Betelgeuse, Betelgeuse, Betelgeuse... may be getting closer to Supernova...

Re: Betelgeuse... I was hoping you were gonna show up Bra... I'm glad you did.

Well, sure. Anything's possible. But my point was just that it's only massive (and luminous) stars that go supernova and only nearby stars that could have any effect. A nearby, luminous star is going to be pretty damn bright since it fulfills both the criteria for something appearing bright: that it's nearby and putting out a lot of light. That's not going to be missed.

V838 is cool because we see light echos lighting up the expanding shells of gas around it. That gives us some idea how big these shells are (since we know the speed of light). The result: they're damn big. This is really interesting because mass loss is one of the primary things that dictates the uncertainty in high-mass stellar evolution. Studying this star will give us ideas of where our models need to be tweaked.

The point is the radiation pressure from one of these supernovae is going to be really weak by the time it gets to the solar system. And the shock wave from the SN is never going to reach us. So, while Earth can (and does) get bombarded by high-energy photons, they aren't enough to affect the orbits of Oort cloud objects. Moreover, you need to remember that our solar system is TINY compared to the distance between stars. This means that most of the energy of one of these supernova blast waves is just going to pass on either side of us; it's going to be WAY spread out by the time it gets to us and we're only going to occupy a TINY angle of the expanding sphere.

And I'm actually pretty unusual, too.

It's more than a guess. It's a physics-based model to try to understand what goes on in stars. We have plenty of examples of supernovae that have been measured (although it's been a while since one has gone off in the Milky Way; we're actually overdue), so we do have some idea of the energy constraints. And we can also compare ensembles of stars to these models and, depending if we've done it correctly, it's either going to match or not. We actually have the stellar evolution models ~95% there. It's just that this final stage of evolution, particularly of high-mass stars, is not totally understood. We've actually made some pretty big leaps in the last 10 years or so.

There's no way to know if this star has gone supernova yet. Nothing can travel faster than the speed of light, so we'll only know postfacto if this star went supernova now (or 500 years ago, or whatever). The point is that what we're observing now happened 600 years ago.

 

Based upon my understanding of Einstein and special relativity, I must side with Daniel. Whether or not it has already happened is a matter of reference frame and convention. And for many event pairs, there is no unique answer about which event was first and which came after. Even when it is 600 light years away, Daniel can very easily define a reference frame where it does not pop until the moment we observe it to pop.

When we can measure the observation time of some astronomical events to tiny fractions of a second (T=2009.41234567891 +/- 0.0000000003), but don't know the distance to better than a few hundred lightyears, I find it bizarre that we back-date the time 600 years (T=1400 +/- 200). This represents a horrible loss of accuracy, and converts the time to a variable that will change with every updated distance estimate.

Therefore I prefer the convention that the nova happens at the moment we observe it, at the specified observation location.

 

Fuzzy beat me to it, but I'll say it again in my own words:

The problem with the above paragraph is that the word "now" defines a specific time only in combination with the word "here." There is no meaning to "now" in some other place.

Let's say we observe the explosion of Betelgeuse tomorrow. We could then say that the explosion took place 640 years ago in our frame of reference. But there will be other frames of reference within which I typed this post before Betelgeuse exploded. Those frames of reference will be moving very near the speed of light with respect to our frame of reference, but since Einstein told us there is no absolute frame of reference, we cannot say one is "right" and the other is "wrong." We can only say that one is ours and the other is not.

Within our frame of reference, Betelgeuse may have already exploded. But that is a very limited and subjective view. Two events can only be ordered in time if a light beam from one can reach the other. And this is not the case with my typing this post and the explosion of Betelgeuse, unless the light is in the sky now and I'm just not looking in the right direction to see it.

I am not speaking of Schrodinger's Cat: the idea that an event has not occurred until it is observed. I am speaking of Relativity physics, which describes a counter-intuitive relationship between space and time, or more precisely unites space and time into a single concept of space-time, and rejects the Newtonian idea of an absolute frame of reference and an absolute and universal time.

