# Tag Info

2

Nope, not if you use the standard definition for "perpetual motion machines of the first kind", which can indefinitely produce work. Entropy increases monotonically over the entire universe, and eventually all free energy will be gone. This is known as heat death. Will particles in the universe continue moving forever? Probably. But that's not what ...

3

One has to define the terms one is using. Static point means a stationary point, an unchanging point In physics, motion is relative. One can define the earth as stationary, then everything else is moving around the earth in complicated mathematical functions. The simplest planetary model is to take the center of mass of the sun and the planets, then ...

1

In Special Theory of Relativity, all inertial reference frames are able to communicate with each other to share their results. And, they all agree with the value of c and related conclusions. In General Theory of Relativity, it's not always true. There are situations when two inertial reference frames may not be able to communicate with each other. In such ...

0

Since the super dense object that created the "big bang" created space and time, technically speaking, the "big bang" happened everywhere, as the amount of space the object took up expanded to be space as we know it now.

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In SR, there are global inertial reference frames and, in this context, no object moving with speed less than c in one reference frame moves with speed equal to or greater than c in any reference frame. But, in GR, in a curved spacetime, there are no global inertial reference frames. Instead, there are local inertial reference frames. We say ...

-4

The truth is, light speed isn't necessarily the fastest thing there is. If you went into your backyard and pointed a laser at one edge of the moon, and then moved it quickly to the other edge of the moon, your laser point on the moon would by moving on the moons surface faster than the speed of light. However, nothing that is not completely composed of ...

0

To expand on John Rennie's mention of several different (possible) types of multiverse, another one is Hugh Everett's "Many Worlds" interpretation of quantum mechanics. The idea is based on the maths behind a "wave function" - if you take the famous Double Slit experiment and look at the maths you have a wave function which describes a particle - now we can ...

3

A better way to think of it would be that space is being added to the universe; the universe is not "moving". Consider the case of two stars. The expansion of the universe doesn't cause the stars to "move" away from each other. Rather, space is created between the stars, resulting in them being further apart. This consequently, doesn't violate general ...

-5

The universe is not expanding faster than the speed of light. Red shift data from the most distant galaxies do not support this premise. Fact is, E=mc^2 is still the most used relation in physics, and it's Einstein's. This relation was derived assuming (as a postulate) that the speed of light to be both maximal and independent of the inertial reference ...

0

Electric charge is discrete, however mass and energy aren't. They're entirely described through quantum mechanics. In fact, most phenomena at the quantum level can be described as a wave function which specifies its location as a continuous probability. So if you were to describe the universe in one word, it would be quantum not discrete.

1

Finally the bottom line of question is, can we experimentally prove that energy, total energy is actually conserved ? (a Yes answer requires a detailed experiment with complete conservation and no loopholes) Elementary particle physicists have been doing this for more than sixty years. Conservation of energy is one of the main constraints that built ...

0

Physics generates theories that predict the behavior of the universe, and confirms or contradicts those theories with experiment. Physics ends where these activities do not work. There is no mainstream theory of God in physics. Nobody has been able to do any reproducible experiment that demonstrates the existence or non-existence of God, or that relates ...

0

In modern theoretical physics you can actually look back to a point in which they call "inflation" which is just 6.36 x 10^-34 of a second, i.e. the Planck Time, after the bang. The moment just when "our time" starts up, or comes into being if that makes sense. We are pretty sure about 300,000 after the big bang the universe was so hot the leftover heat is ...

0

There is not a universal rest frame. There is, however, a galactic rest frame. Because you can look up at the stars, falsely assume that they do not change, and count your rotations that way. However, that method is only as reliable as the premise that the stars don't move, which they do slightly. The Hafele-Keating experiment used a variant of this, ...

1

We model spacetime as a manifold and a metric. Broadly, the manifold gives us the dimensionality and connectivity while the metric provides a method of specifying distances. The equations of General Relativity allow us to calculate the metric from the stress-energy tensor (or vice versa if you're Miguel Alcubierre). The point that jinawee is making in his ...

0

I don't think we know for sure. For example see this article (the paper is on the Arxiv here) suggesting that the acceleration could be anisotropic. However if there is an anisotropy then it's small, and to a first approximation yes the acceleration is isotropic.

