old stars you mentioned, you’re using outdated information. It used to be believed that some stars were as old as 20 billion years, but newer estimates are all less than the age of the Universe. It looks like the first stars formed within a few hundred million years of the Universe.
And one nitpick, by the way: Q.E.D. writes that
“Normal” is a relative term. About a third of the matter in the Universe does gravitate in a more-or-less normal way, but only a tiny fraction of that is baryonic matter, or matter which gets most of its mass from protons and neutrons. This includes pretty much everything we’re familiar with. Of course, one could make the argument that it’s vacuum energy which is “normal”, and that everything else is the weird stuff.