 

"Frame of reference" I have the same problem if I drink too much

 

I'm not sure you guys are right. Even if two events have a space-like separation, can't we just talk about simultaneity in our frame? In other words, can't we just say that the explosion happened in 1400 AD (in our frame), even if we don't get that information until today (in our frame)?

It's been a while since I took GR and I don't use it in my everyday life, so I'm not sure about this. . .

EDIT: I think you guys are basically saying this same thing in your above posts. Perhaps I was just imprecise in my earlier wording.

 

If a star explodes in the universe, and there's no one there to hear it...

But...but...isn't there still a 'big R Reality' that just IS, independent of our feeble attempts to comprehend it? Outside of our own little worlds, we don't create reality, we just try to figure it out. Reality isn't affected or effected by what we think it is.

Hopefully the cat doesn't run out of lives before we 'unscrute' the inscrutable.

Isn't spacetime still a continuum, with a 'before', a 'now', and a 'not yet'? Isn't it always 'now', no matter where you are? Can things be observed before they happen?

Well, one thing's for sure. There's no quicker way to make people's heads explode than to start discussing theoretical physics. I think I'll go back to doing income taxes.

 

The problem is that there really really is no such thing as simultaneity. It's an illusion arising from our limited experience: We never experience things that are really fast or gravitational fields that are really strong.

"Before" and "after" only have real meaning when separations are time-like, not when they are space-like.

But yes, as long as you specify that you are speaking from our frame of reference, you can put a date on the explosion if you know the distance, once you've observed it, and as long as it is understood that you are speaking from a very subjective point of view.

Note that from the frame of reference of the light itself, the events are "simultaneous." I.e. no time passes in the photon's frame of reference between its emission and its absorption, and there is no distance between the two events. From its own point of view it has traveled zero distance in zero time.

There is a Reality. But time and space are not separate things. There is a clear mathematical relationship between them, it's just not the one our intuition wants us to think.

Spacetime is a continuum. Events whose separation is "time-like" have a definite order. But events whose separation is "time-like" are in a different order depending on the frame of reference from which they are considered. The actual separation between events is expressed in mathematics that most of us never bother to study, and therefore seems to the common mind to be nonsensical. But it's actually our intuitive view of time that is nonsensical.

Things cannot be observed before they happen. Things can only be observed when the separation between the event and the observation of the event is time-like, in which case there is a definite order, a before and after. But many event pairs (where the separation is space-like) cannot observe each other.

I cannot observe the explosion of Betelgeuse until the light from that explosion reaches me.

There is no Absolute frame of reference. All frames of reference are subjective. But Relativity provides the relationship between all frames of reference. That relationship is Real and quantifiable, if you care to learn the math.

 

You sure about this? Isn't the speed of light constant in all inertial frames? Wouldn't this imply that there is some time that must elapse for the photon to traverse space?

Or maybe you're just trying to evaluate the equations for Lorentz contraction and time dilation at their limits?

 

According to us, light travels at 300,000 km per second. But according to the photon, the speed of light is infinite?

"Relativity is absolute" was always one of my favourite tshirt slogans.

The other is "War is peace, freedom is slavery, ignorance is strength, time is money"

 

It is indeed because of the dilation of time and space. At the speed of light, both contract to zero.

The speed of light is the same in all frames of reference. But since both contract to zero for the photon, as mentioned above, the photon does not violate the speed of light because it travels zero distance in zero time.

All very counter-intuitive.

It's very hard to get your head around the idea that an object that for us is 640 light years away, is right here in the frame of reference of a photon that moves from there to here. A clock riding on the photon would measure zero time for the trip that our clock measures at 640 years. And a yardstick riding on the photon would measure the distance as zero. That's probably why it took so long for anybody to figure it out.

 

Entanglement is a "possible" property in quantum mechanics. Quantum mechanics and relativity are not at present reconcilable, but each is very well established in its own realm: Relativity for the very large and the very fast; quantum mechanics for the very small. When a unified field theory is finally worked out, it will necessarily reconcile the present incompatibilities. I suspect it will do so in a manner that does not alter the fundamental principles of either. How will it manage that? If I could answer that I'd probably win the Nobel Prize for physics.

