Moving at Light Speed: Relativistic Effects Explained

[T.O.E Dream]

if we were able to move at the speed of light (somehow) how would things change due to the relativistic effects.
Take this for example: if we were to go somewhere moving at 100 percent of c,and for simplicity say that it's 100 light years away, what would we feel or think?
i know if we were moving at anywhere lower than c for example half of the speed of light our perspective of the spacetime don't change, meaning that we don't see ourselves smaller and that time doesn't seem to go by slower but someone stationary observing us will see our actions happen in hyperslow motion. And since time doesn't goes by at the speed of light meaning that a photon won't age a bit since the big bang what will happen to us.
Will we be frozen in the same frame? will we reach our destination in an instance from our perspective?

 

[cristo]

We wouldn't be able to move at the speed of light, since only massless bodies can travel at the speed of light.

 

[DaveC426913]

The question you want to ask is: how would things change if we were able to move at ALMOST the speed of light.

 

[cragar]

I have a physics book and it talks about if we had a rocket and we could
travel at 95% the speed of light you could go anywhere in the cosmos in ones lifetime
because time would slow down so much for u . you could travel to canopus a star that is 99 light years away in 5 minutes relative to u .

 

[T.O.E Dream]

Okay I know we can't move at the speed of light so instead pretend, just pretend we were a photon and if we were moving at 100 percent c, would we every be able to actually do anything since no time passes meaning it'll slow down so much that our actions will stay in the same frame forever and if no time passes does that mean we'll reach a certain place instantly from our own perpective

 

[Dale]

http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/headlights.html

http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html

http://math.ucr.edu/home/baez/physics/Relativity/SR/Spaceship/spaceship.html

 

[DaveC426913]

Okay I know we can't move at the speed of light so instead pretend, just pretend we were a photon and if we were moving at 100 percent c, would we every be able to actually do anything since no time passes meaning it'll slow down so much that our actions will stay in the same frame forever and if no time passes does that mean we'll reach a certain place instantly from our own perpective

Photons do not experience time and so have no perspective.

A photon does not "travel" from point to point in three dimensions, it is simply a straight, static line connecting two points in 4 dimensional space-time (which is static and unchanging). There is no perspective.

 

[cragar]

when a photon travels through glass does it expierence time

 

[v2kkim]

when a photon travels through glass does it expierence time

Really ? What is the possible implication of it to other related physical phenomina ? How can we detect it ?

 

[cragar]

I don’t know , you probably think I am retarded.

 

[DaveC426913]

when a photon travels through glass does it expierence time

Was this a question? It could be interpreted as a question or a statement.

If a question, the answer is: no, it does not experience time.

The piece of glass is an object in space-time. The photon is a line connecting point a to point b that intercepts the glass, where the photon's line is kinked. There is no "passage" of time.

 

[cragar]

ok i see yes it was a ?

 

[Ich]

when a photon travels through glass does it expierence time

Really ? What is the possible implication of it to other related physical phenomina ? How can we detect it ?

Strongly coupled photons in solids are no longer called photons, but polaritons. The finite lifetime of polaritons proves that they experience time.

 

[DaveC426913]

The finite lifetime of polaritons proves that they experience time.

Photons also have a finite lifetime. Finite lifetimes prove nothing about experiencing time. It merely proves they have a finite length in space-time.

 

[T.O.E Dream]

when a photon travels through glass does it expierence time

I kind of understand why you asked that, probably because light travels at 100 percent of c in a vacuum. While if it moves through air or i guess glass, the speed of it slows down meaning it might experience some but very little time. But I'm not sure that's right. The photon might not slow down individually. Again, I'm not sure cause I'm not a huge expert.

 

[robphy]

The finite lifetime of polaritons proves that they experience time.

Photons also have a finite lifetime. Finite lifetimes prove nothing about experiencing time. It merely proves they have a finite length in space-time.

