IM Egdall

There is no "room for it to expand". There is no edge of the universe. Sounds crazy, I know. But this is what our current understanding tell us.

The four-dimensional approach to special relativity (3 space plus one time) did not originally come from Einstein. It came from his math professor, Herman Minkowski. It is based on the so-called spacetime interval; a certain combination of the space and time intervals. In special relativity, both time and space are "relative". That is the space interval (distance) and time interval between two events are affected by motion. But the spacetime interval is not. Inthis sense, it is absolute. It is the same value, no matter what the relative uniform motion of the observer. Einstein later adopted the four-dimensional spacetime to general relativity. Here the spacetime interval represents how the presence of mass (e.g. the Earth) warps both space and time or warps spacetime. This warping of spacetime is what we call gravity. It tells objects in its vicinity how to move.

I think it has to do with the fact that light has zero mass. Any particle with zero mass (e.g. gluons, gravitons, photons) travels at the speed of light; and always at that speed. So complete time and space dilation occur at the speed which massless particles travel. Also time and space are connected by the spacetime interval (the square root of the difference between the square of the space interval and the square of the time interval). The spacetime interval is absolute. Unlike the space and time interval, the spacetime interval is unaffected by uniform motion. And for particles traveling at the speed of light through space; the spacetime interval is zero. Also the velocity of any object traveling through space and time (spacetime) is the speed of light. So all particles travel through spacetime at the speed of light. The particular value for the speed of light depends on the units used, so it is an arbitrary number. But the "speed of light" is intimately connected with mass and spacetime. Hope this helps.

Per general relativioty and modern cosmolgy models, there is no "outside" outside of space. The universe is expanding, but it is not expanding into anything.

OK, so waht is "negative" mass? Is there any evidence for it? Or is it just theoretical?

What do you mean by "undetermined" particles" in your brain?

Yes. You can express length in conventional length units (like meters) or in time units (like seconds). This is done simply by using the (constant) speed of light, as you have done. So a distance of one meter is also a distance of 3e-9 seconds. Same is true for time. A time of one second is also a time of 299,792,458 meters.

A momentous achievement. I feel lucky to be living in such exciting times.

Universe by Roger A. Freedman and William J. Kaufmann III

YA, but the speed of light is not relative to its context of emission; it's always the same (in vacuum). Or am I missing something here?

Humans have been around for what, about 200,000 years. If consciousness creates reality, does this mean that the universe did not exist before there were humans? What about the 13.7 or so billion years that our universe has existed before humans arrived on Earth? And what if human beings go extinct? Does the entire universe then cease to exist? I don't buy this consciousness creates reality stuff. Oh, and the unified field theory was an attempt by Einstein to unite Maxwell's electromagnetism theory and general relativity. He failed to do this.

I did what you said, and it works. Thanks for the info.

Another dumb blog question from a new blogger. How do I find out how many people clicked on my blog so far? Please advise.

This is the world of relativity. It doesn't make sense because it violates our "common sense". But common sense is a result of our experiences. And we only experience speeds which are a tiny fraction of the speed of light. (Even at airplane speeds, we are only going at about a millionth the speed of light relative to the ground.) At these speeds, relativity effects are so small that they we don't notice them. But they are real, as demonstated in thousands of observations and experiments. So our limited life experience forms how we think about time and space, and limits our perception of reality. Here's another mind-bending prediction of special relativity. Say you are moving with respect to me. And I see two events occuring at the exact same time. In other words they are simultaneous to me. But due to your relative motion, you see these same two events happening at different times! Check it out at: http://www.marksmodernphysics.com/ (Click on selected animations, The Relativity of Simultaneity)

Interestingly, we do experience time travel into the future all the time. It's just at our everyday speeds, the effect is so small we don't notice it. But iti s real. See:

More time dilation data: http://galileoandeinstein.physics.virginia.edu/lectures/srelwhat.html Kaivola, M., et al., Phys. Rev. Lett. 54, 255 (1985) http://physics.technion.ac.il/~jammia/LabV/RedShift2.ppt#267,1,Harvard, Jefferson Tower. (The original manuscript is Pound and Rebka (Phys. Rev. Lett. 3, 439 (1959)) http://articles.adsabs.harvard.edu/full/1979ApJ...234L.219R Clifford M. Will, Was Einstein Right, Putting General Relativity to the Test, Basic Books, New York, 1986) pp. 57 - 63 http://www-astronomy.mps.ohio-state.edu/~pogge/Ast162/Unit5/gps.html http://www-astronomy.mps.ohio-state.edu/~pogge/Ast162/Unit5/gps.html

In our current understanding of the universe (based on general relativity), there is no center of the universe. Where did the big bang happen? It happened here, there, and everywhere. It happened on the tip of your nose. It happened at the star most distant from us. That's why physicists use the balloon analolgy to try and picture this. The SURFACE of an expanding balloon represents our universe. And there is no center to the surface of this balloon. The origin of the surface, where it started expanding, is all places on the surface. And no matter where your are located on the balloon surface, you see the rest of the surface moving away from you. This is all to say that space itself expanded from the big bang. Stange stuff, and hard to comprehend (at least for me), but this is what modern cosmolgy is telling us.