 

SPF 25,000.

Tom

 

A simple way to think of this is to put yourself in the photon's shoes. As an object's speed approaches the speed of light, time dilates and distance contracts. Since photos move at the speed of light, they are at the limit: time stops and distance shrinks to zero. From its reference, a photon is created and destroyed simultaneously, without traveling any distance. From another reference frame, the same photon may live for thousands of years and travel thousands of light-years.

Photons are able to travel at the speed of light because they have zero rest mass. All objects become more massive as they approach the speed of light. At the speed of light, any non-zero rest mass object would be infinitely massive, therefor requiring infinite energy to accelerate it to that speed. Since photos have zero rest mass, they don't have this little problem.

Tom

 

So time changes speed, too?

(Married people don't really live longer. It just feels that way.) :croc:

 

But you've got a "frame" issue there. The "length" of the photon (whatever that means) only contracts to zero in the frame of a stationary observer. Moreover, I think you have the time dilation thing backwards. As you approach the speed of light, the time dilation grows large (i.e. since sqrt(1 - v^2/c^2 is in the denominator), so it takes infinite time, but again, this is only as measured in an inertial frame.

This is the standard "falling into a black hole" experience. As you fall towards the black hole, an outside observer will see time slow down for you. For yourself, however, you have a completely "normal" experience in your frame. If you had a watch on, you'd see it ticking away as always.

 

But this contraction/dilation does not happen in the frame of the photon; only in the frame of an outside observer in an inertial frame.

We're agreed there.

 

Yes.

A photon has a wavelength. I'm not sure how that relates to the "size" of an object with mass. The photon has no rest mass and no size at rest, so perhaps the contraction of space does not affect its "size." Perhaps wavelength and size are not comparable things. I'm not even sure an electron has a size, other than its wavelength, which contracts as it speeds up. (Higher energy = shorter wavelength.) An atom or a molecule has size, only because there is separation between the particles that make it up

And the trip does not take infinite time. From our point of view it takes finite time. From the photon's own point of view its trip took zero time, but since space contracted to zero, it traveled zero distance and the speed of light is not violated even for the photon itself.

You always see your own watch ticking because your perception operates in the same time frame as your watch. But note that here, the slowing of time is due to the intense gravitational field, not to high speed of the object with relation to the observer. There are relativistic effects, but I think they are different. A near-light-speed trip across the galaxy is reversible: you can turn around and come back, even though a lot of time will have passed back home. The trip into the black hole is not reversible: you can never come back out. Energy can "evaporate" from a black hole by quantum effects, but information cannot. Therefore a really small black hole can disappear, but the object that fell into it is gone forever.

(Parenthetical useless and irrelevant side note: My sister came up with the idea of black cat hair holes, and I submitted an article on them to the magazine of the Griffith Park Observatory in L.A. My article was rejected. The difference between black cat hair holes and regular black holes is that if you fall into a black hole you will be crushed out of existence, whereas if you fall into a black cat hair hole, the cat hair will cushion your fall and you will be gently crushed out of existence.)

As you increase in speed, things ahead of you and behind you become closer, but your clock shifts as well, to preserve the speed of light constant. Therefore, if you had a space ship capable of traveling close to the speed of light, you could cross the galaxy in a few minutes. It would appear to you that as you approached the speed of light the galaxy itself was contracting in your direction of motion, so that you would have only traveled a few miles, by your own yardstick. A couple of hundred thousand years would have passed on earth by the time you got back, but for you, hardly more time would have passed than the time you spent there and the time it took you to accelerate and decelerate.

Furthermore, if you shined a light ahead of you, the photons would appear to you to travel away from you at the speed of light, though an observer sitting on a planet you passed would see them moving away from you, and would see you practically keeping up with them. Of course, that observer would have to have a very fast camera because you'd go by so quick.