While the verb "experience" has be fully defined,
one can make the following statement:
Given a light ray from event-A to the future-event-F,
event-F is causally-after event-A [independent of observer].
That is, A happens then F happens.
It appears this can be generalized to a sequence of events A,B,...,E,F on the same light ray:
A happens, then B happens, ... then E happens, then F happens.

(While massive-particles are able to assign a "clock reading" to each event,
it's not obvious how to do this for massless particles.)

 

[Ich]

Photons also have a finite lifetime.

Photons do not decay, and that's what I mean with "finite lifetime". Massless particles cannot decay, because they experience no time. If a particle decays, it experiences time and cannot be massless.

 

[DaveC426913]

Photons do not decay, and that's what I mean with "finite lifetime". Massless particles cannot decay, because they experience no time. If a particle decays, it experiences time and cannot be massless.

I'm not talking about decay, I'm talking about emission and absorption. A photon emitted from the coil of a flashlight and absorbed by the atoms in the wall has a finite lifetime, yet it experiences no time; it simply manifests as a static line in space-time connecting flashlight and wall.

 

[DaveC426913]

I kind of understand why you asked that, probably because light travels at 100 percent of c in a vacuum. While if it moves through air or i guess glass, the speed of it slows down meaning it might experience some but very little time. But I'm not sure that's right. The photon might not slow down individually. Again, I'm not sure cause I'm not a huge expert.

No. A photon's passage thorugh a medium does not affect its ... uh ... non-experience of time. A photon always travels at c, though its progress through a medium may not get it from point A to point B at the speed of c.

 

[Ich]

I'm not talking about decay,

So why are you responding at all to my posts? Your talking about absorption is completely off topic. I'm talking about polariton decay and what insight one might gain from it, in response to v2kkim's question.
Maybe you want to contribute to the discussion?

 

[DaveC426913]

So why are you responding at all to my posts? Your talking about absorption is completely off topic. I'm talking about polariton decay and what insight one might gain from it, in response to v2kkim's question.
Maybe you want to contribute to the discussion?

Go wild. Demonstrate how this will contribute to his understanding of a "photon's perspective", which is what his question is about.

 

[Ich]

Demonstrate how this will contribute to his understanding of a "photon's perspective", which is what his question is about.

It seems you forgot what v2kkim asked:

What is the possible implication of it to other related physical phenomina ? How can we detect it ?

If a photon couples to the lattice, it effectively gains mass and goes slower than c. The dispersion relation gets quite different from that of a free photon. It travels no longer along a null geodesic, thus it experiences proper time. Because proper time ticks, it can decay spontaneously, which is impossible for a free photon.

Go wild.

Calm down.

 

[madmike159]

when a photon travels through glass does it expierence time

There have been lots of topics on this. The speed of light in glass is lower than c but photons still move at c.

 

[JarodB]

The fact of the matter is you CAN move at the speed of light, and you CAN move even faster, much faster.

Lets go pre-bigbang. According to Planck all matter has a wave like nature, so let's try and find lambda of the 'visable' universe.

6.626 x 10^-34 / 3x10^52 x 299,458,792 = 7.36739566 x 10^-95 (lambda)

Well well well, look at that! Thats infetesibly small, much smaller then a "Planck" length.
Assuming that the smallest unit is 10^-35, this simply can't be true.

So, 6.626 x 10^-34 / 3x10^52 x (x)

(x) ~ .73176 x 10^51

So, we can conclude the universe expanded greater then .73176 x 10^51 with all of its mass.

Or, you can go as small as you want. It's either one or the other.

 

[cragar]

i thought it was Louis de Broglie who first said that all matter has an associated wave.
and how do u go pre-bang if u believe in the big-bang that was the start.

 

[madmike159]

what is 3x10^52 ment to be?

 

[JarodB]

what is 3x10^52 ment to be?

the mass of the visable universe

 

[JarodB]

i thought it was Louis de Broglie who first said that all matter has an associated wave.
and how do u go pre-bang if u believe in the big-bang that was the start.