I think the "Universe Created from Nothing" idea is based on: - observations which tell us the universe is "flat", in other words it has overall net zero space time curvature (Cosmic Microwave Background etc.) - general relativity, which says that in a flat universe the total gravitational energy (negative) is cancelled out by the total non-gravitational mass/energy from stars, cosmic dust, dark matter, dark energy etc. (positive). - Thus the net energy of the universe is zero. I objected to this in an earlier post because it seemed to me that this only applies to the VISIBLE universe, that is the part of the universe we can see. (We cannot see the rest of the universe which is so far away that its light has not had time to reach us.) In addition, per inflation theory we observe a flat universe because the entire universe underwent an exponential expansion very shortly after the big bang (By entire universe I mean the observable and unobservable universe.) So our observable universe is a flat region within a most likely highly curved entire universe. So the "universe from nothing" idea is suspect. I asked these questions in an e-mail to physicist Lawrence Krauss. He said "you are correct that our observable universe is flat, and we cannot say more than the local grav. energy in our observable universe is zero." So I thought I had made a good point. But then he added, "I would argue that this goes a long way toward justifying our universe from nothing because it suggests inflation happened." Then he added " Moreover, total energy of any universe may be zero in a global sense. It is only well defined for a closed universe, for which it is definitely zero." (He told me he'd address all in detail in his new book.) OK, so here are my questions: If inflation gives us a possible method for creating a universe out of nothing, then how come it happened AFTER the big bang. Was the big bang created out of nothing too? And if the total energy "is only defined for a closed universe", how can we talk about it for a flat or open universe. THis all seems a bit muddled to me. Any thoughts on this would be greatly appreciated.

I donno. I think there is more to this man's visions than that. I'd like to hear what an expert psychologist or psychiatrist would say. My guess is that he is not alone. Maybe there is a medical name for this condition. I have had lucid dreams in the early morning just before I wake up. I am somehow aware that I am only dreaming. What is so cool is that the images seem so real. Sometimes I can will the dream - that is make things change inside the dream. It's fun. But having these oh so real images every time I close my eyes - I don't think I would like that.

First point. Yes, the deSitter binary star experminet showed that the speed of light is constant. Second point. I think the measurements taken on Earth in June and January were of light from a distant star. Say in June the Earth was moving in its orbit around the Sun towards the star. So then in January it was moving away from the star. The idea is to measure the speed of the light from the star at both times. And it measures as the same speed in June and in January. This means that the motion of the Earth (sone 60,000 miles an hour wrt to Sun) has no effect on the speed of the light from the star. In other words, the speed of light is unaffected by the speed of the observer (on Earth). Or as you put it, the speed of light is constant. Oh, and the Earth is NOT in the same inertial reference frame on January and June. The two reference frames are going in opposite directions. An "inertial" reference frame is one which is going in uniform motion, that is at a constant speed and in a constant direction. Each unique inertial reference frame has a unique constant speed and/or a unique constant direction.

I don't think that's right. I believe it goes something like this. Nothing can go faster than the speed of light through space, per special relativity. But the expansion of the universe is the expansion of space itself. And space can and does expand faster than the speed of light (per general relativity).

Thanks. I fixed the blog title and put in a new subtitle. It shows up with the new stuff on my blog, but not on the blog listing. I suppose this will take time?

I just posted my new blog; "It's Relative". But like a dope I put a slash into the title. How do I edit this out? And how do I change the subtitle "Just another science forum blog" to what I want? Please let me know.

I wish it were so. Scientists use the word "theory" for something that has a staggering amount of supporting evidence (like quantum theory, general relativity theory, and the theory of evolution). But they also us the same word "theory" for models that have virtually no supporting evidence (like string theory), and everything in between. So unfortunately, the lay public often gets confused. The only thing one can do is read up on these theories with a healthy skepticism, and try to find out how much empirical evidence there is for a given "theory".

I am wondering about virtual particles. As I understand it, in the Feynman view of QM, a particle and its anti-particle appear out of the "vacuum", collide, and annihilate each other. This all happens fast enough for given particle mass/energies so that the Uncertainty Principle on energy versus time is obeyed. But one virtual particle has positive energy and the other has negative energy. That's why there is no resultant energy produced (as oppossed to real particle-antiparticle collisions). So can we think of the particle with negative energy as having a negative mass per E=mc**2?