# Moving At Light Speed

#### 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

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

#### DaveC426913

Gold Member
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

#### DaveC426913

Gold Member
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

Gold Member
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

v2kkim said:
cragar said:
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

Gold Member
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

##### timelike observer
Homework Helper
Gold Member
Ich said:
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

Gold Member
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

Gold Member
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

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?

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