The big bang was the "explosion" from a very very small ball of infinitly dense matter, before the explosion was just the ball of matter / energy.

 

[cragar]

what was before the ball of matter and energy and we would have to go back to when time didn't exist.

 

[DaveC426913]

The big bang was the "explosion" from a very very small ball of infinitly dense matter, before the explosion was just the ball of matter / energy.

The Big Bang was not an explosion.


Also, there was no matter until loooooong after, when the universe had cooled enough to allow matter to condense out of energy.

 

[neopolitan]

The big bang was the "explosion" from a very very small ball of infinitly dense matter, before the explosion was just the ball of matter / energy.

I think you might have the right sort of idea, but there are some serious misstatements.

A very very small ball of infinitely dense matter is indistinguishable from a very big ball of infinitely dense matter. It has infinite mass. If the age of the universe is not infinite, then the volume of the universe is not infinite and if you put an infinite mass in a finite universe the matter is still going to be infinitely dense.

As Dave said, it wasn't matter originally anyway. Nor was the big bang an explosion. Perhaps it is worth remembering that "big bang" was initially a pejorative. It wasn't meant to describe what is now the standard cosmological model, it was meant to ridicule it.

Plus, you say "before the explosion was just the ball of matter / energy" which implies (even if not intentionally) that the "ball" was surrrounded by empty space on top of suggesting that there was a sensible "before". At t=0 (where t is now about 14 billion years), there was nothing. At t=t_pl, a Planck time, there was the entire energy of the universe as tightly compacted as it can be.

Here's where I have to bow to quantum physicists, I suspect that the maximum amount of energy you can fit into one Planck cube (or a Planck volume) is the energy associated with the Planck mass (it is also the energy associated with a photon with a frequency of 1/t_pl). (The wikipedia article on http://en.wikipedia.org/wiki/Planck_energy" says this is "probable".)

So, if I am right, one Planck time after t=0, all the energy of the universe would be in a quite small space (with a radius of about 10^-15). After the second Planck time, it would be a radius of about 10cm (very roughly). This would require the space to have expanded at greater than the speed of light with a very high Hubble constant, but that would be consistent with a Hubble constant which corresponds with the age of the universe (as it does today) and the fact that the edges of the universe would be outside of the Hubble distance for that value of the Hubble constant. (The Hubble distance is the distance away that something has to be to be moving at the speed of light. That makes it the radius of the observable universe.) I also think that other factors would come into play, like gravity (because concentrations of energy resist the expansion of the universe, as do galaxies today) and heat, although this may not figure until you get condensation of matter.

After that, I think you would have something akin to an explosion (to the same extent that quickly blowing up a balloon without it bursting is an explosion), or at least the beginnings of lumpiness in the universe.

Anyway, at Planck time, the energy of the universe was not associated with one photon with a very high frequency (just not possible), nor was it infinitely dense. If the Hubble constant is linked to the age of the universe, then it doesn't make sense to have any before the big bang. (Although, to be as comprehensive as I can, it is not impossible that the Hubble constant represents the age of the universe since the big bang. That just means that the time before the big bang is meaningless, in a similar way that time in an empty static universe would be meaningless.)

cheers,

neopolitan

 

[cragar]

When did time start

 

[madmike159]

At the big bang.So the big bang was t = 0

 

[Dmitry67]

So, if I am right, one Planck time after t=0, all the energy of the universe would be in a quite small space (with a radius of about 10^-15). After the second Planck time, it would be a radius of about 10cm (very roughly).

It always puzzled me, how 10^34 plank distances can be created during 1 plank time...

 

[madmike159]

It always puzzled me, how 10^34 plank distances can be created during 1 plank time...

Well planks length is the distance light can travle in planks time ($$t_{p}\ =\ 5.3906(40)\ \times\ 10^{-44}\ s$$), we know the universe is slowing down exponentially but we don't know if it will stop and collaps on its self.