MDMs should last a little longer than they do

Yup. Classic.

TFLYTSNBN wrote:

Daryl wrote:I still remember a decades old quote from an Analog Magazine.
If it takes infinite energy to accelerate up to exactly C, and at that point the space ship relative to the stationary reference is infinitely heavy, all would be attracted to it, possibly forming a pin point big bang source.
Thus while it may be true that a space ship could attain C, it would only be one per universe.

Paul Andrson.
TAU ZERO

I don't know if my thinking is correct here, but wouldn't the run times for the MDM's be correct if we consider the missiles being affected by an external gravity field?

My understanding of the wedges implies that a ship or missile is essentially "falling" towards a point in space determined by the geometry of the wedge.

Joat42 wrote:I don't know if my thinking is correct here, but wouldn't the run times for the MDM's be correct if we consider the missiles being affected by an external gravity field?

My understanding of the wedges implies that a ship or missile is essentially "falling" towards a point in space determined by the geometry of the wedge.

You're right that a gravity well deforms space-time and causes time dilation. THAT math is beyond me.

But I can tell the direction of the math: the deeper you are in the gravity well, the slower time goes for you. So if an MDM's engines last 9 minutes in flat space time, the gravity source warping space-time will make the observer at rest measure T > 9 min.

ThinksMarkedly wrote:

Joat42 wrote:I don't know if my thinking is correct here, but wouldn't the run times for the MDM's be correct if we consider the missiles being affected by an external gravity field?

My understanding of the wedges implies that a ship or missile is essentially "falling" towards a point in space determined by the geometry of the wedge.

You're right that a gravity well deforms space-time and causes time dilation. THAT math is beyond me.

But I can tell the direction of the math: the deeper you are in the gravity well, the slower time goes for you. So if an MDM's engines last 9 minutes in flat space time, the gravity source warping space-time will make the observer at rest measure T > 9 min.

My thinking was that the run time is given for flat space observation, regardless of the run time for the missile's local frame reference.

I guess unless rfc chimes in on the subject it'll be hard to nail down exactly what's going on.

Joat42 wrote:My thinking was that the run time is given for flat space observation, regardless of the run time for the missile's local frame reference.

I guess unless rfc chimes in on the subject it'll be hard to nail down exactly what's going on.

Someone suggested the same thing, that the time is tied to the observer at rest compared to the local star. Or at rest compared to the alpha barrier, which is probably the same. This may be it.

Just note that the acceleration as measured by the missile is much higher. I calculated that a ship @ 700G after 6h would measure 1066G of acceleration. Well, a missile at 46000G after 8 minutes and 51 seconds (when it's at 0.799c) would measure much more than that: 4.6x more, roughly 211600 gravities.

Which may not be a problem. Just a footnote to make Einstein weep.

ThinksMarkedly wrote:

Joat42 wrote:My thinking was that the run time is given for flat space observation, regardless of the run time for the missile's local frame reference.

I guess unless rfc chimes in on the subject it'll be hard to nail down exactly what's going on.

Someone suggested the same thing, that the time is tied to the observer at rest compared to the local star. Or at rest compared to the alpha barrier, which is probably the same. This may be it.

Just note that the acceleration as measured by the missile is much higher. I calculated that a ship @ 700G after 6h would measure 1066G of acceleration. Well, a missile at 46000G after 8 minutes and 51 seconds (when it's at 0.799c) would measure much more than that: 4.6x more, roughly 211600 gravities.

Which may not be a problem. Just a footnote to make Einstein weep.

Well, the physics of Honorverse seems to be a bit modified compared our verse anyway so Einstien in Honorverse may have been jumping with joy.

Yea well don't forget DW also has constant acceleration which means the power required grows exponentially for every second under power...

Jonathan_S wrote:For whatever reason (probably in no small part because it makes the math simpler) no ship or missile under impeller drive has ever paid attention to relativistic effects on acceleration.