1

The (nearby) "separation between objects" you are referring to is the space-time metric. A metric in cosmology describes the expansion of space on large angular scales (low $\ell$ on the angular power spectrum of the universe). Without going into the mathematics, the expansion of space is driven by cosmic inflation, and is affected by things the amount and ...

1

There is a three dimensional shell of galaxies (none currently observed) that have a gravitational redshift relative to us that is consistent with a relative motion at the speed of light. If you moved to any other galaxy in the universe, there is a very high probability that they would observe a different such bubble. If you look sufficiently far into ...

2

This going to be a rather approximate answer because it involves lots of estimated quantities like the current density of matter and the value of the cosmological constant. The second Friedmann equation tells us: $$\frac{\ddot{a}}{a} = \frac{-4\pi G}{3}\left( \rho + \frac{3p}{c^2} \right) + \frac{\Lambda c^2}{3}$$ It's conventional to take $a = 1$ at ...

1

The actual question in this question, is a good physics question. Freely interpreted, it basically asks if SR effects, in particular time-ordering of spacelike separated events, make it difficult or impossible to simulate physics. The answer to that is no. An "external" Simulator (be it a particle physicist or the hypothetical people simulating our ...

0

Yes, you know - the many worlds theory is one of interpretations of quantum mechanics - so you can use quantum physics equation there (Like a probability by Born rule - the probability here can have a little different meaning). But the possible experiments what we would scientifically describe are (yet?) only speculations (Maybe because Copenhagen ...

1

We do have such structure in place: First, anything beyond the cosmological event horizon is effectively part of a different universe. An extension of that idea is the inflationary multiverse with bubble universes that can even have varying physical laws due to differently broken symmetries. String theory in turn adds its own flavour to that idea via the ...

2

If you are sincerely asking about the fate of spaceship departing the solar system, then you are asking a question about the standard model of cosmology. Instead of worrying about relativistic effects we'll concern ourselves with a photon that leaves our galaxy in a direction so that it hits nothing, and just keeps traveling. Faster than any spacecraft that ...

3

Fundamentally, the misconception here is that something that is expanding must be finite. This is simply not true. When we say the universe is expanding, we mean the distance between two stationary observers, sitting still as best they can, grows over time. But it is entirely possible for an infinite thing to have this property. Imagine the real number ...

-6

To start with, space was not created, space had always been there (yes even before the big bang). What was yet to be created was the incredible and ever expanding universe(Big bang ?). Space is infinite on it`s vastness and time because literally, space is the absence of stuff (sorry, couldnt think of a better word). Back to the answer: As you have heard ...

1

Time is relative. When it comes to Time Dilation, you actually see dilated time of another observer. So, your own time flow won't get frozen in any case. Hypothetically, you can see another one's time frozen if she is traveling at speed of light (time dilation by speed) or she is at event horizon of Black Holes (gravitational time dilation). Unfortunately, ...

2

It's important to distinguish between time and the flow of time. In any universe we need four numbers to uniquely identify a spacetime point, and we conventionally choose one of the coordinates to be time and the other three space so the location of a spacetime point is given by $(t, x, y, z)$. Assuming the universe doesn't hit a singularity then for every ...

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The Wikipedia diagram is giving the breakdown by mass not by volume. Baryonic/leptonic (i.e. non-dark) matter is only about 5% of all matter and of that four fifths of it is in the form of free hydrogen and helium. Of the remaining 1% about half is neutrinos or heavy elements. That means only 0.5% of the mass/energy in the universe is in stars.

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The answer to (2) is simply that no-one knows, and further that it's unlikely we will ever know. It's impossible to prove that the universe is infinite, but it's just possible we might prove it closed and therefore finite if the length scale is around the size of the currently observable universe. The paper Topology of the Universe: Theory and Observations ...

1

According to the Deep Astronomy webpage on the HUDF 3D, These galaxies, while standing absolutely still, are racing away from us, in some cases faster than the speed of light. The spacetime between us and everything else grows larger by the minute, pushing the galaxies in this image to a distance of over 47 billion light years. So if the image is 47 ...

0

The light from the universe outside the event horizon of the black hole should be visible as a small disc or point light source in the direction facing away from the singularity. This will happen even before you reached the event horizon. You do not need to cross the horizon to see this effect. At ergosphere distance the BH will cover half of the sky ...

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