# Traveling at Near-Light Speed: Time Dilation and Your Perspective Explained

• csnsc14320
In summary, if you were to travel just short of the speed of light, it would take you about a year to reach an object one light year away from the perspective of someone on Earth. However, from your own perspective, it could be a very short period of time due to time dilation. This raises the question of just how far away the object truly is, as from your perspective it could be much closer. Additionally, if you were to travel at a constant acceleration of 1 gee, you could theoretically travel huge distances in a short amount of time from your perspective, but your home would age significantly during the journey. This phenomenon becomes even more extreme as you approach the speed of light, with a near-instantaneous journey from your

#### csnsc14320

I'm just wondering:

Say you obtain a spaceship that can travel just short of the speed of light.

If you travel to ao object "one light year" away, would it take you one year to get there from YOUR perspective, or from some stationary person on Earth's perspective?

Because I know that the closer you get to the speed of light, the slower time passes for you relative to people at rest

So, basically, I'm wondering if, from your perspective, it takes one year to get there or some shorter time

If you travel just short of the speed of light - from the perspective of someone on Earth - then to them it takes you about a year to get there. From your perspective, it could be a very short period of time.

russ_watters said:
If you travel just short of the speed of light - from the perspective of someone on Earth - then to them it takes you about a year to get there. From your perspective, it could be a very short period of time.

really? because i have always wondered that, if it is 50 million light years to the center of our galaxy, then there is really no hope of ever getting too far since that's an excruciatingly long amount of time

so if you were to travel just short of light speed, you could theoretically travel huge distances in what seems like a short amount of time for you? (although your home would be 50 million years older)

csnsc14320 said:
really? because i have always wondered that, if it is 50 million light years to the center of our galaxy, then there is really no hope of ever getting too far since that's an excruciatingly long amount of time

so if you were to travel just short of light speed, you could theoretically travel huge distances in what seems like a short amount of time for you? (although your home would be 50 million years older)
Yep, that's right

diazona said:
Yep, that's right

crazy stuff :p

thanks

Even crazier things happen if you don't return. Say your friends back home are sending you messages. How many years would you see go by in their messages?

Depends on your means of getting close to lightspeed, but say you're accelerating at 1 gee. Then once you've traveled more than a few light-years, the time-difference between when you left and the messages from home you receive on coming to a halt at the Galactic Core, or wherever, is just 1.9 years. That's the difference between light's travel time and yours, regardless of how far you go, if you accelerate constantly the whole way.

think about russ' response above for a moment - from the perspective of someone on Earth watching you, it would take you just over a year to get there - BUT from your own perspective, you will have traveled that "one light year" in far less that a year - which brings up the question of "just how far away is that star?" from your perspective, you have either traveled faster than the speed of light, or the star is not "really" 1 LY away.

from Earth's perspective, again, it is 1 LY, but from your ship's perspective, it is perhaps only a few million miles (depending on how close to C you are traveling). if you could actually travel at C, people on Earth would say it took you exactly one year to arrive, but from your perspective, you would be there instantaneously, since time does not exist at C. so, how far away is that star, really?

csnsc14320 said:
really? because i have always wondered that, if it is 50 million light years to the center of our galaxy, then there is really no hope of ever getting too far since that's an excruciatingly long amount of time

so if you were to travel just short of light speed, you could theoretically travel huge distances in what seems like a short amount of time for you? (although your home would be 50 million years older)
FYI, it is "only" about 50,000 light-years to the center of our galaxy, not 50 million. But even that is an excruciatingly long distance / travel time.

PhysicsDilettante said:
FYI, it is "only" about 50,000 light-years to the center of our galaxy, not 50 million. But even that is an excruciatingly long distance / travel time.

50,000 ly to the Core and back. The current best estimate puts the Core about ~26,000 ly away. But if one was flying to the very heart of the Virgo Super-Cluster then it'd be about 50 million ly. Would be quite a challenging trip.

Ursula LeGuin's Nearly-as-Fast-as-Light (NAFAL) starships, from her Hainish stories, can do 256 ly in 10.65 hours of subjective time. If acceleration was (near) instantaneous then the time-distortion factor (TDF) would be ~210,000. Constant acceleration would need to be at 25,000 g and a peak TDF of ~2,700,000. For constant acceleration the ratio of cosmic time to subjective time is ln(2*TDF)/(TDF) for high TDF (above about 10.)

BTW what I'm calling TDF is normally referred to as γ <gamma>, and is equal to ~1/√[1 - (v/c)²] so the speed is incredibly close to lightspeed, a gnat's whisker per century difference in speed for that trip to Virgo...

they say that if you could continually accelerate at one g (from your perspective I guess) then you could go virtually anywhere in the universe in one lifetime. I've always found that to be a very surprising result. I think you have to use 'rapidity' to calculate it.

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granpa said:
they say that if you could continually accelerate at one g (from your perspective I guess) then you could go virtually anywhere in the universe in one lifetime. I've always found that to be a very surprising result. I think you have to use 'rapidity' to calculate it.

See

around 2.4 months from your perspective. 1 year to the rest of us.

## 1. How does traveling at near-light speed affect time?

Traveling at near-light speed causes time dilation, meaning that time appears to pass more slowly for the person traveling at that speed compared to someone who is stationary. This effect becomes more pronounced as the speed increases, with time appearing to slow down significantly as the speed approaches the speed of light.

## 2. Why does time dilation occur at near-light speed?

Time dilation is a result of Einstein's theory of relativity. According to this theory, time and space are interconnected, and the speed of light is the universal speed limit. As an object approaches the speed of light, it experiences a slowing of time to maintain the constant speed of light in relation to its surroundings.

## 3. How does time dilation affect a traveler's perspective?

From the perspective of the traveler, time will appear to pass normally. However, when they return to their starting point after traveling at near-light speed, they will find that less time has passed for them compared to the people who stayed behind. This is known as the twin paradox, where one twin who travels at near-light speed will age slower than the other twin who remains stationary.

## 4. Is it possible to travel at exactly the speed of light?

No, it is not possible for an object with mass to travel at the speed of light. As an object approaches the speed of light, its mass increases infinitely, making it impossible to reach that speed.

## 5. Can time travel occur when traveling at near-light speed?

While time dilation may make it seem like time travel is occurring, it is not possible to travel back in time by traveling at near-light speed. The traveler will always move forward in time, just at a slower rate compared to those who are stationary. Additionally, the immense energy required to travel at near-light speed makes it currently impossible to achieve in reality.