My personal handwave is that somehow - magically - the energy siphon effect that helps power the wedges by stealing power from hyperspace manages to scale up its power and the node's output perfectly matched to retarding effect of increased relativistic mass. So the two "just happen" to cancel out and give you the same numbers that Newtonian physics would have if it applied to those operating regimes.

Another possibility that doesn't require nearly the handwave is to figure that since the propulsion source is the interaction with space itself and space isn't moving that the effects are measured in the reference frame of the space rather than the reference frame of the ship or missile.

We do know that so long as it's inside the wedge the mass involved is basically irrelevant. Thus power isn't the limiting factor--the effects are otherwise limited. (We have also seen that starship drives are actually capable of far more acceleration than is ever used. There would be no reason to overpower them like this unless there was some situation where that power could be used--and if they are operating in a frame of reference other than that of the ship it makes sense.

Relax wrote:Yea well don't forget DW also has constant acceleration which means the power required grows exponentially for every second under power...

This growth (which isn't exponential, it's hyperbolic), is only if you measure from the frame of the ship that launched the missile. From the missile's point of view, nothing happened: at any point in time, its mass is unchanged from the moment before and it's current, relative velocity is 0 (the rest of the Universe is accelerating past it). If the mass is the same and the acceleration is constant, the force required to accelerate is constant too. Since the force is constant, the energy is constant too.

We can approximate that the mass is roughly the same because the missile doesn't expel mass as reaction mass. Hydrogen fusion converts mass to energy at a worse than 1% efficiency ratio, so less than 1% of the fuel mass will radiate as energy.

From the frame of reference of someone who did not accelerate, like the ship that fired the missile, knowing that its power plant and drive efficiency don't change, but measuring relativistic effects, that observer will conclude the mass increased. And because this observer calculates that the mass increased, they will calculate that the energy required to continue accelerating also increase. But if the observer accelerates in the same direction that the missile is moving, she'll measure the mass decreasing again.

Now, for all intents and purposes of that observer, the mas has increased, due to energy-mass equivalence and the energy-momentum relation under relativistic speeds. When we hear about particle physicists talk about 1 GeV particles, they mean at the same time the particle's (kinetic) energy, the particle's speed and the particle's relativistic mass. This is all given by the equations E² = m²c⁴ = m₀²c⁴ + p²c² (p is momentum; in natural units where c = 1 and if m₀ is so small that it can be ignored, E² = m² = p² → E = m = p).

Loren Pechtel wrote:Another possibility that doesn't require nearly the handwave is to figure that since the propulsion source is the interaction with space itself and space isn't moving that the effects are measured in the reference frame of the space rather than the reference frame of the ship or missile.

We do know that so long as it's inside the wedge the mass involved is basically irrelevant. Thus power isn't the limiting factor--the effects are otherwise limited. (We have also seen that starship drives are actually capable of far more acceleration than is ever used. There would be no reason to overpower them like this unless there was some situation where that power could be used--and if they are operating in a frame of reference other than that of the ship it makes sense.

You're probably right and I concluded something similar too. But instead of talking about the frame of reference of space, I talked about the frame of reference of the local star or other massive body. After all, stars aren't at rest, they are moving around the centre of the galaxy and bobbing up and down the plane of the galactic disk. In hyperspace, it would be measured against something else.

See also https://en.wikipedia.org/wiki/Frame-dragging to see that massive objects and energy concentration can cause space to move too. Space moving is, after all, the principle of the Alcubierre Warp Drive.

The distinction is rather pedantic, I know. It's unlikely to make a difference in practice, since the speediest objects we know of (https://en.wikipedia.org/wiki/Hypervelocity_stars) are moving relative to everyone else in the galaxy in the order of 1000 km/s, which is 0.0033c.

This proposition (yours and mine) has one very measurable effect: the acceleration measured by an observer riding the missile or inside the ship. Because we know that time dilation does occur, if we say the acceleration is measured by an observer at rest relative to space or the star, then those suffering from time dilation will measure bigger accelerations. See one of my earlier posts in this thread where I calculated the acceleration measured by someone inside a ship at nominal 700G for 6 hours and for the missile at a nominal 46000G for 9 minutes.