So Zeno’s paradox is real? The speed at which we travel to a very distant location has to exceed the rate of expansion or we will never get there. Nevermind the effect expansion surely must have on GR.
I was making a linguistic point, not a philosophical or scientific one with that sentence. I meant that the idea of speed is included in the idea of non-zero velocity, it is part of the definition of velocity.
Nelson Pike, neither Cornell nor Harvard is measuring the expansion of the Universe in units of velocity. Those are actually units of frequency, though it’s rare to express them as such.
The reply above may actually contain units of linguistic value, but it contains no units of philosophical or scientific value.
I hear on here all the time that anti matter will annihilate matter. Is there any hope or possibility That if the two were introduced that a dis-assembly could happen in some kind of organized fashion that would allow for reassembly at some point, allowing for high speed travel while they were in a non matter state?
Nelson Pike, I’m not sure what you’re saying, there. It looked like you were saying that Cornell and Harvard were not making distinctions between recession speed and expansion rate. But they both were, in that neither one was using speed units for the recession rate, so I was correcting that.
No. And even if it were, that doesn’t get you faster than light travel. It might allow for “travel” at the speed of light. You record the state of the material by some method, send a message containing the state of the material via ordinary photons at c, and make a copy of the material at the other end by some method.
Now, does this actually allow you to travel at the speed of light to Alpha Centauri? Maybe, if you accept that an exact copy of you is actually you. But it’s not faster than light.
The problem with using “non-matter” stuff like tachyons to transmit messages faster than light is, how do you detect the tachyons? How do you create them? The whole point of tachyons is that, if they exist, they don’t interact with normal matter in any way, which means that they might as well not exist.
I don’t understand the question or meaning of “dis-assembly” but the interaction of a normal matter particle and its antimatter counterpart–such as an electron and a positron, or a proton and antiproton–results in the release of pairs high frequency photons (gamma rays) and in the case of baryons or composite bosons reorganization of the remaining constituent quarks into new and often exotic particles that generally rapidly decay into more ordinary stable matter like electrons or neutrinos. In no case do any of the constituents move faster than light except in the restricted sense that quantum interactions can be interpreted as occurring across space-like intervals but only only in a practically non-deterministic sense (e.g. resulting from hidden variables).
None of this gives any practical hope from physics as we understand it for warp drives, “transporters”, traversable wormholes, or other conceits of popular science fiction, all of which would require either abandoning notions of strict local conservation of momentum or allowing for non-smooth or multiply connected manifolds of space-time. There is no particular reason that these assumptions can’t be invalidated by some new principle, but we’ve failed to see any conclusive evidence or mechanisms for overturning those essential postulates.
Stranger
If aliens were found to be able to do ftl travel, that would be evidence, wouldn’t it? But I think it would be evidence for travel between multiple manifolds or something - it is not like the massive evidence we have for not being able to exceed c in our universe would disappear.
Both measure expansion in km per second per Megaparsec. Please explain, carefully for us non-specialists, how that is an expression of frequency rather than velocity.
Now, you are not contesting that the theory of Cosmological Inflation (I guess what you would call the theory originating with Alan Guth) holds that the entire universe expanded faster than the speed of light very soon after the Big Bang, are you? Do Cornell or Harvard contest it? Don’t Cornell and Harvard evaluate the velocity of the expansion somewhere in the links I offered?
I brought the topic up here because I felt it was interesting and relevant to the OP topic of superluminal phenomena. I am sorry to see a reply confining itself to a dubious linguistic correction when there is so much of philosophical and scientific interest to to talk about.
A megaparsec is a distance (as is km, while seconds are a time unit). With regards to units, if something is in units of distance/time divided by distance, the distance units cancel each other and it’s really just 1/time, which is a frequency.
I’m not sure if this is non-specialist enough, without doing half of Physics 101. If there’s anything here confusing, feel free to ask.
I’m not certain what you mean. If aliens originating from somewhere else in our universe were able to traverse a distance of space faster than light could travel along the geodesic path, then it would indeed be evidence for superluminal travel of some sort, and would suggest that our understanding of physics, and specifically relativity is incomplete but not invalid for all normally observed phenomena. If aliens came from someplace outside of our universe, or an alternative universe, or somesuch, it would suggest that there are physical phenomena that are outside of any established models of physics whatsoever, and would put the discussion into the range of exotic cosmology that we’re not equipped to address except by wildly speculative suppositions.
[ul]
[li]kilometer (km): unit of distance : 1000 meter[/li][li]second (s): unit of time : 1 second[/li][li]megaparsec (mpc): unit of distance : 3.08567758×10[SUP]22[/SUP] meters[/li][/ul]
The units of distance cancel out, leaving just units of time[SUP]-1[/SUP], which is by definition frequency.
For a rate of expansion of 100 km/s/mpc = 100 x 1000 m / 1 s / 3.09×10[SUP]22[/SUP] m = 3.24×10[SUP]-18[/SUP]/s = 3.24 attohertz
Stranger
I am contesting that, because the statement makes no sense. It’s like asking whether I contend the statement that my height is greater than ten pounds.
Whoof.
Just to give the units meaning:
x km/s per megaparsec means that the recessional velocity increases by x km/s for every megaparec distance the observed object is away from the observer.
The Hubble parameter expressed in terms of frequency means how many times the distance between objects increases by a factor of e (i.e. the mathematical constant) per unit time due to expansion, if the Hubble parameter were constant (as in a de Sitter Universe)
This probably shows why, despite the Hubble constant/parameter having units of frequency, it is pretty much never treated as a frequency. I.e. what it is actually the frequency of is obscure, unintuitive and not very useful.
Alternately, if you take a model where the recessional velocity between any two objects is constant, the age of the universe is just the reciprocal of the Hubble parameter.
Maybe I’m just odd, but to me that actually makes more intuitive sense as a metric.
Thanks to Quercus and Stranger On A Train for their replies above. They at least tried to educate me.
I wonder where I went wrong. Inflation theory definitely hypothesizes that something underwent superluminal expansion. Maybe the problem lies with the phrase “entire universe”. As far as I can tell from several hours of googling it would have been more accurate (I think) to say that only space expanded faster than the speed of light, carrying matter more slowly along subluminally. Or perhaps I should have said the observable universe.
If there isn’t anything above to satisfy Mr. Chronos’ objections, then I will part with the comment that he might be just a bit too finicky.
This reply must be from a pom-pom girl (masculine first name adopted for identity confidentiality purposes) on the cheerleading squad at the Chronos Institute of Technology . I bet she’s cute when she’s all dolled up in her work tutu.
I think the common misnomer that inflation was “superluminal expansion” is that in an inflationary Universe regions are causally connected that aren’t in the non-inflationary equivalent. I.e. compared to a similar non-inflationary model it “appears” that signals have been able to propagate FTL in an inflationary model.
This is simply because, whilst we still call the region that would be the observable Universe in the non-inflationary equivalent “the observable Universe” when talking about the inflationary model; using the strict definition of “observable Universe”, the observable Universe in the inflationary model is in reality much, much larger.
There is however no real sense I can think of in which it would be correct to say space expanded FTL in inflation. As has been pointed put spatial expansion is measured in units of frequency and superluminal recession velocities within the confines of the observable Universe occur outside the inflationary epoch too.